Chapter 11: DNA & Genes Sections 11.1: DNA: The Molecular of Heredity Subsections: What is DNA? Replication of DNA

Chapter 11: DNA & GenesSections 11.1: DNA: The Molecular of Heredity

Subsections:What is DNA?

Replication of DNA

What is DNA?DNA as the genetic

material

Enzymes are critical for an organism’s function because they control the chemical reactions for life.DNA contains the informationto produce proteins that make enzymes.Hershey & Chase: proved that DNA is the genetic material

The structure of nucleotides

DNA is composed of three parts:Phosphate groupSugar group (deoxyribose)Nitrogenous bases (4 types)

Phosphate group and sugar group form the backbone of DNA molecule.

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A nitrogenous base is a carbon ring structure thatcontains one or more atoms of nitrogen.

In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

Adenine (A) Guanine (G) Thymine (T)Cytosine (C)

The structure of nucleotidesThe structure of nucleotides

What is DNA?

What is DNA?The structure of DNA

The importance of nucleotide sequences

Four nitrogenous bases:AdenineGuanineCytosyineThymine

Are attached by hydrogen and covalent bonds to opposite and adjacent nucleotides.

Watson & Crick:Discovered the structureof DNA to be double stranded that form a helix shape hence double helix.


DNA is a polymer made of repeating subunitscalled nucleotides.

Nucleotides have three parts: a simple sugar,a phosphate group, and a nitrogenous base.

Phosphate group

Sugar (deoxyribose)

Nitrogenous base

The structure of DNAThe structure of DNA


The importance of nucleotide sequencesThe importance of nucleotide sequences

Chromosome

The sequence of nucleotides forms the unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be.

Replication of DNAHow DNA replicates

Interphase:Prior to mitosis and meiosis, the DNA replicates during the S phase of interphase.The DNA is copied to have Two sets of identical DNA.Refer to page 285 Figure 11.4.

Copying DNA

• Refer to page 286-287 Figure 11.5

• DNA is copied prior to mitosis and meiosis.

Replication of DNAPart A:

Separation of strandsWhen a cell begins to copy its DNA, the two nucleotide strands of a DNA molecule separate when the hydrogen bonds connecting the base pairs are broken. As the DNA molecule unzips, the bases are exposed. Caused by an enzyme .

Part B: Base Pairing

The bases in the free nucleotides pair with exposed bases in the DNA strand. Thymine combines with adenine. Cytosine combines with guanine. All bases pairs have a hydrogen bonds to complete the pairing.


In DNA, the amount of adenine is always equal to the amount of thymine, and the amount of guanine is always equal to the amount of cytosine.

Part B: Base PairingsPart B: Base Pairings

Replication of DNAPart C:

Bonding of basesThe sugar (deoxyribose) and the phosphate parts of adjacent nucleotides bond together with covalent bonds (share electrons) to form the backbone of the new strand. Each original strand is now hydrogen-bonded to a new strand.

Part D: Results of replication

The process of replication produces two molecules of DNA. Each new molecule has one strand from the original molecule and one strand that has been newly synthesized from the free nucleotides in the cell.

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Replication of DNA during S step the of cell cycle

Replication of DNA during S step the of cell cycle

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Chapter 11: DNA & GenesSections 11.2: From DNA

to ProteinSubsections:

Genes and Proteins, RNA, Transcription, RNA processing, The Genetic Code, &

Translation

Two Subsections:Genes and

Proteins

Refer to attachment or next slide.

RNAThree differences Between RNA & DNA

Three types of RNAMessenger – mRNARibosome – rRNATransfer - tRNA


Some proteins become important structures,such as the filaments in muscle tissue.

Other proteins, such as enzymes, control chemical reactions that perform key life functions—breaking down glucose molecules in cellular respiration, digesting food, or making spindle fibers during mitosis.

Genes and ProteinsGenes and Proteins


RNA like DNA, is a nucleic acid. RNA structure differs from DNA structure in three ways.

First, RNA is single stranded—it looks likeone-half of a zipper —whereas DNA is double stranded.

RNA: three difference compared to DNARNA: three difference compared to DNA


Second, the sugar in RNA is ribose; DNA’s sugar is deoxyribose.

Ribose

RNA: three differences compared to DNARNA: three differences compared to DNA


Third, both DNA and RNA contain four nitrogenous bases, but rather than thymine, RNA contains a similar base called uracil (U).

Uracil forms a base pair with adenine in RNA, just as thymine does in DNA.

Uracil

Hydrogen bonds

Adenine

RNA: three differences compared to DNARNA: three differences compared to DNA


There are three types of RNA thathelp build proteins.

Messenger RNA (mRNA), bringsinstructions from DNA in the nucleus to the cell’s factory floor, the cytoplasm. In nucleus and cytoplasm.

RNA: three types of RNARNA: three types of RNA


The ribosome, made of ribosomalRNA (rRNA), binds to the

mRNA and uses the instructions to assemble the amino acids in the correct order. Located in cytoplasm only.



Transfer RNA (tRNA) is the supplier. Transfer RNA delivers amino acids to the ribosome to be assembled into a protein. Located in the cytoplasm only.


Amino Acid

Transfer RNA

anti-CODONS


Transcription: copy DNA to mRNA

Transcription: copy DNA to mRNA

Click on Transcription for video

http://www.youtube.com/watch?v=983lhh20rGY



Not all the nucleotides in the DNA ofeukaryotic cells carry instructions—or code—for making proteins.

Genes usually contain many long noncoding nucleotide sequences, called introns, that are scattered among the coding sequences.

RNA ProcessingRNA Processing


RNA ProcessingRNA ProcessingRegions that contain informationare called exons because they are expressed.

When mRNA is transcribed fromDNA, both introns and exons are copied.


Enzymes in the nucleus cut out theintron segments and paste the mRNA back together.

The mRNA then leaves the nucleus and travels to the ribosome.

RNA ProcessingRNA Processing


Sixty-four combinations arepossible when a sequence of three bases is used; thus, 64 different mRNA codons are in the genetic code.

The Genetic CodeThe Genetic Code



Table 11.1: The Messager RNA Gentic Code

Page 292

Some codons do not code for amino acids;they provide instructions for making the protein.

More than one codon can code for the sameamino acid.

However, for any one codon, there can beonly one amino acid.


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Translation: From mRNA to ProteinTranslation: From mRNA to Protein

The process of converting the information ina sequence of nitrogenous bases in mRNA into a sequence of amino acids in protein is known as translation.

Translation takes place at the ribosomes inthe cytoplasm.

In prokaryotic cells, which have no nucleus,the mRNA is made in the cytoplasm.

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Translation: From mRNA to ProteinTranslation: From mRNA to ProteinIn eukaryotic cells, mRNA is madein the nucleus and travels to the cytoplasm.

In cytoplasm, a ribosome attachesto the strand of mRNA like a clothespin clamped onto a clothesline.

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Each tRNA molecule attaches to only one type of amino acid.

Amino acid

Chain of RNA nucleotides

Transfer RNA

molecule

Anticondon

The role of transfer RNAThe role of transfer RNA

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Translation: mRNA to protein with

rRNA & tRNA

Translation: mRNA to protein with

rRNA & tRNA

Click on Transcription for video



Usually, the first codon on mRNA is AUG, which codes for the amino acid methionine.

AUG signals the start of protein synthesis.

When this signal is given, the ribosome slides along the mRNA to the next codon.

The role of transfer RNA (tRNA)The role of transfer RNA (tRNA)

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tRNA anticodon

Methionine


mRNA codonCopyright BDOL 2006

The amino acids are joined when a peptide bond isformed between them.

AlanineMethionine

Peptide bond


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A chain of amino acids is formed until thestop codon is reached on the mRNA strand.

Stop codon


Amino acid chain

mRNA strand

tRNA

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Follow the steps inFigure 11.9 page 294.

Translating the mRNA codeTranslating the mRNA code

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11.2 Questions1. List the three differences between RNA and

DNA2. List the three kinds or types of RNA include

the location of each type within the cell.3. Name the location of where transcription

occurs.4. What is the function of an intron?5. What is the function of an exon?

1. Name the three differences between RNA and DNA

1. RNA is single strand while DNA is double stranded – DNA is known as a double helix2. RNA is composed of RIBOSE sugar with an

extra oxygen while DNA is composed of DEOXYRIBOSE sugar with one less oxygen.

3. RNA has URACIL as a nitrogen base while DNA has THYMINE which both base pair with adenine.

2. List the three types or kinds of RNA include the locations within the cell.

1. mRNA – messenger RNA is found in the nucleus and cytoplasm of the cell.

2. rRNA – ribosomal RNA is found in the cytoplasm of the cell.

3. tRNA – transfer RNA is found in the cytoplasm of the cell.

3. Name the location of where transcription occurs.

Transcription occurs in the nucleus of the cell.

4. What is the function of an intron?

An intron is the part of the DNA and mRNA that is noncoding. The intron is cut and removed from the mRNA before leaving the nucleus.

5. What is the function of an exon?

An exon is the part of the DNA and mRNA that is coded or codon. The exon is pasted together onto the mRNA before Leaving the nucleus.

Documents

Chapter 11: DNA & Genes Sections 11.1: DNA: The Molecular of Heredity Subsections: What is DNA? Replication of DNA