Lec 10: Protein Synthesis Flashcards Preview

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Flashcards in Lec 10: Protein Synthesis Deck (34)
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1
Q

what is the purpose of transcription? why does it occur in the nucleus?

A

Transcription is the process by which DNA is copied (transcribed) to mRNA, which carries the information needed for protein synthesis

it occurs in the nucleus because this is where the DNA is located

2
Q

what is the template strand? state the other name given to this polymer

A

single strand of mRNA

antisense strand/non conding strand

3
Q

what is the cap for Pre-mRNa composed of?

A

phosphorylated 7 ‐methyl guanosine

4
Q

what adds the cap to pre-mRNA. where is the cap place on the mRNA molecule?

A

guanyltransferase adds the cap to the 5’ end of the mRNA

5
Q

what is the importance of pre-mRNA capping?

A

– Ensures mRNA is exported out of nucleus

– Blocks degradation of mRNA by 5’ exonucleases

– Promotes translation

6
Q

what is the polyadenylation of Pre-mRNA and why is this important in transcription

A

this is where appr.200 adenosine residues are added to pre-mRNA

So:

  • pre-mRNA is cleaved by an endonuclease near a signal AAUAAA sequence at the 3’ end
  • the adenosine residues are added at the cleavage site by poly‐A polymerase

importance:

  • poly‐A‐tail protects the mRNA from degradation by 3’ exonucleases
  • aids in termination of transcription
  • ensures export from the nucleus
7
Q

what are the difference between exons and introns?

A

*EXtra special & *IN the way

exons code for proteins

introns do not code for proteins so need to be spliced out to produce the final mRNA

8
Q

what is alternative splicing?

A

this is where the pre-mRNA sequence is spliced to produce different proteins from the same gene

9
Q

what is mature mRNA

A

mRNA that has been spliced and processed

and is ready for translation

10
Q

what does mature mRNA consists of?

A

Mature mRNA consists of:

  • 5’ cap
  • 5’ UTR (untranslated region)
  • Coding Region (to be translated into a protein)
  • 3’ UTR (untranslated region)
  • Poly(A) tail
11
Q

what is the name given to 3 bases e.g ACG

A

DNA base triplet

12
Q

what is the name given to base triplets in mRNA

A

codons

13
Q

how many mRNA codons are there?

A

64 (43)

14
Q

what is meant by degenerate with respect to the genetic code?

A

More than one codon codes for each of the 20 amino acids

15
Q

why are the first two codons most crucial?

A

gives tolerance against mutation

16
Q

state the bases that code for the START and STOP codons

A

– START codon: AUG (methionine)

– STOP codons: UAG, UAA, UGA

17
Q

how does a mutation in the amino acid sequence affect haemoglobin?

A

change in amino acid sequence causes haemoglobin to crystallise when oxygen levels are low, causing the sickle shape which gets stuck in small blood vessels

18
Q

what is the consequence of sickle cell anemia in terms of red blood cell function?

A

compared to normal red blood cells, sickle red blood cells can not move as easily through the blood stream

resulting in;

– Downstream tissue ischaemia, causing pain and infarction

– In severe cases, organ damage and ischaemic stroke

19
Q

in sub-saharan africa what does sickle cell anemia provide protection against

A

malarial parasite

20
Q

what is meant by frameshift mutation?

A

small deletions or insertions into a DNA sequence can resulting in significant changes of protein sequence

21
Q

what is translation? where does it occur?

A

genetic code carried by mRNA is decoded to produce the specific sequence of amino acids in a polypeptide chain

in the ribosome

22
Q

what is a ribosome composed up of?

A

60S subunit and smaller 40S subunit

23
Q

what name is given to the triplet bases complementary to the codon on a mRNA molecule

A

anticodon

24
Q

what is a aminoacyl tRNA molecule?

A

a tRNA molecule bonded to an amino acid

25
Q

what is a deacylated or uncharged tRNA molecule?

A

tRNA molecule that has had its amino acid removed

26
Q

what is a peptidyl tRNA?

A

a tRNA molecule bound to a growing polypeptide chain

27
Q

what is initiation?

A

binding of ribosome to 5’ end of mRNA and hydrogen binding of the anticodon of an aminoacylated tRNA carrying methionine on the AUG start codon

28
Q

what is elongation?

A

the addition of further amino acids to the growing polypeptide chain brought by corresponding aminoacylated tRNAs.

29
Q

what is the function of peptidyl transferase?

A

creates covalent peptide bonds between amino acids

30
Q

what is termination?

A

when the stop codon (UAG, UAA, UGA) is reached and the peptide and ribosomal subunits are released

31
Q

where do proteins synthesised on free ribosomes end up?

A

cytoplasm

32
Q

where do proteins synthesised on ribosomes attached to RER end up?

A

secreted our of the cell

33
Q

how are proteins secreted?

A

proteins are incoporated into vesicles

for transport to the golgi apparatus

post translational modification of proteins occurs in the goldi cavaties e.g glycosylation

modified proteins traverses the GA and is packaged into secretory vesicles

these vesicles move to the cell membrane, fuse with it and expel their contents into the extracellular space (excytosis)

34
Q
A