From DNA to Proteins

Question 1

What does the S value of an organelle signify?

Answer 1

High S value = larger mass

S values are not added together.

Question 2

What is mRNA?

Answer 2

• synthesised from DNA template in a long linear transcript
• processed to mature form just outside of nuclear membrane (splicing)
• has 5’CAP and 3’ Poly A tail

Question 3

What are 80s ribosomes formed from?

Answer 3

4 main types of rRNA combined with proteins.

Question 4

Where are ribosomes located?

Answer 4

On membranes of the endoplasmic reticulum

Question 5

What happens if the first amino acids of a peptide are hydrophobic?

Answer 5

Peptide passes through ER membrane to Golgi apparatus.

Question 6

What happens if the first amino acids of a peptide are hydrophilic?

Answer 6

Peptide is dissolved into the cytoplasm.

Question 7

What is the function of tRNA?

Answer 7

• tRNA molecules carry amino acids to ribosomes and check they are incorporated into the right position
• each tRNA molecule carries one amino acid
• anticodon is complementary to triplet on mRNA, which means the right amino acid is added to the polypeptide

Question 8

How is primary mRNA processed into mature mRNA?

Answer 8

Splicing: enzymes remove introns and join exons (specific patterns in DNA sequence shows where to cut)
PolyA tail is added to 3’ end

Question 9

What is meant by degenerate and unambiguous code?

Answer 9

Degenerate: many amino acids are specified by more than one codon
Unambiguous: each codon only specifies one amino acid

Question 10

What is meant by almost universal code?

Answer 10

• all organisms use the same code

- less than 10 exceptions

Question 11

What is meant by non-overlapping code?

Answer 11

Codons do not overlap and each nucleotide is only read once.

Question 12

How is gene expression initiated?

Answer 12

• transcription factors bind to promoter region.
• transcription complex forms around TATA box 5’ of first exon
• transcription commences

Question 13

How is gene expression inhibited?

Answer 13

• repressor proteins inhibit RNA polymerase binding to promoter region
• lack of transcription and processing proteins
• lack of phosphorylation prevents formation of complexes
• inactivated enzymes
• unstable RNA

Question 14

Do mitochondria use the same genetic code as the nucleus of eukaryotic cells?

Answer 14

No, different stop codons.