Protein Synthesis

Question 1

Steps of DNA Transcription

Answer 1

1) RNA Poly separates strands
2) RNA P pairs up free nucleotides to the DNA of template strands by H-bonds.
3) RNA P links nucleus together by covalent bonds between sugars and phosphates.
4) RNA Strand seperates.
5) DNA rewinds

Question 2

Role of H-bonding in transcription

Answer 2

• Can easily be broken to separate RNA strand.

Question 3

How do cells specialize?

Answer 3

They transcribe only the genes that code for specific polypeptides, showing characteristics.

Question 4

Translation

Answer 4

The synthesis of a polypeptide by tRNA that is complementary to codons that code for specific amino acids in ribosomes.

Question 5

Overview of roles in translation:

Answer 5

1) mRNA binds to small subunit, contains codons which code for 1 AC.
2) 2 tRNA attach to large subunit, contains anticodon with corresponding AC.
3) Aminoacids in tRNA are bonded by peptide linkage.

Question 6

The genetic code properties:

Answer 6

• A codon has 3 bases, creating a greater number of different codons, enough for 20 amino acids.
• Degenerate: one AC can be coded for more than 1 codon.
• Universality: all 64 codons have the same meaning in cells of all organisms.

Question 6

Outline the steps in translation:

Answer 6

1) tRNA binds to a site, p site has chain made so far and e site is vacant.
2)Bond is made between a site amino acid and p site amino acid catalysed by ribosomal RNA&raquo_space; Polypeptide is transferred to a site.
3) Ribosome moves 3 bases towards 3’ end, p tRNA moves towards e site, a to p site, a site vacant.
4) t site tRNA detaches and exits, next tRNA at a site binds.

Question 7

How many codons indicate when the translation should end:

Answer 7

three stop codons

Question 8

What is the start codon and for what amino acid does it code?

Answer 8

methionine , AUG

Question 9

Mutation

Answer 9

Change in base sequence of DNA

Question 10

what gene codes for the beta polypeptide of haemoglobin?

Answer 10

HBB

Question 11

Explain the genetic cause of sickle cell disease:

Answer 11

• sixth amino acid changes adenine to thymine (CAC > CTC), transcribes mRNA to GUG codon instead of GAG, a tRNA with the anticodon CAC for valine binds, hemoglobin with valine (hydrophobic) creates sickle cells.

Question 12

In what direction does transcription occur?

Answer 12

5 to 3

Question 13

In what direction does translation occur

Answer 13

5 to 3 bardo

Question 14

promotor

Answer 14

section of DNA that is a promotor where RNA Polymerase binds, start of a gene.

Question 15

What do repressor proteins do?

Answer 15

Bind to promotor and prevent transcription.

Question 16

Transcription Factors

Answer 16

Proteins that bind to promoter sites to promote or prevent RNA P from binding and inhibit transcription.

Question 17

Outline the roles of non-coding DNA:

Answer 17

• Regulating gene expression: promoters or protein binding sites promote/repress, which is important for transcription.
• introns; roles in mRNA processing
• telomeres: prevents parts of important genes from being lost during replication.
• transcribing these genes produces tRNA for translation and ribosomal RNA.

Question 18

What are the two types of post-transcriptional modification:

Answer 18

adding extra at the ends of transcript nucleotides or removal of nucleotides

Question 19

4 types of modification

Answer 19

• five prime cap; contains three Ps, guanine and an extra methyl group, stabilizes mRNA, prevents digestion by nuclease enzymes.
• poly A tail, makes translation stop.
• introns are removed, remaining exons are spliced together.

Question 20

How is translation started?

Answer 20

1) tRNA with anticodon AUG binds.
2) small subunit and initiator tRNA attach to 5’ and move along the mRNA until they reach the start codon.
3) tRNA anticodon and codon pair up.
4) A large subunit binds to a small unit.
5) tRNA binds to A site.
6) A peptide bond is formed between the amino acids.

Question 21

A, P, E site stand for

Answer 21

amino acyl, peptidyl, exit

Question 22

What are the main types of protein modification?

Answer 22

• changes to side chains of amino acids.
• folding into tertiary stricture.
• excising part of the polypeptide.
• combining polypeptides to form Q protein.

Question 23

how is preproinsulin (110 AC) modified into insulin?

Answer 23

• protease in the rER lumen removed 24 AC sequences from the N-terminal&raquo_space; proinsulin
• folded, 3 S-S bonds are created to stabilize the tertiary structure.
• proteases in Golgi remove 33 AC seq by breaking peptide bonds between lysine and arginine at 2 positions.
• 2 AC are removed from the C-terminal of the B chain, to create insulin with 51 AA.

Question 24

Proteasomes

Answer 24

organelles that digest specific proteins

Question 25

how do proteasomes digest proteins

Answer 25

• they recognize proteins marked by ubiquitin at either end.
• polypeptide is folded and fed into central chamber.
• active sites of proteasomes digest it into amino acids.