Dna Translation - Genetics

Front 1

Describe a codon.

Back 1

Blocks of 3 bases;

Each codon codes for a different amino acid.

64 possible codon combinations.

Front 2

Describe Polynucleotide Phosphorylase.

Back 2

Enzyme used to synthesise random RNA polymers from nucleotides.

Front 3

How can different Base ratios determine which codons code for each amino acid?

Back 3

The most common amino formed must be associated with most common codon - E.g. Solution with 80/20 of U/G:

Phenylalanine most common amino acid, UUU most common codon therefore associated.

Next most common codons will include x2 U (UGU, UUG, GUU), therefore next 3 most common codons associated.

etc.

Front 4

What are Stop-codons?

Back 4

UAA, UGA, UAG - Indicate when translation should stop.

Front 5

Describe the genetic code.

Back 5

Universal: Same genetic code used across all eukaryotes/bacteria.

Degenerate: Multiple codons can code for same amino acid (except Trp & Met)
Non-overlapping: One codon codes for 1 amino acid, no gaps.

Front 6

What codon do all coding sequences start with?

Back 6

AUG; Codes for Methionine

Front 7

How many possible reading frames are there in an RNA sequence?

Back 7

3; Only one codes the real protein sequence.

Front 8

Describe frameshift.

Back 8

Inserting/deleting a base causes codon reading to move over 1 space, resulting in completely different amino acid sequences being made.

Front 9

Describe tRNA function.

Back 9

Adaptor Molecules;

Recognise at least one codon for a single amino acid.

Carry amino acids; act as translation intermediates.

Amino acids do not recognise own codon that codes for them.

Front 10

Describe tRNA structure. Draw it.

Back 10

Amino acid at 3' end;

Internal base pairings, forming clover leaf structure.

4 loops: DHU (left), Anticodon (bottom), TψC (right), Variable (inbetween TψC/Anticodon)

3'-5' Anticodon (mRNA has 5'-3' codon)

Front 11

What conformation does tRNA acquire?

Back 11

Clover leaf structure folds to form L-shaped molecule.

2 helical regions + bend.

Constant loops TψC / DHU form bend.

Anticodon loop at one end of L, amino acid at other end.

Front 12

What is the function of Aminoacyl-tRNA synthetase?

Back 12

'Charges' tRNA by adding it's corresponding Amino acid;

Has specific binding sites for tRNA and another Amino Acid.

Front 13

What drives the synthesis of charged tRNA?

Back 13

ATP > AMP + PPi

PPi > 2Pi

Breakdown of PPi drives reaction.

Front 14

Why is there an untranslated 5' & 3' region after translation?

Back 14

Region in mRNA at start/end that does not code for Protein.

Does NOT start with AUG and end with UAG.

Front 15

What is the function of Ribosomes?

Back 15

Bring together charged tRNA and mRNA to synthesise a polypeptide by matching codons/anticodons.

Polypeptide synthesised starting from N-terminal.

Front 16

Describe Prokaryotic Ribosome Structure.

Back 16

70s Ribosome: Made from 50s + 30s subunits

50s subunit: Made from 23s + 5s + 31 proteins

30s subunit: Made from 16s + 21 proteins

Front 17

Describe Eukaryotic Ribosome Structure.

Back 17

80s Ribosome: Made from 60s + 40s subunits

60s subunit: 28s + 5.8s + 5s + 49 proteins

40s subunit: 18s + 33 proteins

Front 18

Describe the 3 binding sites of tRNAs.

Back 18

Amioacyl Site (A): Accepts incoming tRNA. Ensures anticodon paired with codon on mRNA.

Peptidyl Site (P): tRNA here pass growing peptide chain to tRNA in A-site. Prepare to leave.

Exit Site (E): tRNA leaves here, makes room for incoming charge tRNA.

tRNA shift across Ribosome sites as new tRNA are added.

Front 19

Describe initiation of translation for Prokaryotes.

Back 19

Sequence on mRNA upstream from start codon AUG tells Ribosome where to start translation - Shine-Dalgarno.

30s subunit binds;

Charged tRNA, mRNA, initiation factors, 30s form complex, requires GTP;

50s encloses tRNA;

70s ribosome forms.

1st tRNA positioned in P-site, not A-site.

Front 20

Describe initiation of translation for Eukaryotes.

Back 20

40s Ribosome bind directly to 5'-cap;

Finds AUG start codon.

40s, mRNA, charged tRNA, initiation factors form complex, requires GTP & ATP.

60s encloses tRNA;

80s ribosome forms.

Front 21

Describe Translation Elongation.

Back 21

(See Elongation Flashcards)

Front 22

Describe how Transcription and Translation interact in Bacteria.

Back 22

Coupled in time and space;

Translation occurs as the mRNA is still being transcribed.

Multiple Ribosomes work on mRNA simultaneously.

Amplication occurs:

Single DNA > Multiple RNAP > Multiple Ribosomes > Multiple Polypeptides.

Front 23

Describe how Transcription and Translation interact in Eukaryotes.

Back 23

Separated in Time and Space;

Transcribed/spliced in Nucleus;

Must finish before mRNA exported into cytoplasm.

Ribosomes bind to mRNA in cytoplasm, Translation occurs.

Front 24

How do amino acids interact with reading codons during translation?

Back 24

Play no role. Only anti-codon on same tRNA determines amino acid incorporation.

Front 25

Explain the Raney Nickel Experiment.

Back 25

Determined Amino acids play no role in reading a codon during translation.

tRNAcys charged with cysteine.

Cysteine treated with Raney Nickel, forming Alanine.

Forms Alanyl-tRNAcys.

tRNA tested with poly(cys-val)/poly(arg-ala). Only paired with (cys-val), despite Alanine bound.

Front 26

Describe the Wobble Hypothesis.

Back 26

Some tRNAs can recognise multiple codons.

Suggests codons recognised by anticodon vary at 3rd base position.

3rd base flexible - can recognise multiple bases.

Front 27

Which bases in the 3rd position of a codon can each base in the anticodon recognise?

Back 27

A: U

C: G

U: A, G

G: C, U

I: U, C, A

Front 28

Which codons can the anticodon 5'-GCU-3' recognise? (remember wobble bases)

Back 28

(Make sure anticodon read 3'-XXX-5' direction)

5'-AGC-3' & 5'-AGU'3'

Front 29

What can a mutation in the gene elF2B cause?

Back 29

Neurodegenerative Disorder; Vanishing white matter.