8- Gene expression

Question 1

What 2 things can a gene code for?

Answer 1

1. amino acid sequence of polypeptide

2. functional RNA (e.g. tRNA, rRNA)

Question 2

what is a locus?

Answer 2

fixed position that a gene occupies on a particular DNA molecule

Question 3

main features of genetic code (4)

Answer 3

• universal
• non-overlapping
• degenerate
• non-coding regions (in eukaryotes)

Question 4

2 types of protein synthesis=

Answer 4

• transcription (mRNA produced)

- translation (mRNA converted to protein)

Question 5

where does transcription occur?

Answer 5

nucleus

Question 6

where does translation occur?

Answer 6

cytoplasm, on ribosomes

Question 7

main features of mRNA (3)

Answer 7

• chemically unstable (so breaks down in a few days)
• it acts as a template for translation in the cytoplasm
• straight-chain molecule structure

Question 8

tRNA structure (5)

Answer 8

• single polynucleotide strand,
• folded into 3 loops
• held together by H bonds
• has a specific amino acid
• has an anticodon (complementary to mRNA codon

Question 9

similarities between tRNA and mRNA

Answer 9

they are both polynucleotide strands

Question 10

differences between tRNA and mRNA (3)

Answer 10

• mRNA is a single helix/straight, tRNA folded into clover shape
• mRNA is longer
• mRNA has no paired bases or H bonds, tRNA has some paired bases & H bonds

Question 11

transcription process (5)

Answer 11

1. - DNA double helix unzipped by 
     helicase;
   - H bonds broken
2. - RNA nucleotides align next to 
     complementary bases on the 
     template strand
     - forming (temporary) H bonds
3. - RNA polymerase joins adjacent 
     nucleotides (condensation), 
    - forming phosphodiester bonds
4. when RNA polymerase reaches 
    STOP codon, pre-mRNA 
    detaches from DNA
5. mRNA leaves the nucleus via 
    nuclear pore

Question 12

post- transcription modification

Answer 12

splicing of pre-mRNA > mRNA

This is the removal of introns

Question 13

Translation process (6)

Answer 13

1. mRNA attaches to a ribosome (on RER)
2. tRNA anticodon binds to complementary mRNA codon
3. tRNA brings specific amino acid
4. These AA are joined by peptide bonds using energy from ATP
5. tRNA detaches & the ribosome moves along the mRNA strand to the next codon to form the polypeptide
6. continues until STOP codon