DNA Replication + Structure

Question 1

what is the replication of DNA and what does it depend on

Answer 1

• replication of DNA is semi conservative

- depends on complementary base pairing

Question 2

-Meselso and stahl

Answer 2

-proved that the semi conservative replication of DNA was correct

Question 3

what is the semiconvesrvative theory of DNA

Answer 3

• mechanism of DNA replication where two new copies of DNA are produced, from an original DNA strand, consisting each of the original strand and a newly synthesized strand

Question 4

how did Meselson and Stahl prove this theory

Answer 4

• by using nitrogen isotopes (extra neutrons) marking a parent DNA that allowed them to show how one old strand and a newly synthesized strand were made up
• use E.Coli bacteria as an example

Question 5

what 3 theoretical ways of DNA replication exist

Answer 5

1. conservative (parental DNA is conserved; two new strands)
2. dispersive (mixture of new and old DNA within the same chromosome)
3. semi conservative (one old and one new strand)

Question 6

enzymes involved in DNA replication

Answer 6

• DNA ligase
• Helicase
• Single-srand binding proteins
• DNA polymerase

Question 7

when does DNA replication happen

Answer 7

during interphase

Question 8

what does DNA ligase do

Answer 8

joins together the short sections on the lagging strand (called the okazaki fragments)

Question 9

what does helicase do

Answer 9

• unwinds the double helix and separates the two strands by breaking the hydrogen bonds

Question 10

what do the single strand binding proteins do

Answer 10

keep the DNA strands separated during replication so that they don’t recoil

Question 11

what does DNA polymerase do

Answer 11

in a 5’-3’ direction it catalyzes the formation of a new polynucleotide chain by linking nucleotides together to form a new trans, using the preexisting strand as a template,

Question 12

STEP 1 of DNA replication

Answer 12

1. helicase undinwds the double helix, breaking the hydrogen bonds between the complementary bases and separating the two strands

Question 13

STEP 2

Answer 13

• each separated strand now is a template for a new strand

- there are man free nucleotides around the replication fork which then bond to the template strands

Question 14

STEP 3

Answer 14

• free nucleotides form hydrogen bonds with their complimentary base pairs on the template strand (Adenine-Thymine, Guanine-Cytosine)
• DNA polymerase is the enzyme responsible for this (works in a 5-3 direction)

LEADING STRAND: (5’-3’)
LAGGING STRAND: (3’-4’): okazaki fragments formed that are joined by DNA ligase

Question 15

Step 4

Answer 15

• new covalent bond are formed, and a NEW dan strand

Question 16

STEP 5

Answer 16

• pairing of complemtanry bases preserves the sequence of bases when DNA replicates
• the new strands formed are completmaty to their template strand but identical to the opposite strand
• DNA replication is semi convservatibe
• new strands and old strand rewied

Question 17

what is the replication fork

Answer 17

• form the DNA takes when it unwinds to open the templates