Protein Synthesis

Question 1

how much of DNA is tanscribed in protein synthesis?

Answer 1

only some of it - a specific gene

Question 2

translation

Answer 2

change from base sequence to amino acid sequence

Question 3

4 differences between transcription and DNA replication

Answer 3

• 1 strand acts as template vs 2
• RNA nucleotides complementary base pair vs. DNA nucleotides
• RNA polymerase vs. DNA polymerase
• only 1 gene transcribed vs. whole molecule

Question 4

exon splicing

Answer 4

1. introns cut out of pre-mRNA using enzymes
2. exons then spliced together

Question 5

% of DNA that is introns

Answer 5

98%

Question 6

why does exon splicing only occcur in eukaryotes?

Answer 6

prokaryotic DNA does not contain introns

Question 7

2 types of post-translational modification

Answer 7

1. removal of Met a.a. if it is not part of the primary structure of the polypeptide
2. polypeptide transported in a vesicle to Golgi for chemical modification (addition of functional group) and packaging into secretory vesicles or lysosomes

Question 8

what do lysozymes do

Answer 8

break down murein in bacterial cell wall

Question 9

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

Answer 9

AUG coding for Met

Question 10

why are 2 tRNA molecules attached to the mRNA at any given time?

Answer 10

so 2 amino acids can be close enough for a peptide bond to form

Question 11

6 steps of transcription

Answer 11

1. DNA helicase unwinds and unzips the DNA doube-helix adn the hydrogen bonds between strands break
2. only 1 strand of DNA - the antisense strand - acts as a template
3. free RNA nucleotides align themselves along the template strand, opposite their complementary DNA bases and H-bonds form between them
4. RNA polymerase moves along the free nucleotides, forming phsophodiester bonds between them and joining them together to form a single RNA polynucleotide
5. at the end of the gene sequence, mRNA is detached and the DNA rewinds into a double-helix. the mRNA now carries complementary codons which will code for secific a.a.
6. mRNA leaves the nucleus through nuclear pores to te cytoplasm where it attaches to ribosomes consisting of rRNA and proteins

Question 12

8 steps of translation

Answer 12

1. mRNA attaches to a ribosome so 2 codons can be read at a time
2. an a.a. in the cytoplasm is activated by ATP and attaches to a specific amino acid at the opposite en to the anticodon
3. tRNA molecules bring specific amino acids to the mRNA at the ribosome
4. the 1st tRNa anticodon complementary base pairs th the start codon on the mRNA and H-bonds form between them
5. another tRNA complementary base pairs with the second codon
6. ribosomal enzymes catalyse the formation of peptide bonds between the first and second amino acids. the 1st tRNA is released into the cytoplasm and binds with the same specific amino acid
7. Ribosome boves along, 1 codon at a time so atRNA can fill the next space
8. each amino acid can then form a peptide bond with the last amino acid of the polypeptide strand
9. when the stop codon is reached, translation stops and the polypeptide is released

Question 13

Function of stop codon in translation

Answer 13

Signals to ribosome it can stop translation and results in the polypeptide detaching from the ribosome