D1.2 - transcription and translation

Do A and U have 2 or 3 hydrogen bonds

2

How many H bonds to C and G have

3

gyrase

helps to support DNA when it is unwound

why is gyrase important in cells such as neurons that never undergo mitosis?

the DNA is never recreated so must remain intact for the life of the cell

histones

proteins that form structural units (nucleosomes) that help support the structure for the life of the organism

what genes are bound tighter to the histones?

genes that are never/rarely expressed

how can cells increase the rate of transcription

altering the binding of DNA and histones to make it easier/faster for RNA polymerase to move along the strand

do coding mutations have an impact on protein synthesis

Yes

how does the cell regulate gene expression

by blocking start codons so that RNA polymerase cannot bind, so the gene is switched off and never expressed or transcribed

promoter region

binding site at the start of the gene

Large ribosome subunit

Binds simultaneously to the mRNA binding to the small ribosomal subunit and contains active sites for the formation of the new protein

Small ribosomal subunit

mRNA binds to this

What end of the tRNA molecule is the amino acid binding site?

3’

What is at the bottom of the tRNA molecule

Anticodon to the codon undergoing translation on the mRNA

3 stop codons

UAA, UAG, UGA

How many amino acids are there

20

How many possible triplet codes are there

64

Degenerate code

Several codons can code for the same amino acid

Start codon

AUG - methionine

Universality

All organisms use the same bases and most use the same set of degenerate code

Base substitution in sickle cell anemia

GAG to GTG

What direction is mRNA formed in translation

5’ to 3’ - free nucleotides are added to the 3’ end

Direction of transcription

5’ to 3’ - only the 5’ end of mRNA can bind to the small subunit

Sense strand

The strand that is not being copied - RNA polymerase binds to it

Antisense strand

The strand that is copied in transcription

Activators

Transcription factors that bind to the promotor region to enable binding of RNA polymerase.

Enhancers

Can bind to speed up the rate of transcription

Repressors

Transcription factors that bind and block the promotor region.

Gene silencers

Can slow down rate of transcription or interfere with mRNA

What transcription factors must be present for transcription to occur

2 activators and no repressors.

types of non coding DNA (4)

gene promoter regions, telomeres, introns and locations for tRNA and rRNA

telomeres

section on non coding DNA at the ends of chromosomes - do not code for anything - act as protection

introns

sections between exons - not expressed

exons

coding DNA - expressed - produce a protein

Post transcriptional modifications (3)

Guanine added to 5’ end, poly A tail (multiple Adenines) added to 3’ end, splicing

poly A tail function

increase mRNA stability, helps transport molecule to ribosome

Guanine on 5’ end post modification function

stabilises mRNA and helps it mind to the ribosomes

splicing

removing introns from pre-mRNA, turning it into mature mRNA to leave the nucleus

what are the 3 binding sites in the large ribosomal subunit

E, P, A

when does initiation of translation start

when the 5’ cap binds to the small subunit

what happens after the 5’ cap binds to the small subunit

a tRNA molecule with the anticodon UAC which carries methionine, binds to the start codon (AUG)

what happens in translation once the tRNA binds to the start codon?

the large subunit binds so that methionine is in the P site, tRNA brings in the next amino acids to the A site and they move from A to P to E - where they exit the cell

first stage of translation

Initiation

what bond is formed between the carboxyl group in the P site and the amino acid in the A site

covalent (peptide)

at which site is the amino acid released

E

what direction does the ribosome move along the mRNA

5’ to 3’

translational translocation

mRNA moving through the ribosome

elongation

protein getting longer in translation

why does translation stop at a stop codon

there is no corresponding amino acid

3 stages of transcription

initiation, elongation, termination

antisense strand

copied in transcription

transcriptome

full range of RNA made in a cell

alternative splicing

the same RNA can be spliced in many ways since different exons can be skipped or used, meaning one gene can form multiple variations of protein (protein isoforms)