Molecular basis of heredity. Realization of hereditary information.

Pryvrotska Iryna

Lecture questions

1. Proteins are the main living things.2. Types of proteins .3. Lipoproteins and Glycoproteins.4. Nucleotides and Nucleic Acids.5. Protein synthesis. - Transcription - Translation

Protein functions enzymes are only one class of proteins. proteins also form the scaffolding, or

structure, of a good deal of tissue; active in transporting molecules

from one site to another; they allow muscles to contract and

cells to move; some hormones are made from them

Proteins are prime examples of the building-block type of molecule.

The monomers in this case are called amino acids.

String an arbitrary number of them together in a chain—and you have a polypeptide;

when the polypeptide folds up in a specific three-dimensional manner, you have a protein.

As a practical matter, proteins are likely to be made of hundreds of amino acids strung together and folded up

Shape is critical to functioning of all proteins

Types of proteins Enzymes -Quicken chemical reactions (surcease

brocks sugar to glucose and fructose) Hormones - chemical messengers (growth hormone) Transport –move other molecules (hemoglobin) Contractive –movement (myosin and actin -allow

muscles to contract) Protective - healing, defense against invader

(fibrinogen: stops bleeding antibodies: kill bacterial invaders)

Structural –mechanical support (keratin: hair collagen: cartiilage)

Storage - stores nutrients (ovalbumin: egg white: used as nutrient for embryos)

Toxins - defense, predations (bacterial diphteria toxin)

Communication – cell signaling (glicoprotein: receptors on cell surface)

Simple proteinsConsist from only polypeptide chains

Consist from polypeptide chains and nonprotein components

Lipoproteins -are a combination of lipids and proteins; they are active in transporting fat molecules throughout the body via the bloodstream. They amount to a capsule of protein surrounding a globule of fat.

Large proteins

Large proteins

Glycoproteins are combinations of proteins and carbohydrates.

Most receptors are usually glycoproteins, meaning mostly protein with a side-chain made of carbohydrate.

Large proteins

• Chromosomes- combination of nucleic acids and proteins

Fibrous (insoluble in water) –

structural: hair, cartilage

Globular (soluble in water)

–chemical: enzymes, antibodies, receptors.

Nucleic acids there are 2 types of nucleic acids: DNA

(deoxyribonucleic acid) and RNA (ribonucleic acid).

DNA Provides Information for the Structure of Proteins

Structure DNA RNA

Sugar Deoxyribose Ribose

Bases Adenine, guanine, thymine, cytosine

Adenine, guanine, uracil, cytosine

Strands Double-stranded with base pairing

Single-stranded

Helix Yes No

DNA Basics:

1. Located in nucleus, packaged into chromosomes

• Organelles (mitochondria, chloroplasts) have their own chromosomes

2. DNA is double stranded, present in the form of a double helix

3. Bases make up complementary base pairs

Nucleic acids The nucleic acids are

polymers of smaller units called nucleotides.

A nucleotide consist of: 1) five-carbon sugar

(deoxyribose in DNA and ribose in RNA);

2) a phosphate group (PO4);

3) one of five types nitrogen-containing compounds called nitrogenous bases.

Nucleic acids

The nitrogenous bases are: Purines, which are larger –

Adenine (A), Guanine (G); Pyramidines, which are

smaller – Thymine (T), Cytosine (C), Uracil (U).

Nucleic acids The sugar and phosphate

components of the nucleotides link up to form the outer "rails" of the DNA molecule, while the bases point toward the molecule's interior.

Two chains of nucleotides are linked, via hydrogen bonds, to form DNA's double helix.

Two of these chains then link together—as if a ladder, split down the middle, were coming together—forming the most famous molecule in all of biology, the DNA double helix.

Nucleic acids

A gene is generally a collection of DNA nucleotides that contains the instructions for an individual protein.

A player in this series of steps protein synthesis is another nucleic acid, ribonucleic acid or RNA, which is involved in ferrying the DNA-encoded instructions to the sites in the cell where proteins are put together.

RNA –a polymer of ribose-containing

nucleotides, with forms single-strand. Messenger RNA carries the genetic code to the cytoplasm to

direct protein synthesis. 1. This single-stranded molecule (hundreds to thousands of

nucleotides). 2. mRNA contains codons that are complementary to the DNA

codons from which it was transcribed Transfer RNA is folded into a cloverleaf shape and contains about

80 nucleo tides. 1. Each tRNA combines with a specific amino acid that has been

activated by an enzyme. 2. One end of the tRNA molecule possesses an anticodon, a

triplet of nucleotides that recognizes the complementary codon in mRNA.

Ribosomal RNA associates with many different proteins (including enzymes) to form ribosomes.

1. rRNA associates with mRNA and tRNA during protein synthesis. 2. rRNA synthesis takes place in the nucleolus and is catalyzed by

RNA polymerase.

Most Genes encode proteins

DNA mRNA protein

DNA is copied into RNA via transcription

The Genetic Code is universal

DNA replication

1. DNA helicase (enzyme) unwinds the DNA. The junction between the unwound part and the open part is called a replication fork.

2. DNA polymerase adds the complementary nucleotides and binds the sugars and phosphates. DNA polymerase travels from the 3' to the 5' end.

DNA replication

3. DNA polymerase adds complementary nucleotides on the other side of the ladder. Traveling in the opposite direction.

4. One side is the leading strand - it follows the helicase as it unwinds.

5. The other side is the lagging strand - its moving away from the helicase

DNA replication

Problem: it reaches the replication fork, but the helicase is moving in the opposite direction. It stops, and another polymerase binds farther down the chain.

This process creates several fragments, called Okazaki Fragments, that are bound together by DNA ligase.

DNA replication 6. During replication, there are many points

along the DNA that are synthesized at the same time (multiple replication forks). It would take forever to go from one end to the other, it is more efficient to open up several points at one time.

All organisms use the same genetic codeEach set of three nucleotides codes for an amino acid = “The Genetic Code”

The genetic code

consists of 64 triplet codons (A, G, C, U) 43 = 64

all codons are used in protein synthesis 20 amino acids 3 termination (stop) codons: UAA, UAG, UGA AUG (methionine) is the start codon (also used

internally) multiple codons for a single amino acid =

degeneracy Genetic code is unambiguous. Each triplet codon

has only one meaning 5 amino acids are specified by the first two

nucleotides only

3 additional amino acids (Arg, Leu, and Ser) are specified by six different codons

Accuracy of Replication

The mismatched nucleotide causes a pause in replication, and the mismatched nucleotide is excised from the daughter strand.

The errors that slip through nucleotide selection and proofreading cause a gene mutation to occur.

Actually it is of benefit for mutations to occur occasionally because variation is the raw material for the evolutionary process.

Point Mutations Point mutations involve a change in

a single nucleotide and therefore a change in a specific codon.

When one base is substituted for another, the results can be variable. For example, if UAC is changed to UAU, there is no noticeable effect, because both of these codons code for tyrosine. Therefore, this is called a silent mutation.

Point Mutations

If UAC is changed to UAG(stop codon.

If this substitution occurs early in the gene, the resulting protein may be too short and may be unable to function. Such an effect is called a nonsense mutation.

Point Mutations

Finally, if UAC is changed to CAC, then histidine is incorporated into the protein instead of tyrosine. This is a missense mutation.

Point Mutations The term reading frame applies to the

sequence of codons because they are read from some specific starting point as is this sentence:

THE CAT ATE THE RAT. If the latter C is deleted from this sentence and the reading frame is shifted,

THE ATA TET HER AT –something that doesn't make sence.

That call frameshift mutations.

Gene Expression The process by which a gene produces a product,

usually a protein, is called gene expression. DNA not only serves as a template for its own

replication, it is also a template for RNA formation. Gene Expression in prokaryotes: transcription, translation. Gene Expression in eukaryotic cells: transcription, processing, translation.

Transcription

It is the first step required for gene expression.

During transcription, a mRNA molecule is formed that has a sequence of bases complementary to a portion of one DNA strand;

A, T, G, or С is present in the DNA template,

U, A, C, or G is incorporated into the mRNA molecule

The process by which a mRNA copy is made of a portion of DNA is called transcription

Transcription Transcription begins at a region of DNA called a

promoter. A promoter is a special sequence of DNA bases

where RNA polymerase attaches and the transcribing process begins. A promoter is at the start end of the gene to be transcribed.

Elongation of the mRNA molecule occurs as long as transcription proceeds. Finally, RNA polymerase comes to a terminator sequence at the other end of the gene being transcribed.

The terminator causes RNA polymerase to stop transcribing the DNA and to release the mRNA molecule, now called a RNA transcript

RNA Processing Special molecular splicing complexes cut out sections of

introns. Then the remaining portions of the mRNA tape are spliced together.

exons: portions of the mRNA transcript that code for amino acids.

From this, it follows that introns are noncoding portions of the original mRNA tape; they do not contain information for the sequencing of amino acids in a protein.

Translation

During translation, the sequence of codons in mRNA directs the sequence of amino acids in a protein.

Two other types of RNA are needed for protein synthesis.

rRNA is contained in the ribosomes, where the codons of mRNA are read

tRNA carries amino acids to the ribosomes so that protein synthesis сan occur.

The steps of translation.

mRNA Binds to Ribosome; Polypeptide Chain Is

Elongated Termination of the Growing

Chain

The steps in translation are: The ribosome binds to mRNA at a specific area.

The ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence.

Each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain.

The ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA.

The polypeptide forms into its native shape and starts acting as a functional protein in the cell

Regulation of Gene expression lac operon in E. Coli

Function - to produce enzymes which break down lactose (milk sugar) when lactose is present, they turn on and produce enzymes

Two components - repressor genes and functional genes Promoter (P) - aids in RNA polymerase binding Operator (O) - "on/off" switch - binding site for the

repressor protein Repressor (lacI) gene

Repressor gene (lacI) - produces repressor protein w/ two binding sites, one for the operator and one for lactose

The repressor protein is under allosteric control - when not bound to lactose, the repressor protein can bind to the operator

When lactose is present, an isomer of lactose, allolactose, will also be present in small amounts.  Allolactose binds to the allosteric site and changes the conformation of the repressor protein so that it is no longer capable of binding to the operator

Operation - If lactose is not present:the repressor gene produces repressor, which binds to the operator. This blocks the action of RNA polymerase, thereby preventing transcription

Thank You for attention!

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