biological molecules - nucleic acids and DNA

Question 1

what is the structure of a DNA nucleotide

Answer 1

a deoxyribose pentose sugar attached to a phosphate group (PO4 3-) and a nitrogenous base

Question 2

what is the difference between DNA and RNA

Answer 2

DNA = deoxyribonucleic acid
RNA = ribonucleic acid

the pentose sugar in DNA is deoxyribose, in RNA it is ribose

Question 3

what is the monomer unit for nucleic acids

Answer 3

nucleotides

Question 4

what are the 5 nitrogenous bases

Answer 4

A - adenine
C - cytosine
G - guanine
T - thymine (DNA only)
U- uracil (RNA only)

Question 5

what bonds are found in nucleic acids strands

Answer 5

phosphodiester bonds

these form between the phosphate group of carbon 5 and the OH group on carbon 3 of pentose sugar
formed in a condensation reaction
broken by hydrolysis

these form the sugar-phosphate backbone

Question 6

what bonds are formed between bases

Answer 6

hydrogen bonds

A+T+U form 2 hydrogen bonds
C+G form 3 hydrogen bonds

Question 7

what are the complementary base pairs

Answer 7

C+G
A+T in DNA / A+U in RNA

Question 8

what are the 2 types of bases

Answer 8

purine and pyramidine

Question 9

which bases are purine

Answer 9

A G

Question 10

which bases are pyramidine

Answer 10

C U T

Question 11

what is the difference between purine and pyramidine bases

Answer 11

purine bases are larger due to double C rings

pyramidine bases are smaller due to single C rings

Question 12

how does complementary base pair bonding ensure 2 DNA strands are equidistant

Answer 12

purines bond with pyramidines

as purines are larger and pyramidines are smaller this ensures there is a constant distance between sugar-phosphate backbone

Question 13

how are DNA/RNA sequences read

Answer 13

from 5’ to 3’

Question 14

DNA strands are not described as parallel
- what are they described as and why

Answer 14

• antiparallel
• one strand runs from 5’ to 3’ and the other runs from 3’ to 5’

Question 15

why are DNA strands antiparallel

Answer 15

one strand must be rotated 180 degrees to allow for hydrogen bonding between bases

Question 16

outline the steps involved in DNA extraction with a plant sample

Answer 16

• grind up sample using a pestle and mortar
• mix sample with detergent
• add salt
• add protease
• add ice cold ethanol down the side of the test tube

Question 17

why must the sample be ground during DNA extraction

Answer 17

to break down cell walls

Question 18

why is detergent added during DNA extraction

Answer 18

to break down cell membrane, releasing cell contents

Question 19

why is salt added during DNA extraction

Answer 19

neutralises charges on phosphates in DNA backbone + breaks hydrogen bonds between DNA and water, so it is less soluble

Question 20

why is protease added during extraction of DNA

Answer 20

breaks down histone proteins associated with DNA

Question 21

why is ice cold ethanol added during the extraction of DNA

Answer 21

this causes the DNA to form a white precipitate between the layer of the sample and the ethanol

ice cold as it helps to make DNA more insoluble

Question 22

why must the extraction of DNA be carried out at a low temperature

Answer 22

reduces the rate of enzyme controlled reactions that break down DNA

Question 23

why is it important that cell replication results in 2 genetically identical molecules of DNA

Answer 23

this ensures the continuation of a species

Question 24

why is DNA replication described as being semi conservative

Answer 24

each one of the 2 daughter DNA molecules contains one original strand and one newly synthesised strand

Question 25

outline the steps of DNA replication

Answer 25

• DNA molecule unwinds and hydrogen bonds between bases are broken by DNA helicase, unzipping molecule
• free floating nucleotides in the nucleoplasm pair up with bases on original DNA strands via complementary base pairing
• DNA polymerase forms phosphodiester bonds, reforming sugar-phosphate backbone and molecules retwist to form double helix shapes
• 2 new DNA molecules are produced

Question 26

what are 2 functions of DNA

Answer 26

• storage and transfer of genetic information
• protein synthesis

Question 27

what is the difference between deoxyribose and ribose

Answer 27

deoxyribose has no OH group on carbon 2

Question 28

why is DNA replication important

Answer 28

DNA needs to replicate for mitosis/meiosis

Question 29

what are 3 important features of the DNA code

Answer 29

• degenerate
• non-overlapping
• universal

Question 30

what is a primer

Answer 30

a short piece of RNA or DNA with a complementary sequence to part of the DNA template

Question 31

what is the difference between the leading strand and the lagging strand

Answer 31

the leading strand is built continuously and the lagging strand is built discontinuously

Question 32

why is there 1 leading strand and 1 lagging strand

Answer 32

due to the antiparallel nature of DNA

Question 33

why are primers needed in DNA replication

Answer 33

DNA polymerase requires them in order to bind to the 3’ OH group and begin reforming the sugar-phosphate backbone

Question 34

what does the discontinuous building of the lagging strand lead to the production of

Answer 34

okazaki fragments

Question 35

what are 3 reasons that complementary base pairing important in DNA replication

Answer 35

• reduces occurance of mutations
• allows for the formation of hydrogen bonds that holds strands together
• DNA is replicated without error

Question 36

what are 3 differences between DNA and RNA

Answer 36

DNA is double stranded, RNA is single stranded

DNA has ACTG, RNA has ACUG

DNA is too big to leave the nucleus, RNA is small enough to fit through nuclear pores