9.1-9.2 Flashcards by KAYLEIGH O'SULLIVAN

Genetic code is the language that allow

DNA and RNA sequences to be
translated into proteins

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Two nucleotides

4^2 = 16 possible codons

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how many amino acids

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codon

nucleotide triplet

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code is partically

redunant more than one codon per given AA

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Charles Yanofsky and Sydney Brenne

in 1960s, collected evidence that supported gene-protein colinearity
1. The length of the gene is proportional to the length of the protein
2.Consecutive nucleotides in a gene from the start to stop determine the consecutive/linear order of amino acids in a protein

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Yanofsky and his lab generated a set

Trp- auxotrophic mutants in E. coli

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Trp- auxotrophic mutants in E. coli

Mutations in trpA gene, encoding a subunit of the enzyme tryptophan synthase

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Trp- auxotrophic mutants in E. coli

Mutations in trpA gene, encoding a subunit of the enzyme tryptophan synthase

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Yanofsky was the first to

Created a fine-structure recombination map of these mutations using P1 bacteriophage and determined the amino acid sequence of the mutant tryptophan synthase

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Point mutations altering different nucleotides may affect the

SAME amino acid (missense mutations)

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A Gene’s Nucleotide Sequence is

Colinear with the Amino Acid Sequence of the Encoded Polypeptide

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Francis Crick and Sydney Brenner

In 1955, used bacteriophage T4 rIIB gene with Proflavin mutation

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Missense mutation

mutation in gene that changes a codon for one amino acid to a codon that specifies a different amino acid

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Yanofsky observed

missense mutation

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Francis Crick and Sydney Brenner proved

codons are 3 nuclotides

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proflavin molecules cause

single base insertions or deletions (frameshift mutation)

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In vitro Translation System

cellular extracts that upon addition of mRNA
can lead to polypeptide synthesis in a test tube

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Marshall Nirenberg and Heinrich Matthaei

In 1961, added a synthetic poly-U (5’…
UUUUUUUUUU…3’) mRNA to cell-free
translational system derived from E.coli.

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deciphering the genetic code

Nirenberg, Khorana and Holley

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In 1965, Nirenberg and Philip Leder

added short synthetic mRNA ONLY 3
nucleotides in length to an in vitro translational
system containing tRNA attached to amino acids,
where only 1 of the 20 amino acids was
radioactive

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Nirenberg and Philip Leder

Codon-amino acid correspondences

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“STOP” codons

UGA, UAA and UAG

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Sydney Brenner

indentified stop codons

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Sydney Brenner used

Point mutations in T4 phage head protein “m”, encoding a component of phage head capsule

nonsense mutation

changes a codon that signifies an amino acid (a sense codon) into one that does not (STOP CODON)

5’ to 3’ in mRNA corresponds to

N to C-terminus in the polypeptide

Proteins are encoded by

non-overlapping triplets of nucleotides called codons in a given gene

initiation codon, AUG

codes for methionine at the start of the reading frame

The genetic code is

degenerate

The three stages of transcription

1. Initiation 2. Elongation 3. Termination

Transcription is carried out by

RNA polymerases

Initation

DNA sequences at the beginning of genes called "promoters" direct the exact location for the initation of transcription by RNA polymerase

What is required for initiation

sigma factor

Core enzyme + sigma =

holoenzyme (RNA polymerase)

sigma factor

reduces RNA polymerase's general affinity for DNA but increases the enzyes affinity for the promoter (binds tighty) and forms closed promoter complex

Open promoter complex

RNA polyerase and unwound promoter

Elongation

Constructing an RNA copy of the gene RNA poly slides along the DNA to synthesize RNA

Elongation rate

50 nucleotides per sec

Once an RNA poly moves way from promoter

a second RNA poly can bind the promoter and initiate transcription

A can express different genes at

different rates

Termination

a terminator is reached that RNA poly and RNA transcipt to dissociate from DNA

Intrinsic terminators

cause RNA poly to terminate transciption on its own

Extrinsic terminators

require addition proteins (*Rho protein*)

Transciption has many

initiator sites

Transcription uses ___ for energy

NTPs

Only small portion of DNA is

transcipted

AIDS uses

reverse transciption

eukaryotic RNA poly II

transcribes genes that encode proteins

reverse transcription

reverse transciptase synthesizes DNAstrands complementary to an RNA template

reverse transcription product

cDNA

RNA processing

in eukaryotes, converts RNA into mRNA

Modification for mRNA

splicing exons (removing introns), and addition of a poly-A tail to the 3' end and a methylated cap at the 5' end

Methylated cap

crucial for efficient translation of mRNA to protein

poly-A tail

consisting of 100-200 A resiues, that stabilizes the mRNA and increases the efficiency of translation initiation

Eukaryotes use ___ that bind to protein factors aiding transciption

enhancer

basal transcription

core promoter by itself produces low level of transcription

Regulatory elements

affect the binding of RNA poly to the promoter 1. Enhancer: stim. transcription 2. Silencers: Inhibit transciption

RNA poly I

rRNA

RNA poly III

tRNA

Methy transferases

add methy (-CH3) groups to backward G m7G meth cap

Poly-A tail length

100-200 As long

Translation initiation factors bind to

methylated cap, while poly-A binding proteins associate with the 3’ poly-A tail

Enhances translation

initiation

DNA nucleotide seq of many eukaryotic genes are much longer than corresponding mRNA

we remove introns

human gene DMD

encodes the protein Dystrophin and mutation can cause Duchenne Muscular Dystrophy

Exons (for expressed regions):

Sequences found in both a gene’s DNA and mature mRNA

RNA Splicing:

The process that deletes introns and joins together successive exons to form mature RNA

Splicing requires a complicated intranuclear machine

Spliceosome

Spliceosome consists of four subunits called

Small nuclear ribonucleoproteins OR snRNPS

Each snRNP contains

1 or 2 small nuclear RNAs (snRNAs

snRNP

-100-300 nucleotides long associated with proteins in discrete particle.

Splicing is catalyzed by

splicesome

Ribozymes

RNA molecules that can act as enzymes to catalyze specific reactions (splice themselves) have 5 snRNAs

alternative splicing

production of different mature mRNAs from the same primary RNA by joining different combinations of exons

Alternative splicing largely explains how

28,000 genes in the human genome can encode hundred of thousands different proteins

Alternative splicing can regulate

localization of proteins and their enzymatic properties.

isoforms

Proteins resulting from alternative splicing

Introns allow for

alternative splicing

Introns can generate

non-coding RNAs (ncRNA) that influence gene expression

snRNA

components of slocesome which is required for RNA splicing

9.1-9.2 Flashcards

(81 cards)