2.3 nucleic acids and enzymes Flashcards

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1
Q

what is the structure of nucleotides

A

a phosphate
5 carbon sugar
nitrogenous base

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2
Q

name the pentose sugars in RNA and in DNA

A

deoxyribose
ribose

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3
Q

describe how polynucleotide strands are formed and broken down

A

condensation reactions form strong phosphodiester and glycosidic bonds

hydrolisis reactions use a molecule of water to break these bonds

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4
Q

describe the structure of DNA

A

molecule twists to form a double helix of 2 deoxyribose polynucleotide strands that are anti parallel to each other

a-t
c-g

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5
Q

name the purine bases and describe their structure

A

adenine
guanine
two ring molecules

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6
Q

name the pyrimidine bases and describe their structure

A

thymine
cytosine
uracil
one ring molecules

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7
Q

why is DNA replication described as semi conservative

A

strands from original DNA molecule act as a template

new DNA molecule contains 1 old strand and 1 new strand

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8
Q

explain the role of helicase in semi conservative replication

A

breaks hydrogen bonds between base pairs to form 2 single strands, each of which can act as a template

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9
Q

how is a new strand formed during semi conservative replication

A

DNA gyrase unwinds and helicase unzips DNA

primase adds a primer so that DNA polymerase knows where to start adding nucleotides

ligase sticks together the fragments

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10
Q

what is the lagging strand

A

DNA polymerase only goes in the 5’3’ direction so okozaki fragments are made in the lagging strand and stuck together by ligase

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11
Q

identify features of genetic code

A

non overlapping - each triplet is only read once

degenerate - more than one triplet codes for the same amino acid (64 possible triplets for 200 amino acids)

universal - same bases and sequences used by all species

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12
Q

how does a gene determine the sequence of amino acids in a protein

A

consists of base triplets that codes for specific amino acids

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13
Q

describe how DNA could be purified through precipitation

A

add ethanol and salt to aqueous solution, nucleic acids precipitate out of solution

centrifuge to obtain a pellet of nucleic acid then wash and centrifuge again

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14
Q

what does transcription produce and where does it occur

A

produces mRNA and occurs in the nucleus

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15
Q

outline the process of transcription

A

RNA polymerase binds to the DNA strand and unwinds a short section

this then travels along the DNA strand building an RNA molecule from the template strand

splicing removes non-coding strands of mRNA (introns)

mRNA leaves through the nuclear pores and attaches to the ribosomes

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16
Q

what does translation produce and where doe it occur

A

produces proteins and occurs in the cytoplasm on ribosomes

17
Q

outline the process of translation

A

tRNA carries specific individual amino acids
tRNA carries an anti codon that matches up to the corresponding bases on mRNA

process continues to form polypeptide chain until ‘stop’ codon is reached

18
Q

what is a mutation

A

an alteration to the DNA base sequence

19
Q

when does DNA replicate

A

during interphase

20
Q

describe enzymes

A

biological catalysts used to spead up reactions

21
Q

what is the difference between intra and extracellular enzymes

A

intracellular enzymes are inside the cell e.g DNA polymerase
whereas extracellular enzymes are outside the cells e.g. protease

22
Q

define turnover number

A

number of reactions an enzyme can catalyse per second

23
Q

define anabolic reaction

A

building up

24
Q

define catabolic reactions

A

breaking down

25
Q

describe the lock and key theory

A

substrate molecules fit into the active site and are then released

26
Q

describe the induced fit hypothesis

A

when the substrate molecules fit into the enzymes active site, the active site changes shape slightly to mould itself around the substrate molecule