nucleic acid

Question 1

describe nucleic acids

Answer 1

large molecules discovered in cell nuclei

two types:

DNA
RNA

large polymers formed from nucleotides (monomers) linked together in a chain by condensation to form polynucleotides

Question 2

describe the structure of a nucleotide

Answer 2

phosphate group
inorganic and negatively charged

bonded covalently to a

pentose monosaccharide (5 carbon atoms)

nitrogenous base
organic
one-two carbon rings

Question 3

describe the formation of phosphodiester bonds

Answer 3

occurs by the removal of a water molecule when 2 hydroxyl groups from 2 different nucleotides bond with a phosphate group in a condensation reaction

Question 4

what do phosphodiester bonds between the phosphate and the deoxyribose (pentose) sugar form

Answer 4

long, strong sugar phosphate backbone

Question 5

what are the two types of bases?

Answer 5

pyrimidines
contain single C ring structures – thymine (T) and cytosine (C)

purine
contain double C ring structures – adenine (A) and guanine (G)

Question 6

describe the formation of a double helix

Answer 6

DNA molecule made of 2 strands (held by hydrogen bonds between bases) of polynucleotides coiled into a helix

two parallel strands arranged to run in opposite directions (anti parallel)

Question 7

describe complementary base pairing

Answer 7

A + T form 2 hydrogen bonds and join with each other
C + G form 3 hydrogen bonds and only bind to each other

this means there will always be an equal amount of A&T and C&G

Question 8

what does this base pairing mean?

Answer 8

arrangement between pyrimidine and purine bases mean there’s a constant distance between he DNA backbone forming parallel polynucleotide chains

Question 9

describe the structure of RNA

Answer 9

short section of DNA molecule (corresponding to a single gene) that gets transcribed into

mRNA
polymer
short than a chromosome

Question 10

describe two differences between RNA and DNA nucleotides

Answer 10

RNA contains a ribose, whereas a DNA contains a deoxyribose

if the base was a T, this will be replaced by a uracil (U) base in RNA

uracil is a pyrimidine base which forms 2 hydrogen bonds between adenine

Question 11

describe the function of RNA

Answer 11

RNA polymers leave nucleus and travel to ribosomes for protein synthesis

after protein synthesis, RNA molecules are degraded in cytoplasm

phosphodiester bonds are hydrolysed
RNA nucleotides released and reused

Question 12

how is the structure of DNA ideally fit to its function?

Answer 12

polymer - contains a lot of information

base sequence is used as a code

doubled stranded - molecule is stable and allows for accurate replication

Question 13

a sample of DNA was tested and 21% of total bases present were adenine

calculate the percentage of the other three bases present in the sample

Answer 13

21% - adenine
21% - thymine

29% - cytosine
29% - guanine

Question 14

genes are

Answer 14

sequences of nucelotides

Question 15

what is a nucleotide

Answer 15

nitrogen-containing organic substance forming the basis of DNA & RNA

Question 16

what is the function of ATP?

Answer 16

produced in respiration

provides energy for cellular reactions

Question 17

what does ATP stand for and what does this suggest about its structure?

Answer 17

adenosine triphosphate

adenine base

binded to a ribose sugar

which binds to three inorganic phosphate groups

Question 18

how is ADP formed?

Answer 18

hydrolysis of ATP –>

forms ADP + an inorganic phosphate group

releases 30.5 kJ

Question 19

how is DNA packaged

Answer 19

as chromosomes

eukaryotic DNA associates with histones to form chromatin

chromatin coils and condenses to form chromosomes

Question 20

what does ADP stand for

Answer 20

Adenosine diphosphate

Question 21

what’s a codon

Answer 21

sequence of three nucleotides

codes for an amino acid

Question 22

describe the steps of semi conservative replication

Answer 22

double helix structure unwinds and separates into 2 strands
each strands acts as a template for creation of new DNA molecules

hydrogen bonds holding comp bases break

free nucleotides pair up with exposed bases and form hydrogen bonds

new nucleotides join adjacent nucleotides with phosphodiester bonds

leads to formation of 2 new DNA molecules
each molecule has the old (template) strand and the new strand

Question 23

name the enzyme used to cause the strands of DNA to separate

Answer 23

DNA helicase

Question 24

describe the function of DNA polymerase

Answer 24

enzyme

catalyses the synthesis of DNA strands from free nucleotides

Question 25

what can DNA polymerase only do?

Answer 25

bind to the 3’ (OH) end

They always need a template

They proofread
removing the vast majority of “wrong” nucleotides that are accidentally added to the chain

Question 26

describe the leading strand

Answer 26

strand unzipped from the 3’ end which can be continually replicated as DNA molecule unzips

(continuous replication)

Question 27

describe the lagging strand

Answer 27

other strand unzipped from the 5’ end

so DNA polymerase has to wait for a section of strand to unzip and then work back along the strand

DNA is produced in Okazaki fragments
(which then have to be joined by DNA ligase to remove nicks)

(discontinuous replication)

Question 28

what is the replication fork?

Answer 28

point at which two DNA strands separate

Question 29

how does the DNA polymerase at the lagging strand initiate DNA synthesis

Answer 29

from an RNA primer (made by primase complex)

polymerase elongates strand opposite to the fork

newly synthesised lagging strand fragment loops out between the polymerase and the fork

once polymerase completes an okazaki fragment
it dissociates from the DNA template

a new primer produces at the fork
the polymerase reassociates with the template at this position

Question 30

describe a gene

Answer 30

section of DNA containing the complete sequence of bases to code for an entire protein