molecular basis of inheritance

What is translation?

The process of polymerisation of amino acids to form a polypeptide/protein

Where does translation occur?

On ribosomes in the cytoplasm.

What determines the number and sequence of amino acids in a protein?

Genetic information present in DNA, carried to ribosomes by mRNA.

Why are ribosomes called protein-forming factories?

They join amino acids together by peptide bonds to form polypeptides

How many different amino acids are involved in protein synthesis?

20

What are the four major steps/sub-processes of translation?

A. 1. Initiation
2. Peptide bond formation & chain elongation
3. Termination
4. Post-translational processing

What is activation of amino acids also called?

. Charging.

Which molecule provides energy for amino-acid activation?

ATP

Which enzymes activate amino acids?

. Aminoacyl synthetases

How many specific aminoacyl synthetases are there?

About 20, one for each amino acid.

What is formed when an amino acid reacts with ATP and the enzyme?

An amino acid–enzyme–AMP complex (aminoacyl adenylate).

What happens to ATP during amino-acid activation?

Two inorganic phosphates are released.

What is a charged tRNA?

A tRNA carrying its specific amino acid

Why are at least 20 types of tRNA required

Each type of tRNA carries a particular amino acid.

What is the bacterial ribosome?

70S = 50S large subunit + 30S small subunit.

What is the eukaryotic ribosome?

80S = 60S large subunit + 40S small subunit.

What are the rRNA components of the bacterial 70S ribosome?

50S → 23S + 5S
30S → 16S.

What are the rRNA components of the eukaryotic 80S ribosome?

60S → 28S + 5.8S + 5S
40S → 18S.

What are the two sites of a ribosome?

A-site, P-site

What happens at the A-site?

Incoming charged tRNA binds

What happens at the P-site?

The tRNA carrying the growing polypeptide is present.

What is the initiation codon?

AUG

Which amino acid does AUG code for?

Methionine (Met).

What amino acid is present on the initiator tRNA?

Methionine (fMet in prokaryotes).

Which codon pairs with the initiator tRNA anticodon?

AUG ↔ UAC

What happens when the small ribosomal subunit binds mRNA?

It recognises and binds the initiation region/start codon.

What happens after the initiator tRNA binds AUG?

The large ribosomal subunit joins to form the initiation complex.

In which direction is mRNA read?

. 5′ → 3′.

In which direction does the polypeptide chain grow?

N-terminus → C-terminus.

What catalyses peptide bond formation?

Peptidyl transferase activity of the ribosome.

Between which groups is a peptide bond formed?

Between the amino group of one amino acid and the carboxyl group of another.

What happens after peptide bond formation?

The growing polypeptide is transferred to the tRNA in the A-site.

What is translocation?

Movement of the ribosome along mRNA by one codon in the 5′ → 3′ direction.

What happens to the tRNA at the A-site?

It shifts to the P-site carrying the growing polypeptide.

What happens repeatedly during elongation?

Codon–anticodon pairing → peptide bond formation → translocation.

What are the three termination/stop codons?

UAA, UAG and UGA.

What recognises the termination codon?

Release factors.

What happens when a release factor binds?

Hydrolysis occurs and the completed polypeptide is released.

Q42. What happens to the ribosome after termination?

The two ribosomal subunits separate.

Is a newly formed polypeptide always immediately functional?

No

Where can post-translational processing occur?

Endoplasmic reticulum and Golgi complex.

What is a polyribosome?

Several ribosomes simultaneously attached to the same mRNA

What is the advantage of a polyribosome?

allows many copies of the same protein to be produced from one mRNA.

What determines the number of ribosomes associated with an mRNA?

Mainly the length of the mRNA.

What does gene expression mean?

The process by which information in a gene is used to produce a functional product, usually a protein.

.What is regulation of gene expression?

Turning particular genes on or off according to cellular requirements.

Who proposed the one gene–one enzyme hypothesis?

Beadle and Tatum.

What organism did Beadle and Tatum study?

Neurospora crassa (pink bread mould).

What did the one gene–one enzyme hypothesis state?

One gene controls the production of one enzyme.

Why was the hypothesis later modified?

Proteins can contain multiple polypeptide chains, so it became one gene–one polypeptide

Who proposed the operon concept?

François Jacob and Jacques Monod.

What is an operon?

group of genes arranged together and regulated as a single unit.

What are structural genes?

Genes containing information for synthesis of proteins/enzymes.

What is the regulator gene?

produces the repressor protein.

What is the promoter gene/site?

he site where RNA polymerase binds to initiate transcription.

What is the operator gene?

The site where the repressor binds, controlling transcription of structural genes.

What is the lac operon?

An inducible operon controlling lactose metabolism in E. coli.

What are the three structural genes of lac operon?

z, y and a.

What does the z gene code for?

β-galactosidase

What does the y gene code for?

Permease

. What does the a gene code for?

Transacetylase

What is the inducer in the lac operon?

Lactose (more precisely, its active inducer form allolactose in the standard model).

What happens when lactose is absent?

Repressor binds the operator → RNA polymerase cannot proceed → transcription is switched off.

What happens when lactose is present?

Lactose binds the repressor → repressor cannot bind operator → transcription is switched on.

What type of regulation is lac operon?

Inducible / negative regulation.

Why is the lac operon called inducible?

Its transcription is switched on by an inducer.

What does HGP stand for?

Human Genome ProjectOct 1990

What were major goals of HGP?

Identify human genes, determine the DNA sequence, store information in databases and develop tools for data analysis.

. Approximately how many genes were estimated in the human genome?

About 25,000 in the textbook's HGP description.

What are ESTs?

Expressed Sequence Tags — sequences used to identify genes expressed as RNA.

What are BAC and YAC?

Bacterial Artificial Chromosome and Yeast Artificial Chromosome, used as cloning vectors.

Which scientist developed the DNA sequencing method used in HGP?

Frederick Sanger.

Hgp

Working draft 2000 genome sequence 2003