DNA (+ replication)

Question 1

name 2 polynucleotides

Answer 1

DNA
RNA

Question 2

describe the structure of DNA

Answer 2

DNA is a polynucleotide that is made up of many nucleotide monomers
a nucleotide consists of a phosphate group bonded to a deoxyribose sugar (pentose) and a base (adenine, thymine, guanine, cytosine)
the nucleotides undergo a condensation reaction so they can form phosphodiester bonds
DNA has a double-helix structure

Question 3

describe how a phosphodiester bond is formed between 2 nucleotides within a molecule

Answer 3

2 nucleotides undergo a condensation reaction which is catalysed by DNA polymerase and a phosphodiester bond forms between the phosphate group of 1 nucleotide and the sugar of another

Question 4

why is having a sugar-phosphate backbone an advantage for DNA

Answer 4

it protects more chemically reactive bases that are inside of the double helix

Question 5

why is having a double helix an advantage for DNA

Answer 5

increases the stability of the molecule

tightly coils to store a lot of information in a small space

Question 6

name 2 nucleic acids

Answer 6

DNA
RNA

Question 7

what is the function of DNA

Answer 7

carry/store genetic information

Question 8

what does DNA stand for

Answer 8

Deoxyribonucleic acid

Question 9

how is hereditary information passed on

Answer 9

from cell to cell (mitosis)
passed on from generation to generation

Question 10

what does RNA stand for

Answer 10

Ribonucleic acid

Question 11

what is the function of RNA

Answer 11

transfers genetic information from DNA in the nucleus to ribosomes in the cytoplasm

Question 12

why does A always have to be paired with T

Answer 12

they are complimentary base pairs therefore hydrogen bonds can form between them

Question 13

how many hydrogen bonds form between A and T

Answer 13

2 hydrogen bonds

Question 14

how many hydrogen bonds form between C and G

Answer 14

3 hydrogen bonds

Question 15

how do you describe that 2 polynucleotide strands run in opposite directions

Answer 15

anti parallel

Question 16

what is an advantage of hydrogen bonds

Answer 16

they make DNA stable especially in areas of high G - C pairings

Question 17

if there are equal percentages of A + T what type of cell are you looking at

Answer 17

human body cell
(it is double-stranded due to same percentages)

Question 18

what is the name of the sugar in RNA

Answer 18

ribose sugar

Question 19

name the bases of RNA

Answer 19

Adenine (A)
Guanine (G)
Cytosine (C)
Uracil (U)

Question 20

what are the 3 types of RNA and what are their functions

Answer 20

mRNA - made in transcription
tRNA -role in translation as it carries the amino acid to the ribosome
rRNA - proteins that make up ribosomes

Question 21

list all of the similatires between DNA and RNA

Answer 21

both have the bases of cytosine, adenine, guanine
both have a phosphate group
both have a phosphate sugar backbone
both have phosphodiester bonds

Question 22

list 2 difference of RNA compared to DNA

Answer 22

RNA
- much shorter
- single-stranded

DNA
- 2 strands are anti-parallel
- double helix
- lots of hydrogen bonds

Question 23

how is DNA adapted for it’s function (6 marks)

Answer 23

stable

• many hydrogen bonds between bases and these are protected by sugar-phosphate backbone
• can pass information between generations without changing

A binds to T
G binds to C

• protects the genetic code from being changed by chemical/physical forces
• allows for successful DNA replication and transcription

very large
- carries a lot of information
(double helix makes DNA compact)

hydrogen bonds between bases are individually weak
- strands are easily separated during DNA replication and transcription

Question 24

describe the process of semi conservative DNA replication

Answer 24

• DNA helicase breaks the hydrogen bonds which separates the strands
• both strands act as templates
• free nucleotides attach to the template strands on their complimentary base (A T C G)
• DNA polymerase joins nucleotides together in a new strand
  hydrogen bonds form between the complementary base pairs

semi conservative DNA replication is when a new DNA molecule contains 1 new and 1 original strand

Question 25

why does DNA replication go from the 3 prime to the 5 prime direction

Answer 25

DNA polymerase has an active sit that is only complementary to the 3 prime end of the new DNA strand so DNA polymerase can only add nucleotides to the 3 prime end of a new DNA strand

Question 26

what did the meselson and stahl experiment prove

Answer 26

that dna replication is semi conservative

Question 27

what 2 isotopes of nitrogen was used in meselson and stahls experiment

Answer 27

15N
14N