TranscriptionGet This Book!Page by:OpenStax CollegeSummaryIn both prokaryotes and eukaryotes, the second function of DNA (the first was replication) is to provide the information needed to construct the proteins necessary so that the cell can perform all of its functions. To do this, the DNA is read or transcribed into anmRNAmolecule. The mRNA then provides the code to form a protein by a process called translation. Through the processes of transcription and translation, a protein is built with a specific sequence of amino acids that was originally encoded in the DNA. This module discusses the details of transcription.The Central Dogma: DNA Encodes RNA; RNA Encodes ProteinThe flow of genetic information in cells from DNA to mRNA to protein is described by the central dogma (Figure), which states that genes specify the sequences of mRNAs, which in turn specify the sequences of proteins.The central dogma states that DNA encodes RNA, which in turn encodes protein.The copying of DNA to mRNA is relatively straightforward, with one nucleotide being added to the mRNA strand for every complementary nucleotide read in the DNA strand. The translation to protein is more complex because groups of three mRNA nucleotides correspond to one amino acid of the protein sequence. However, as we shall see in the next module, the translation to protein is still systematic, such that nucleotides 1 to 3 correspond to amino acid 1, nucleotides 4 to 6 correspond to amino acid 2, and so on.Transcription: from DNA to mRNABoth prokaryotes and eukaryotes perform fundamentally the same process of transcription, with the important difference of the membrane-bound nucleus in eukaryotes. With the genes bound in the nucleus, transcription occurs in the nucleus of the cell and the mRNA transcript must be transported to the cytoplasm. The prokaryotes, which include bacteria and archaea, lack membrane-bound nuclei and other organelles, and transcription occurs in the cytoplasm of the cell. In both prokaryotes and eukaryotes, transcription occurs in three main stages: initiation, elongation, and termination.InitiationTranscription requires the DNA double helix to partially unwind in the region of mRNA synthesis. The region of unwinding is called atranscription bubble. The DNA sequence onto which the proteins and enzymes involved in transcription bind to initiate the process is called apromoter. In most cases, promoters exist upstream of the genes they regulate. The specific sequence of a promoter is very important because it determines whether the corresponding gene is transcribed all of the time, some of the time, or hardly at all (Figure).The initiation of transcription begins when DNA is unwound, forming a transcription bubble. Enzymes and other proteins involved in transcription bind at the promoter.ElongationTranscription always proceeds from one of the two DNA strands, which is called thetemplate strand. The mRNA product is complementary to the template strand and is almost identical to the other DNA strand, called thenontemplate strand, with the exception that RNA contains a uracil (U) in place of the thymine (T) found in DNA. During elongation, an enzyme calledRNA polymeraseproceeds along the DNA template adding nucleotides by base pairing with the DNA template in a manner similar to DNA replication, with the difference that an RNA strand is being synthesized that does not remain bound to the DNA template. As elongation proceeds, the DNA is continuously unwound ahead of the core enzyme and rewound behind it (Figure).During elongation, RNA polymerase tracks along the DNA template, synthesizes mRNA in the 5' to 3' direction, and unwinds then rewinds the DNA as it is read.TerminationOnce a gene is transcribed, the prokaryotic polymerase needs to be instructed to dissociate from the DNA template and liberate the newly made mRNA. Depending on the gene being transcribed, there are two kinds of termination signals, but both involve repeated nucleotide sequences in the DNA template that result in RNA polymerase stalling, leaving the DNA template, and freeing the mRNA transcript.On termination, the process of transcription is complete. In a prokaryotic cell, by the time termination occurs, the transcript would already have been used to partially synthesize numerous copies of the encoded protein because these processes can occur concurrently using multiple ribosomes (polyribosomes) (Figure). In contrast, the presence of a nucleus in eukaryotic cells precludes simultaneous transcription and translation.Multiple polymerases can transcribe a single bacterial gene while numerous ribosomes concurrently translate the mRNA transcripts into polypeptides. In this way, a specific protein can rapidly reach a high concentration in the bacterial cell.Eukaryotic RNA Processing

ImportanceBacteria are present in large numbers in raw wastewater, in biological treatment plants, in plant effluent, in natural waters, and throughout our environment. In the wastewater treatment plant, they form part of the slime on trickling filters and on the discs of rotating biological contactors. They are also present in activated sludge.Bacteria areheterotrophs, meaning that they get their food from eating other organisms or from eating organic matter. (In contrast, organisms like plants which make their own food are known asautotrophs.) As a result, bacteria are important to the wastewater operator since the bacteria are able to digest a large amount of the waste in wastewater. On the other hand, some bacteria get their food from living inside organisms such as humans, in which case they can cause disease.

4.5 Enzymeshttp://biologyforlife.wordpress.com/2011/09/09/4-5-enzymes/Biology for Life

How are enzymes synthesized?

JulieyumiAnswered LastEnzymes are proteins that are first transcribed from DNA into mRNA, then translated from mRNA to proteins.ecialized Cell Structure and FunctionProtein SynthesisSpecialized Cell Structure and Function Introduction Modifications and Adaptive Functions Cellular Respiration Protein SynthesisThe making of the various types of protein is one of the most important events for a cell because protein not only forms structural components of the cell, it also composes the enzymes that catalyze the production of the remaining organic biomolecules necessary for life. In general, the genotype coded for in the DNA is expressed as a phenotype by the protein and other enzyme-catalyzed products.The DNA housed in the nucleus is too large to move through the nuclear membrane, so it must be copied by the smaller, single-stranded RNA (transcription), which moves out of the nucleus to ribosomes located in the cytoplasm and rough endoplasmic reticulum to direct the assembly of protein (translation). The genes do not actually make the protein, but they provide the blueprint in the form of RNA, which directs the protein synthesis.TranscriptionTranscriptionoccurs in the cell nucleus and represents the transfer of the genetic code from DNA to a complementary RNA. The enzyme RNA polymerase Attaches to and unzips the DNA molecule to become two separate strands. Binds topromotersegments of DNA that indicate the beginning of the single strand of DNA to be copied. Moves along the DNA and matches the DNA nucleotides with a complementary RNA nucleotide to create a new RNA molecule that is patterned after the DNA.The copying of the DNA continues until the RNA polymerase reaches atermination signal, which is a specific set of nucleotides that mark the end of the gene to be copied and also signals the disconnecting of the DNA with the newly minted RNA.The three types of RNA are mRNA (messenger RNA) is transcribed from DNA and carries the genetic information from the DNA to be translated into amino acids. tRNA (transfer RNA) interprets the three-letter codons of the nucleic acids to the one-letter amino acid word rRNA (ribosomal RNA) is the most abundant type of RNA, and along with associated proteins compose the ribosomes.When the RNA polymerase is finished copying a particular segment of DNA, the DNA reconfigures into the original double-helix structure. The newly created mRNA moves out of the nucleus and into the cytoplasm.TranslationTranslationis the conversion of information contained in a sequence of mRNA nucleotides into a sequence of amino acids that bond together to create a protein. The mRNA moves to theribosomesand is read by tRNA, which analyzes sections of three adjoining nucleotide sequences, calledcodons, on the mRNA and brings the corresponding amino acid for assembly into the growing polypeptide chain. The three nucleotides in a codon are specific for a particular amino acid. Therefore, each codon signals for the inclusion of a specific amino acid, which combines in the correct sequence to create the specific protein that the DNA coded for.The assembly of the polypeptide begins when a ribosome attaches to astart codonlocated on the mRNA. Then tRNA carries the amino acid to the ribosomes, which are made of rRNA and protein and have three bonding sites to promote the synthesis. The first site orients the mRNA so the codons are accessible to the tRNA, which occupy the remaining two sites as they deposit their amino acids and then release from the mRNA to search for more amino acids. Translation continues until the ribosome recognizes a codon that signals the end of the amino acid sequence. The polypeptide, when completed, is in its primary structure. It is then released from the ribosome to begin contortions to configure into the final form to begin its function.BionoteEach codon on the mRNA specifies a particular amino acid, which is recognized by the anticodon of the complementary tRNA. There are 20 different amino acids; there are also 20 different tRNA molecules.

After the proteins are made, they are packaged and transported to their final destination in an interesting pathway that can be described in three steps involving three organelles:1. Vesiclestransport the proteins from the ribosomes to theGolgi apparatus, a.k.a Golgi complex, where they are packaged into new vesicles.2. The vesicles migrate to the membrane and release their protein to the outside of the cell.3. Lysosomesdigest and recycle the waste materials for reuse by the cell.Enzymes within the Golgi apparatus modify the proteins and enclose them in a new vesicle that buds from the surface of the Golgi apparatus. The Golgi apparatus is often seen as the packaging and distribution center of the cell.Vesicles are small, membrane-enclosed envelopes that are usually made in the endoplasmic reticulum or Golgi apparatus and are used to transport substances through the cell.Lysosomes are a special type of vesicle that contains the digestive enzymes for the cell and are useful in breaking down leftover waste products of proteins, lipids, carbohydrates, and nucleic acids into their component parts for reassembly and reuse by the cell.

Read more:Specialized Cell Structure and Function: Protein Synthesis | Infoplease.comhttp://www.infoplease.com/cig/biology/protein-synthesis.html#ixzz3CqTikKYpremember that enzymes are proteins so how they are made can be explained by the process of protein synthesis.

1.) The cell receives a signal that loosens the DNA and makes the wanted gene available for transcription.

2.) Transcription: The information provided by DNA is then transcribed into RNA. RNA processing takes place in the nucleus before it leaves for the cytoplasm. This RNA strand is the "messenger RNA" or mRNA for short.

3.) Translation: The mRNA then leaves the nucleus and goes through translation in the cytoplasm. Here, ribosomes meet the mRNA and translates the nucleotides into amino acids. A combination of three nucleotides (codon) = one amino acid. Remember that amino acids are the building blocks of proteins.

4.) The amino acids are then covalently bonded to one another. This produces a polypeptide, another name for protein.

5.) The polypeptide chain will then fold up to accordingly and may go to the rough ER for further modifications and/or the Golgi Body for transportation in/around/out the cell, depending on the protein's function.

After making changes to the protein in the Golgi Body, then the protein is ready to work! Enzymes vary in structure and therefore vary in their function. They can work inside the cell, or they can be secreted.

I hope that helps!Source:I took AP bio 00 CommentOther Answers (2)Relevance Daksha Danswered6 years agoMaking EnzymesAs long as a cell's membrane is intact and it is making all of the enzymes it needs to function properly, the cell is alive. The enzymes it needs to function properly allow the cell to create energy from glucose, construct the pieces that make up its cell wall, reproduce and, of course, produce new enzymes.

So where do all of these enzymes come from? And how does the cell produce them when it needs them? If a cell is just a collection of enzymes causing chemical reactions that make the cell do what it does, then how can a set of chemical reactions create the enzymes it needs, and how can the cell reproduce? Where does the miracle of life come from?

The answer to these questions lies in the DNA, or deoxyribonucleic acid. You have certainly heard of DNA, chromosomes and genes. DNA guides the cell in its production of new enzymes.

The DNA in a cell is really just a pattern made up of four different parts, called nucleotides or bases. Imagine a set of blocks that has only four different shapes, or an alphabet that has only four different letters. DNA is a long string of blocks or letters. In an E. coli cell, the DNA pattern is about 4 million blocks long. If you were to stretch out this single stand of DNA, it would be 1.36 mm long -- pretty long considering the bacteria itself is 1,000 times smaller. In bacteria, the DNA strand is like a wadded-up ball of string. Imagine taking 1,000 feet (300 meters) of incredibly thin thread and wadding it up -- you could easily hold it in your hand. [A human's DNA is about 3 billion blocks long, or almost 1,000 times longer than an E. coli's. Human DNA is so long that the wadded-up approach does not work. Instead, human DNA is tightly wrapped into 23 structures called chromosomes to pack it more tightly and fit it inside a cell.]

The amazing thing about DNA is this: DNA is nothing more than a pattern that tells the cell how to make its proteins! That is all that DNA does. The 4 million bases in an E. coli cell's DNA tell the cell how to make the 1,000 or so enzymes that an E. coli cell needs to live its life. A gene is simply a section of DNA that acts as a template to form an enzyme.

Let's look at the entire process of how DNA is turned into an enzyme so you can understand how it works.

I think the first part is the most important.

If you want find out more go on this website.

http://science.howstuffworks.com/cell5.h...

By what process are Enzymes made in the cell?I know that enzymes are produced by living cells with each cell containing about several hundred enzymes. I am just curious to know by what process are enzymes are made in the cell?Best AnswerAsker's Choice

lippy19850528answered8 years ago The general idea of how enzyme is made in the cell can be considered as follow:enzyme is made of proteins and proteins are made of many individual amino acids connected by peptide bond N-C=O. thus protein can be known as chain of amino acids.the synthesis of protein is controlled within the nucleus through gene regulation, and the DNA is what codes for the order of amino acid in a protein chain. there are many genes which codes for different protein hence enzyme, some enzymes do consist of more than one polypeptide chain thus eptistacy can act on such enzyme. it will be quite difficult for you to understand about the process detail without any background knowledge in genetics, but i stil tell you the simplified version, for example the synthesis of enzyme A, a piece of DNA contains numerous bases attached to a sugar phosphate backbone and each 3 bases codes for one amino acid, there are 4 bases (adenine, tymine, cytosine and guanine) for example CUG codes for the amino acid leucine. this piece of DNA is transcribed into mRNA for which thymine becomes uracil, the mRNA is translocated into the cytosol from the nucleus to the rough endoplasmic reticulum where ribosomes will attached to the mRNA and start the synthesis of the enzyme, the start codon AUG coding for amino acid methionine will be recognised by tRNA with anticodon 3'UAC5' since than base A will base pair with base U and base C with base pair with G. the tRNA is responsible for assembling the amino acids into a chain, one the protein is complete it will than leaves the RER and send to the place inside the cell where it's needed via vesicle. If you really want to understand how enzyme is synthesised, you should be reading a book.^^Source:My brainAsker's rating & comment

Just what I was looking for. Thorough and infomative,... Thanks! 20 CommentOther Answers (3)Relevance Kishanswered8 years agoenzymes are essentially complex proteins. proteins are formed in living cells by the process of translation and then transcription.

translation is the process of forming a messenger-RNA from part of the DNA that codes for the production of the protein. it takes place in the nucleus. the m-RNA formed leaves the nucleus via the nuclear pore into the cytoplasm of the cell where translation takes place.

translation is the process where proteins are formed from m-RNA and amino acids that are found freely-floating in the cytoplasm. this process also requires ribosomes that are either found freely-floating in the cytoplasm or the ones that are membrane bound to the smooth endoplasmic reticulum.

at the end of translation, a protein strand is formed. the protein next enters the golgi apparatus where they get modified and made more complex. some become glycoproteins while other gets lipids attached to them forming lipoproteins. it is here where proteins that are destined to be enzymes accquire their specific shape and structure that is characteristic of an enzyme.

the enzyme that is now formed leaves the golgi apparatus in a vesicles that gets transfered through the cytoplasm where it fuses with the cell membrane of the cell and releases the enzyme out of the cell via exocytosis.

some enzymes of course are used within a cell itself. in this case the vesicle that contains the enzyme will fuse with another vesicle that contains the matter that needs to be digested.

this is of course a really watered down version. the detailed steps for translation, transcription, modification and transport out of the cell via exocytosis are explained further in the links below.

http://en.wikipedia.org/wiki/Transcripti...http://en.wikipedia.org/wiki/Translation...http://en.wikipedia.org/wiki/Golgi_appar...http://en.wikipedia.org/wiki/Exocytosis

hope this helped though!

Where does protein and enzyme synthesis take place?Hi guys, Im wondering about this question just for the sake of it. I appreciate your help on helping me solve it. Thank you.Best Answer

unhrdofanswered8 years ago Enzymes are a type of protein, so they are made at the same place.

Protein and Enzyme synthesis take place in cells through translation. With translation, DNA in the nucleus is unraveled to make mRNA. This mRNA leaves the nucleus and goes out into the cell where tRNA is made from the mRNA. The mRNA has a series of codons (3 nucleotides per amino acid). Amino acids are the building blocks of proteins. The tRNA makes anticodons that match with amino acids in the cell. This occurs at cellular organelles called ribosomes. The amino acids link together to form chains through peptide bonds.

There are 4 levels of structure that proteins have.

Primary: Amino acid chainSecondary: The chain folds and spirals into alpha helices and beta sheets.Tertiary: These spirals and folds coil through other bonds such as sulphide bonds.Quaternary: Multiple groups of these chains combine to create a protein.

I hope that this helped. 00 CommentOther Answers (6)Relevance CBRRideranswered8 years agoProtein synthesis takes place on the ribosomes.

Enzymes are essentially proteins which act as a biological catalyst to speed up chemical reactions, it is synthesized the same as the proteins. 00 Comment gibbie99answered8 years agoNone of these answers are totally correct, yes protein translation occurs in ribosome, but ribosomes exist both in the cytoplasm and the rough endoplasmic reticulum (RER). 00 Comment jawajamesanswered8 years agoProteins are synthesized on ribosomes, either free floating in the cytosol, or attached to the endoplasmic reticulum. 00 Comment St. Judy's cometanswered8 years agoYes it does happen on the ribosomes but they are physically located in the cytosol. 00 Comment mizanswered8 years agoPROTEIN SYNTHESIS: TRANSLATION

takes place in ribosomes IN CYTOPLASM

2. What are Enzymes...An enzyme is a protein that acts as a catalyst. The enzyme is responsible for accelerating the rate of a reaction in which various substrates are converted to products through the formation of an enzyme-substrate complex. In general, each type of enzyme catalyzes only one type of reaction and will operate on only one type of substrate. This is often referred to as a "lock and key" mechanism. As a consequence, enzymes are highly specific and are able to discriminate between slightly different substrate molecules. In addition, enzymes exhibit optimal catalytic activity over a narrow range of temperature, ionic strength and pH

General characteristics of enzymes1. Enzymes work very rapidly One molecule of enzyme can turn thousands or millions of substrate molecules into products per minute. For example, catalyse can transform approximately six million hydrogen peroxide molecules into oxygen and water molecules per minute.2. Enzymes are not destroyed by the reactions which that catalyse Since enzymes are not altered by the reactions they catalysed, they can be used again. A smaill concentration of enzymes can bring about a large amount of biochemical reactions3. Enzyme-catalysed reactions are reversible lactose + water lactase> glucose + galactose lactose + water enzyme+product The explanation of enzyme action is known as the lock and key hypothesis, where the substrate is like a key whose shape is complementary to the enzyme or lock. The lock and key hypothesis is able to explain why enzymes are specific and why any change in enzyme shape alters its effectiveness.

The production of extracellular enzymes

In the nucleus, the DNA double helix unwinds & exposes its two strands for the synthesis of mRNA strand.The mRNA (messenger RNA) leaves the nucleus through the nuclear pore and moves to a ribosome.The mRNA attaches itself to the ribosome.Proteins are synthesised & transported through the space within the rough ER.Proteins depart from rough ER wrapped in vesicles (transport vesicle) that bud off from the membrane.The transport vesicle then fuse with Golgi apparatus. The proteins are further modified, packaged, sorted (eg. carbohydrates are added to proteins --> glycoproteins)Secretory vesicles then bud off from the Golgi apparatus & travel to plasma membrane.They then diffuse with the plasma membrane before being released outside.he role of enzymes in organisms

Metabolisms are chemical reactions that occur within a living organism.Enzymes regulate almost all the cellular reactions.Enzymes are biological catalysts that speed up biochemical reactions in the cell.

The general

1.

Naming of enzymes

1.The name of enzyme is derived from the name of the substrate it catalyses.2.The name of most enzymes are derived by adding suffix ase to the name of the substrates they hydrolyse. For example:

SubstrateEnzyme

LactoseLactase

SucroseSucrase

Lipidlipase

3.However, there are some enzymes that were named before a systematic way of naming enzymes was formulated. For example, pepsin, trypsin and rennin.

Synthesis of enzymes

1.Ribosomes are the sites of protein synthesis. Since enzymes are proteins, ribosomes are also the sites of enzymes synthesis.2.The information for the synthesis of enzymes is carried by the DNA. The different sequences of bases in the DNA are codes to make different proteins. During the process, messenger RNA is formed to translate the codes into a sequence of amino acids. These amino acids are bonded together to form specific enzymes according to DNAs codes.

Intracellular enzymes and extracellular enzymes

1.Enzymes are synthesised by specific cells.2.Enzymes which are produced and retained in the cell for the use of the cell itself are called intracellular enzymes. These enzymes are found in the cytoplasm, nucleus, mitochondria and chloroplasts. For example, the enzymes oxireductase catalyses biological oxidation and reduction in mitochondria.3.Enzymes which are produced in the cell but secreted from the cell to function externally are called extracellular enzymes. For example, digestive enzymes produced by the pancreas are not used by the cell in the pancreas but are transported to the duodenum, which is the actual site of the enzymatic reaction.

Production of extracellular enzymes

1.Many enzymes produced by specialised cells are secreted outside the cell. For example, pancreatic cells secrete pancreatic amylase outside the cells to be transported to the target organ (duodenum).

The production of extracellular enzymesa.The nucleus contains DNA which carries the information for the synthesis of enzymes.b.Protein that are synthesised at the ribosomes are transported through the space within the rough endoplasmic reticulum (rough ER).c.Proteins depart from the rough ER wrapped in vesiscles that bud off from the membranes of the rough ER.d.These transport vesicles then fuse with the membrane of the Golgi apparatus and empty their contents into the membranous space.e.The proteins are further modified during their transport in the Golgi apparatus, for example, carbohydrates are added to protein to make glycoproteins.f.Secretory vesicles containing these modified proteins bud off from the Golgi apparatus and travel to the plasma membrane.g.These vesicles will then fuse with the plasma membrane before releasing the protein outside the cell as enzymes.

Mechanism of enzyme action

1.Each enzyme molecule has a region with a very precise shape called the active site.2.The substrate molecule fits into the active site of the enzyme like a key into a lock.3.Various types of bonds including hydrogen bonds and ionic bonds hold the substrate(s) in the active site to form an enzyme-substrate complex.4.The enzyme then changes the substrate(s) either by splitting it apart (as in hydrolysis) or linking them together (as in condensation).5.Once formed, the products no longer fit into the active site and escape into the surrounding medium, leaving the active site free to receive other substrate molecule.

Enzyme + substrateenzyme-substrate complexenzymes + products

6.The explanation of enzyme action is known as the lock and key hypothesis, where the substrate is like a key whose shape is complementary to the enzyme or lock.7.The lock and key hypothesis is able to explain:a.why enzymes are specific, andb.why any change in the shape of enzyme alters its effectiveness.

1. SITES OF ENZYME SYNTHESIS o Enzymes are synthesized by ribosomes which are attached to the rough endoplasmic reticulum. o Information for the synthesis of enzyme is carried by DNA. o Amino acids are bonded together to form specific enzyme according to the DNAs codes.2. INTRACELLULAR AND EXTRACELLULAR ENZYMES o o o 3. Intracellular enzymes are synthesized and retained in the cell for the use of cell itself. 4. They are found in the cytoplasm, nucleus, mitochondria and chloroplast. Example : Oxydoreductase catalyses biological oxidation. Enzymes involved in reduction in the mitochondria. Extracellular enzymes are synthesized in the cell but secreted from the cell to work externally. Example : Digestive enzyme produced by the pancreas, are not used by the cells in the pancreas but are transported to the duodenum.

What is enzyme? What are enzymes?Enzymes areproteinsthat are alsobiological catalystsSome of the characteristics of enzymes: They are proteins They are biological catalysts Catalysts are substances that are used to speed up the rates of chemical reactions by lowering the activation energy. They are not changed at the end of the reaction Enzymes will remain unchanged during a reaction Enzymes of substrate specific Substrates are substances that typically apart of the starting materials of a reaction. They are what enzymes act upon. The substrate binds onto theactive siteof the enzyme that is specific to the substrate.

Making EnzymesAds by GoogleNeed Help Losing Weight?100% Natural Drink To Lose Weight Reduce Body Weight Without Rebound!www.s-recipes.com/Weight-LossHow To Publish A Book?Get Your Free Book Publishing Guide And Be a Published Author in 2014.partridgepublishing.com/Singapore6 Reasons God ExistsNo Arm-Twisting. Straightforward. Compelling Evidences. You Decide.everystudent.comAs long as a cell's membrane is intact and it is making all of the enzymes it needs to function properly, the cell isalive. The enzymes it needs to function properly allow the cell to create energy from glucose, construct the pieces that make up its cell wall, reproduce and, of course, produce new enzymes.So where do all of these enzymes come from? And how does the cell produce them when it needs them? If a cell is just a collection of enzymes causing chemical reactions that make the cell do what it does, then how can a set of chemical reactions create the enzymes it needs, and how can the cell reproduce? Where does the miracle of life come from?The answer to these questions lies in theDNA, or deoxyribonucleic acid. You have certainly heard of DNA,chromosomesandgenes. DNA guides the cell in its production of new enzymes.The DNA in a cell is really just a pattern made up of four different parts, callednucleotidesorbases. Imagine a set of blocks that has only four different shapes, or an alphabet that has only four different letters. DNA is a long string of blocks or letters. In an E. coli cell, the DNA pattern is about 4 million blocks long. If you were to stretch out this single stand of DNA, it would be 1.36 mm long -- pretty long considering the bacteria itself is 1,000 times smaller. In bacteria, the DNA strand is like a wadded-up ball of string. Imagine taking 1,000 feet (300 meters) of incredibly thin thread and wadding it up -- you could easily hold it in your hand. [A human's DNA is about 3 billion blocks long, or almost 1,000 times longer than an E. coli's. Human DNA is so long that the wadded-up approach does not work. Instead, human DNA is tightly wrapped into 23 structures calledchromosomesto pack it more tightly and fit it inside a cell.]The amazing thing about DNA is this: DNA is nothing more than a pattern that tells the cell how to make its proteins! That is all that DNA does. The 4 million bases in an E. coli cell's DNA tell the cell how to make the 1,000 or so enzymes that an E. coli cell needs to live its life. Ageneis simply a section of DNA that acts as a template to form an enzyme.Let's look at the entire process of how DNA is turned into an enzyme so you can understand how it works

Page 5 6 7 8

Image courtesyU.S. Department of Energy Human Genome ProgramDNAYou have probably heard of the DNA molecule referred to as the "double-helix." DNA is like two strings twisted together in a long spiral.DNA is found in all cells asbase pairsmade of four differentnucleotides. Each base pair is formed from two complementary nucleotides bonded together. The four bases in DNA's alphabet are: Adenine Cytosine Guanine ThymineAdenine and thymine always bond together as a pair, and cytosine and guanine bond together as a pair. The pairs link together like rungs in a ladder:

Base pairs in DNA bond together to form a ladder-like structure. Because bonding occurs at angles between the bases, the whole structure twists into a helix.In an E. coli bacterium, this ladder is about 4 million base pairs long. The two ends link together to form a ring, and then the ring gets wadded up to fit inside the cell. The entire ring is known as thegenome, and scientists have completely decoded it. That is, scientists know all 4 million of the base pairs needed to form an E. coli bacterium's DNA exactly. Thehuman genome projectis in the process of finding all 3 billion or so of the base pairs in a typical human's DNA. 7 8 9

A gene consists of a promoter, the codons for an enzyme and a stop codon. Two genes are shown above. The long strand of DNA in an E. coli bacterium encodes about 4,000 genes, and at any time those genes specify about 1,000 enzymes in the cytoplasm of an E. coli cell. Many of the genes are duplicates.The Big QuestionYou may remember from a previous section that enzymes are formed from 20 different amino acids strung together in a specific order. Therefore the question is this: How do you get from DNA, made up of only four nucleotides, to an enzyme containing 20 different amino acids? There are two answers to this question:1. An extremely complex and amazing enzyme called aribosomereads messenger RNA, produced from the DNA, and converts it into amino-acid chains.2. To pick the right amino acids, a ribosome takes the nucleotides in sets of three to encode for the 20 amino acids.What this means is that every three base pairs in the DNA chain encodes for one amino acid in an enzyme. Three nucleotides in a row on a DNA strand is therefore referred to as acodon. Because DNA consists of four different bases, and because there are three bases in a codon, and because 4 * 4 * 4 = 64, there are 64 possible patterns for a codon. Since there are only 20 possible amino acids, this means that there is some redundancy -- several different codons can encode for the same amino acid. In addition, there is astop codonthat marks the end of a gene. So in a DNA strand, there is a set of 100 to 1,000 codons (300 to 3,000 bases) that specify the amino acids to form a specific enzyme, and then a stop codon to mark the end of the chain. At the beginning of the chain is a section of bases that is called apromoter. A gene, therefore, consists of a promoter, a set of codons for the amino acids in a specific enzyme, and a stop codon. That is all that a gene is.To create an enzyme, the cell must firsttranscribethe gene in the DNA intomessenger RNA. The transcription is performed by an enzyme calledRNA polymerase. RNA polymerase binds to the DNA strand at the promoter, unlinks the two strands of DNA and then makes a complementary copy of one of the DNA strands into an RNA strand. RNA, orribonucleic acid, is very similar to DNA except that it is happy to live in a single-stranded state (as opposed to DNA's desire to form complementary double-stranded helixes). So the job of RNA polymerase is to make a copy of the gene in DNA into a single strand of messenger RNA (mRNA).The strand of messenger RNA then floats over to aribosome, possibly the most amazing enzyme in nature. A ribosome looks at the first codon in a messenger RNA strand, finds the right amino acid for that codon, holds it, then looks at the next codon, finds its correct amino acid, stitches it to the first amino acid, then finds the third codon, and so on. The ribosome, in other words, reads the codons, converts them to amino acids and stitches the amino acids together to form a long chain. When it gets to the last codon -- the stop codon -- the ribosome releases the chain. The long chain of amino acids is, of course, an enzyme. It folds into its characteristic shape, floats free and begins performing whatever reaction that enzyme performs.

ADS BY GOOGLEWe Want Malaysian AuthorsStart Publishing Your Book. Get A Free Book Publishing Guide Now!partridgepublishing.com/SingaporeJobs in PetronasFind Jobs in Companies Submit Resume to Apply Nowmonster.com.mySPM Revision Guide 2014Spot Questions, Past Year Question Analysis. Download A Free Copy Nowafterschool.my/spm2014No Simple TaskObviously, the process described on the previous page is not a simple one. A ribosome is an extremely complex structure of enzymes and ribosomal RNA (rRNA) bonded together into a large molecular machine. A ribosome is helped by ATP, which powers it as it walks along the messenger RNA and as it stitches the amino acids together. It is also helped bytransfer RNA(tRNA), a collection of 20 special molecules that act as carriers for the 20 different individual amino acids. As the ribosome moves down to the next codon, the correct tRNA molecule, complete with the correct amino acid, moves into place. The ribosome breaks the amino acid off the tRNA and stitches it to the growing chain of the enzyme. The ribosome then ejects the "empty" tRNA molecule so it can go get another amino acid of the correct type.As you can see, inside every cell there are a variety of processes keeping the cell alive: There is an extremely long and very precise DNA molecule that defines all of the enzymes the cell needs. There are RNA polymerase enzymes attaching to the DNA strand at the starting points of different genes and copying the DNA for the gene into an mRNA molecule. The mRNA molecule floats over to a ribosome, which reads the molecule and stitches together the string of amino acids that it encodes. The string of amino acids floats away from the ribosome and folds into its characteristic shape so it can start catalyzing its specific reaction.The cytoplasm of any cell is swimming with ribosomes, RNA polymerases, tRNA and mRNA molecules and enzymes, all carrying out their reactions independently of each other.As long as the enzymes in a cell are active and all of the necessary enzymes are available, the cell is alive. An interesting side note: If you take a bunch of yeast cells and mistreat them (for example, place them in a blender) to release the enzymes, the resulting soup will still do the sorts of things that living yeast cells do (for example, produce carbon dioxide and alcohol from sugar) for some period of time. However, since the cells are no longer intact and therefore are not alive, no new enzymes are produced. Eventually, as the existing enzymes wear out, the soup stops reacting. At this point, the cells and the soup have "died."PrintCitation & DateFeedback

1. An enzyme or any other protein that is destined to be exported out of the cell, is made on the ribosomes that are attached to the membranes of the rough endoplasmic reticulum (RER).

2. As they are being made, the protein molecules pass through pores in the RER membranes, into the cisterns (spaces) of the RER.

3. Inside the RER, the enzymes are packaged into vesicles, which then pinch off the membranes and are carried along cytoskeleton filaments to the Golgi.

4. The vesicles fuse with the membranes of the Golgi bodies, dumping the enzyme molecules into the cisterns of the Golgi.

5. In the Golgi, the enzyme molecules are chemically labeled and sorted into other vesicles.

6. These new vesicles pinch off from the Golgi and are carried along cytoskeleton filaments to the plasmalemma (cell membrane).

7. These vesicles fuse with the plasmalemma in such a way that the enzyme molecules are dumped outside the cell.

8. This is secretion of the enzymes, which are now extracellular.

9. This is what happens to pepsin, for example, which functions in the lumen (space) of the stomach after being secreted by cells of the stomach lining.