Biological molecules - Nucleotides and Nucleic acids

Question 1

are nucleic acids polymers

Answer 1

yes

Question 2

what are the monomer units in nucleic acids

Answer 2

nucleotides

Question 3

what are the subunits in nucleotides

Answer 3

• phosphate group
• pentose sugar
• nitrogenous base

Question 4

how are the subunits in a nucleotide joined

Answer 4

by covalent bonds

Question 5

how many nitrogenous bases are there for DNA

Answer 5

four

Question 6

how are the nitrogenous bases for DNA grouped

Answer 6

two are purine (two rings) and two are pyrimidine (one ring)

Question 7

what are the four bases in DNA and which are purine or pyrimidine

Answer 7

purine bases: adenine, guanine
pyrimidine bases: thymine, cytosine

Question 8

how do the bases in DNA go together

Answer 8

A and T, C and G

Question 9

what are phosphorylated nucleotides

Answer 9

contain more than one phosphate group

Question 10

give two examples of phosphorylated nucleotides and explain their function

Answer 10

adenosine triphosphate (ATP) and adenosine diphosphate (ADP).
these molecules are the “energy currency” of cells. the hydrolysis of ATP to ADP + Pi releases energy

Question 11

how is ATP made

Answer 11

respiration

Question 12

describe the structure of ATP

Answer 12

three phosphates (attached to carbon 5 ), ribose, adenine

Question 13

how many types of nucleic acids are there, and what are they

Answer 13

2
- deoxyribonucleic acid (DNA)
- ribonucleic acid (RNA)

Question 14

what do nucleic acids do

Answer 14

they are molecules that hold the coded information required to build an organism and keep it running

Question 15

is DNA a polymer

Answer 15

yes, the monomers are nucleotides

Question 16

how is DNA formed

Answer 16

the nucleotides join up between the phosphate group on one nucleotide and the carbon 3 of the sugar of another via a condensation reaction. this forms a phosphodiester bond

Question 17

describe the structure of DNA

Answer 17

• DNA consists of 2 polynucleotide strands
• the strands are made of a sugar-phosphate backbone attached to nitrogenous bases
• its shape is a twisted double helix
• the strands run in opposite directions (antiparallel)
• hydrogen bonds form between the bases - 2 bonds between A and T and 3 bonds between C and G

Question 18

how many bonds form between the bases

Answer 18

2 bonds between A and T and 3 bonds between C and G

Question 19

how do bases join

Answer 19

hydrogen bonds form between the bases on the two polynucleotides, this stabilises the structure

Question 20

why is it important for the DNA molecule to be stable

Answer 20

it needs to be replicated

Question 21

what are the rules for complementary base pairing

Answer 21

purine always paired with pyrimidine
A-T (2 hydrogen bonds)
C-G (3 hydrogen bonds)

Question 22

what is the sugar in DNA

Answer 22

deoxyribose

Question 23

explain how the structure of DNA is ideally suited to its role

Answer 23

• base sequence used as code
• polymer - lots of information
• double stranded - stable, accurate replication
• complementary base pairing allows it to be copied and transcribed
• hydrogen bonds can be broken/made so can be copied and read easily

Question 24

describe DNA in eukaryotes

Answer 24

• the majority of DNA is found in the nucleus
• DNA is wound around histone proteins, making chromosomes
• there are also loops of DNA, without histones, inside mitochondria and chloroplasts

Question 25

describe DNA in prokaryotes

Answer 25

• DNA is a loop within the cytoplasm (no nucleus)
• it is “naked” not wound around histone proteins
• small loops called plasmids often present

Question 26

describe the general method for extracting DNA

Answer 26

• add detergent and salt (also maybe protease to denature histones) to a zip lock bag, then add the fruit and remove air
• mash
• filter
• transfer to boiling tube and pour chilled ethanol down the side

Question 27

why must DNA be copied each time a cell divides

Answer 27

so that each new daughter cell has the full set of instructions

Question 28

when does DNA replication take place

Answer 28

during interphase in the cell cycle before mitosis

Question 29

describe chromosomes in eukaryotes after replication

Answer 29

each chromosome is composed of 2 chromatids held together at the centrosome

Question 30

describe the products of DNA replication

Answer 30

2 DNA molecules identical to each other. each molecule contains one of the old strands and one new strand. this is why it is called semi-conservative replication

Question 31

what kind of replication is DNA replication

Answer 31

semi-conservative

Question 32

what is the first step of DNA replication

Answer 32

DNA untwists and unzips (the hydrogen bonds between the bases are hydrolysed). this is catalysed by DNA helicase

Question 33

what is the second step of DNA replication

Answer 33

free nucleotides in the nucleoplasm bind at the exposed complementary bases

Question 34

what is the third step of DNA replication

Answer 34

hydrolysis releases the extra phosphate groups from the nucleotides and supplies energy to form the phosphodiester bonds between the sugar of one nucleotide and the phosphate groups of the adjacent nucleotide.
this is catalysed by DNA polymerase

Question 35

what direction does DNA polymerase work in

Answer 35

5’ to 3’ direction

Question 36

what is the fourth step of DNA replication

Answer 36

the leading strand is synthesised continuously as DNA polymerase keeps working in the 5’ to 3’ direction as new bases are exposed
the lagging strand is synthesised in fragments (Okazaki fragments) joined using DNA ligase enzymes