2.7 DNA replication, transcription and translation

Question 1

DNA replication according to the semiconservative model

Answer 1

dna replication is SEMI-CONSERVATIVE mmhm yup

after replication, each new DNA strand consists of:
- 1 strand of DNA from og template molecule
- 1 strand of newly synthesized DNA

Question 2

three hypotheses proposed for method of DNA replication

Answer 2

• conservative model
  entirely new molecule syn from DNA template
• semi-conservative model
  one new strand, one template strand
• dispersive model
  segments of new and old DNA

Question 3

what did the Meselson-Stahl experiment confirm?

Answer 3

the theory that DNA replication was semi-conservative

Question 4

how did the meselson and stahl experiement yield its results 4

Answer 4

1. used radioactive isotopes of nitrogen – heavier 15N and lighter 14N
2. DNA molc prepared using 15N and replicated in presence of 14N
3. after 1 division: mix of 15N and 14N – disproved conservative model
4. after 2: some DNA solely 14N – disproved dispersive model

Question 5

what are the 2 enzymes that coordinate DNA replication

Answer 5

helicase and DNA polymerase

Question 6

what role does helicase play in DNA replication

Answer 6

• unwinds double helix, seperates the 2 polynucleotide strands
• breaks hydrogen bonds between complementary base pairs
• the 2 sep strands will act as templates

Question 7

what role does DNA polymerase play in DNA replication

Answer 7

• synthesizes new strands from the 2 parental template strands

free deoxynucleoSIDE triphosphates (nucleotides with 3 phosphate grps) align opposite their complementary base partner

• cleaves the 2 excess phosphates – uses energy released to link the nucleotide to the new strand

Question 8

what is PCR and what is it used for

Answer 8

Polymerase chain reaction
- artifical method of replicating DNA
- used to amplify large quantities of a specific sequence from a small sample
- each reaction doubles amt of DNA

Question 9

3 steps to PCR

Answer 9

1. denaturation – DNA sample heated to sep strands
2. annealing – sample cooled to allow primers to anneal (at start and end)
3. elongation – sample heated to optimal temp for heat-tolerant polymerase (Taq) (extends chain)

Question 10

what is Taq DNA polymerase and what does it do

Answer 10

• an enzyme isolated from bacterium Thermus aquaticus
• optimal temp of 75C – can function at high temps used in PCR w/o denaturing
• it EXTENDS the nucleotide chain from the primers

Question 11

what is transcription?

Answer 11

• process by which an mRNA sequence is produced from a DNA template copied by RNA polymerase
• RNA polymerase seperates DNA strands, synthesizes a complementary RNA copy

Question 12

where does transcription occur

Answer 12

the nucleus (where DNA is)
- rna then moves to cytoplasm for translation

Question 13

what is the strand that is transcribed called

Answer 13

the antisense strand
- complementary to the RNA sequence

Question 14

what is the strand that is NOT transcribed called

Answer 14

sense strand
- identical to RNA sequence (with T instead of U)

Question 15

4 steps of transcription

Answer 15

1. RNA polymerase seperates the DNA strands
2. RIBONUCLEOSIDE TRIPHOSPHATES align oppose their exposed complementary base partner
3. RNA polymerase removes additional phosphate grps – uses the energy released to covalently join the nucleotide to the sequence
4. once it has been synthesized, RNA polymerase detaches from DNA and double helix reforms

Question 16

what direction does transcription occur

Answer 16

5’ –> 3’

Question 17

what is translation?

Answer 17

• process of protein synthesis – genetic info encoded in mRNA is translated into AA sequence on polypeptide chain

Question 18

where does translation occur

Answer 18

the cytoplasm

Question 19

6 steps of translation

Answer 19

1. ribosomes bind to mRNA, move in a 5’–>3’ direction until start codon AUG
2. anticodons on tRNA align opp codons according to complementary base pairing
3. each tRNA molecule carries a specific amino acid
4. ribosomes catalyse formation of peptide bonds (betw adjacent AAs)
5. ribosome moves along mRNA synthesizing a polypeptide chain until stop codon
6. translation ceases at stop codon, polypeptide chain released

Question 20

stop codons

Answer 20

UAA
UGA
UAG

Question 21

what are codons and what do they do?

Answer 21

• base sequence of mRNA read by ribosome in triplets of bases – codons
• each codon codes for 1 AA with a polypeptide chain
• order of codons in mRNA determines order of AA

Question 22

coding region of an mRNA sequence

Answer 22

begins with start codon
ends with stop codon

Question 23

features of genetic code

Answer 23

• universal
• triplet code
• degenerate (more than one codon can code for the same AA)
• punctuated (start and stop codons)
• non overlapping (Each nucleotide is only read once)

Question 24

what makes production of human insulin in bacteria possible

Answer 24

• genetic code is universal
• same codons code for same AA – genetic info transferrable

Question 25

production of human insulin in bacteria

Answer 25

1. insulin prod gene extracted and cut using restriction enzyme
2. same restriction enzyme cuts bacterial plasmid – complementary sticky ends
3. stuck tgt with DNA ligase
4. recombinant plasmid inserted into transgenic bacteria w heat shock
5. transgenic bacteria selected and cultured in fermentation tank