(7) Nucleic Acids

Question 1

Describe the initiation of transcription, including the role of the promoter, transcription factors and RNA polymerase

Answer 1

Transcription is the proccess by which a DNA sequence (gene) is copied into a complementary RNA sequence by RNA polymerase. The promoter (a short sequence of base pairs that are not transcribed) located on the antisense binds with mRNA and tells it to begin transcription

Question 2

Describe the elongation of transcription, including the role of the nucleotide, triphosphates and the direction of transcription

Answer 2

Transcription is the process by which a DNA sequence (gene) is copied into a complementary RNA sequence by RNA polymerase. Free nucleotides exists in the cells as nucleotide triphosphates (NTPs) which line up opposite their complementary partner.

Question 3

describe termination of tranoscription including the role of the terminator

Answer 3

RNA polymerase transouilres until told to stop. The terminator is a sequence of DNA that acts as this signal

Question 4

list two major differences in gene expression between prokaryotic and eukaryotic cells

Answer 4

A) Pro: control of gene expression taken place during transcription

EUK: intracellular organelles add to complexity

B) PRO: transcription + translation occur simultaneously in cytoplasm
EUK: transcription in nucleus

Question 5

state the effect of DNA methylation on gene expression

Answer 5

DNA methylation regulates gene expression by recruiting protein involved in gene expression or by initiating the trending of transcription factors to DNA. IT essentially blocks the promoter site.

Question 6

Outline the effect of methylation on nucleosome tails of gene expression

Answer 6

chemical modification of tritone tails can either activate/deativate or increase/decrease gene expression

Question 7

outline two examples of environmental influence on gene expression

Answer 7

• drugs and chemicals
• temperature and light

Question 8

outline gene expression

Answer 8

the processes by which information from a gene to synthesize a functional gene product that enables it to produce non-coding RNA

Question 9

Outline the process of translation initiation.

Answer 9

1. The small subunit of the ribosome binds to the 5’ end of the mRNA
2. The anticodon of the initiator tRNA binds to the start of the codon on the mRNA by hydrogen bonds

Question 10

Outline the process of translation elongation

Answer 10

1. charged tRNA binds to the A site
2. to bind, the anticodon of the tRNA must be complimentary to the codon of the mRNA by hydrogen bonds
3. a peptide bond forms between the amino acids at the P and A sites
4. the tRNA at the P site detaches from the amino acid
5. the ribosome moves one codon along the mRNA (5’-3’)
6. The tRNA with the growing polypeptide chain is now in the P site
7. the tRNA with no amino acid is now in the E site and exits the ribosome
8. a newly changed tRNA can now enter the A site

Question 11

State the direction of movement of the ribosome along the mRNA molecule

Answer 11

5’ → 3’ direction

Question 12

Outline the process of translation termination

Answer 12

1. The ribosome moves down the mRNA until the stop codon is in the A site, tRNA can’t bond to the stop codons
2. Proteins called release factors bind to the A site
3. This causes the polypeptide chain to be released from the tRNA in the P site. The ribosome separates from the mRNA and splits into subnuits

Question 13

State the difference between free and bound ribosomes

Answer 13

free= synthesize proteins for use primarily within the cell

bound= synthesize proteins primarily for secretion or use in lysosomes

Question 14

list destinations of proteins synthesized on free ribosomes

Answer 14

cytoplasm, mitochondria, chloroplasts

Question 15

compare the timing and location of transcription and translation between prokaryotes and eukaryotes

Answer 15

once transcription is complete in euk, the transcript is modified in several ways before exiting the nucleus. thus, there is a delay between transcription and translation. in pro, as soon as the mRNA is transcribed, translation begins

Question 16

describe the primary structure of a protein

Answer 16

the number and sequence of amino acids that make up the linear polypeptide. the number and sequence is determined by the base sequence of the gene. the primary structure will determine how the polypeptide will fold up following translation. shape of protein determines function.

Question 17

describe the secondary structure of a protien

Answer 17

secondary strucutre represents the first level of protein folding. hydrogen bonds form between polar C-O and N-H groups within the polypeptide backbone. these groups are positioned on either side of each peptide bond.

there are 2 types of folding that can contribute to secondary structure:
a) alpha helix- polypeptide forms a helic with hydrogen bonds between the turns of the helix
b) beta plated sheets- sections of the polypeptide align parallel to each other, hydrogen bond form between them.

In both, a and b, hydrogen bonds stabilize structure

Question 18

describe the tertiary structure of protien

Answer 18

tertiary structure = final shape

R groups determine the way the polypeptide chain folds up. there are 4 types of interactions between R groups that hold the structure

a) hydrogen bonds form between amino acids with polar R groups

b) ionic bonds form between amino acids with the oppositely charged R groups

c) disulfide bridges form between 2 amino acids containing sulfur in the R group

d) hydrophilic interactions form between amino acids with non polar R groups

Question 19

outline the quaternary structure of a protien

Answer 19

some protiens are comprised of more then one polypeptide. intermolecular bonds gold different polypeptide chains together. the number and position of the polypeptide chain is called the quaternary structure

Question 20

outline the process of attaching an amino acid to the tRNA by the tRNA activating enzyme

Answer 20

1. ATP is hydrolosized and the amino acids is covalently linked to the AMP
2. the amino acid is covalently linked to the tRNA and AMP is released
3. charged tRNA is released from the active site

Question 21

describe the structure of ribosomes

Answer 21

ribosomes = rRNA & protiens

2 subunits: small (rRNA binding site)
large (tRNA binding sites with A,P,E)

Question 22

outline the structure of tRNA molecules

Answer 22

the tRNA molecule has a distinctive folded structure with 3 hairpin loops that form the shape of a 3 leaf clover

Question 23

outline the structure of a polysome

Answer 23

a single mRNA and several attaches ribosome. 1 ribosome per abt 100 nucleotides

Question 24

what is the difference between a peptide, polypeptide and a protein

Answer 24

peptide: 2+ amino acids joined by peptide bonds
polypeptide: chain of amino acids
protein: contains 1+ polypeptide