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a-level biology - mr hedditch > topic two - nucleic acids - mr hedditch > Flashcards

topic two - nucleic acids - mr hedditch Flashcards

1
Q

state the two types of nucleic acids?

A

DNA – deoxyribonucleic acidcontains the pentose sugardeoxyribose

RNA – ribonucleic acidcontains the pentose sugar
ribose

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2
Q

what does each DNA nucleotide contain?

A

a phosphate group
a deoxyribose sugar molecule (pentose – 5C)
one of four nitrogenous bases

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3
Q

what are the four nitrogenous bases in DNA?

A

adenine (A)
thymine (T)
cytosine (C)
guanine (G)

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4
Q

what are nucleotides monomers of?

A

nucleic acids

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5
Q

how are the tree subunits (phosphate, deoxyribose, nitrogenous base) joined together?

A

joined by covalent bonds formed by condensation reactions

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6
Q

what different about the RNA to DNA?

A

RNA has a ribose sugar and instead of thymine its uracil

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7
Q

state the similarity between DNA and RNA?

A

they are both joined by covalent bonds and formed by a condensation reaction

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8
Q

are DNA purines or pyrimidines and why?

A

they are purine bases because they have two carbon-nitrogen rings, joined together

these are

adenine
guanine

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9
Q

are RNA purines or pyrimidines and why?

A

they are pyrimidine bases because they have a single carbon-nitrogen ring (smaller than a purine base)

these are

cytosine
thymine (DNA only) /Uracil (RNA only)

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10
Q

draw the simple diagram of a RNA nucleotide with any one of the bases?

A

check in book or olc

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11
Q

draw the simple diagram of a DNA nucleotide with any one of the bases?

A

check in book or olc

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12
Q

define a phosphorylated nucleotide?

A

a nucleotide with one or more phosphate groups added to it

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13
Q

state the two types of phosphorylated nucleotides and how many phosphate groups they contain?

A

ADP – adenosine diphosphate (two phosphate groups)

ATP – adenosine triphosphate (three phosphate groups)

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14
Q

what makes up the base and the sugar of ADP & ATP?

A

both molecules have the nitrogenous base adenine

and the pentose sugar ribose

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15
Q

draw the simple diagram for ADP and ATP?

A

check in book or on the olc

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16
Q

define ATP?

A

universal energy source meaning it does the same job and production in all living specimens

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17
Q

how is ATP produced?

A

through a series of oxidation reactions that break down food

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18
Q

why is ATP continuously hydrolysed?

A

so ADP can be released and than re-synthesised

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19
Q

can ATP be transported from cell to cell and why?

A

no, it must be used in the cell in which it’s made

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20
Q

what is ATP made of?

A

three phosphate groups and 2 high energy bonds

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21
Q

draw the simple diagram of ATP and ADP?

A

ATP is three phosphate groups

ADP is two phosphate groups

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22
Q

how is an inorganic molecule produced?

A

the hydrolysis of ATP to ADP is catalysed by the enzyme ATPase
this release energy as well as an inorganic molecule

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23
Q

what does jointing nucleotides form?

A

polynucleotides

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24
Q

what happens in respiration (ATP)?

A

ADP is converted back to ATP by adding a phosphate group

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25
Q

how is a phosphate bond formed?

A

a condensation reaction takes place between the phosphate group of one nucleotide and the sugar molecule of a second nucleotide

26
Q

what is base pairing and why does this happen?

A

A & T
And
C & G
will always pair up

because A&T have have 3 hydrogen bonds and C&G have two hydrogen bonds

27
Q

what does the high number of hydrogen bonds do to DNA?

A

it makes it a very stable structure

28
Q

describe the structure of a double strand?

A 
“antiparallel”
This refers to the 
fact that the sugar phosphate backbones 
run parallel to each 
other but in opposite 
directions
29
Q

what gives the sugar phosphate backbone?

A

phosphodiester bonds

30
Q

draw the simple production of phosphorylation?

A

check with the olc

31
Q

what is the amount of energy released when ATP is hydrolysed to ADP?

A

releases a large amount of energy (30.6kJ mol-1)

32
Q

what phase does DNA replication occur in?

A

interphase

33
Q

why is it important for DNA to be copied accurately?

A

so that the new cells will contain the correct genes to function properly and to produce the correct protein

34
Q

why must chromosomes be copied before mitosis?

A

so that the new cells contain genetic information

35
Q

state the five stages of DNA replication?

A

gyrase causes the double helix to unwind

hydrogen bonds between bases are broken by helicase to separate the two strands, which
can act as templates

free nucleotides align next to the exposed bases according to the complementary base-pairing rule

hydrogen bonds form between the free nucleotides and nucleotides of the original strands

DNA polymerase forms phosphodiester bonds between the phosphate of one nucleotide
and the deoxyribose sugar of the next nucleotide, sealing the sugar-phosphate backbone

36
Q

Why is DNA replication described as “semi-conservative”?

A

this is because the two original “parent” strands act as templates for the formation of new strands.

each replicated molecule contains one old strand and one new strand

37
Q

describe what the enzyme ‘gyrase’ does in DNA replication?

A

unwinds the double helix

38
Q

describe what the enzyme ‘helicase’ does in DNA replication?

A

breaks the hydrogen bonds between the two parental strands of DNA, at a number of different points called replication forks

39
Q

describe what the enzyme ‘polymerase’ does in DNA replication?

A

joins the nucleotides in the new strand together (makes phosphodiester bonds) to form a sugar-phosphate backbone

40
Q

is DNA replication accurate and why?

A

DNA replication is very accurate – this is essential for

genes to be conserved, and is ensured through the action of proof-reading enzymes

41
Q

name the three types of evidence for semi-conservative replication and what they are?

A

semi-conservative – the DNA molecule splits and each strand is replicated. Each of the two new molecules contains one strand of original material and one strand
of new material

conservative - parental DNA remains intact and a separate daughter copy is built out of new molecules. Of the two molecules present, one is the original and one is entirely new material

dispersive – the parental DNA is broken down and the nucleotides replicated before being randomly dispersed throughout the new molecules. The new molecules contain both new and original material but not necessarily in equal amounts

42
Q

what does exonuclease do in DNA replication?

A

it removes all the RNA which is then filled with DNA

43
Q

define gene?

A

a gene is a length of DNA that codes for a polypeptide

44
Q

why does each gene contain a sequence of DNA triplets?

A

it determines the amino acid sequence (or primary structure) of a protein

45
Q

why must a copy of each gene be transcribed into a length of mRNA?

A

the instructions contained in the genes cannot pass out of the nucleus

46
Q

define a codons?

A

a codon is a set of three adjacent nucleotides (bases) on a strand of
mRNA

each codon specifies for one particular amino acid

47
Q

what does the order of the codons along the mRNA strand determines?

A

determines the

sequence of the amino acids in the polypeptide

48
Q

why is the genetic code described as universal?

A

because the same DNA bases (or mRNA codons)

code for the same amino acids in almost all organisms

49
Q

why are there three nucleotides in a codon?

A

There are four bases in DNA:

– adenine, guanine, thymine and cytosine

clearly, it is not possible to have one base
coding for each of the 20 different amino acids

similarly, using two bases would be insufficient
– would only code for 16 different amino acids

using three bases gives 64 possible unique
combinations - more than enough!

the triplet code has spare coding capacity – i.e. there
are more unique codons (64) than there are amino acids to
be coded for (20)

therefore it is possible for several codes to be used to
specify the same amino acid

– e.g. phenylalanine can be coded for by AAA and AAG
– e.g. leucine can be coded for by AAT, AAC, GAA, GAG,
GAT and GAC

because of this, the code is described as degenerate

50
Q

define degenerate?

A

degenerate refers to a code in which several
code words have the same meaning. The genetic code is degenerate because there are many instances in which different codons specify the same amino acid

51
Q

what are the three forms of RNA?

A

mRNA

messenger RNA
a “copy” of the DNA base sequence of a gene complementary to one strand of the DNA (template
strand). The coding sequence of the mRNA determines
the amino acid sequence in the polypeptide that is
produced
single-stranded, with uracil in place of thymine

rRNA
ribosomal RNA
ribosomes are made of rRNA and protein (two sub-units)

tRNA
transfer RNA
small molecule ~ 80 nucleotides
hydrogen bonds make a stable
clover-leaf shaped structure
20 types – one for each of the different amino acids
delivers (transfers) amino acids to growing polypeptide chains in the ribosome in the specific order directed by mRNA

52
Q

state the processes of transcription?

A

the DNA double helix “unzips” as hydrogen bonds
between complementary bases break (due to helicase) and the two polynucleotide strands separate

one DNA strand acts as a template. Free RNA nucleotides
complementary base-pair to the exposed bases on this strand by
forming hydrogen bonds. mRNA contains U in place of T
RNA polymerase forms phosphodiester bonds between the
sugar and phosphate parts of the RNA nucleotides

the mRNA detaches from the template strand of the DNA

the two DNA strands join together by complementary base
pairing (hydrogen bonds reform) and the DNA molecule winds
back up into a helix

53
Q

ways transcription is similar to DNA replication?

A

the DNA molecule unwinds and unzips

helicase is involved in breaking hydrogen bonds

exposed bases act as a template for the formation
of a new polynucleotide strand

complementary base pairing ensures that the
message is transcribed accurately

the free nucleotides joining the new polypeptide
chain are joined together by phosphodiester bonds

54
Q

ways transcription is different from DNA replication?

A

only one DNA strand, the template strand, is copied
(in DNA replication both strands act as templates)

RNA polymerase joins the sugar-phosphate
backbone (not DNA polymerase)

mRNA is single-stranded and a relatively short
molecule with uracil in place of thymine
 Only a single gene is transcribed, whereas in DNA
replication the whole chromosome is copied

55
Q

what happens in the move from transcription to translation?

A

mRNA moves out through a nuclear pore and attaches to a

ribosome

56
Q

what does tRNA transport?

A

transports amino acids to the ribosome for incorporation into a polypeptide chain

57
Q

what do hydrogen bonds between the complementary bases do in tRNA?

A

stabilise the clover-leaf shape

58
Q

what two things does tRNA have?

A

an anticodon that is complementary to a codon on the mRNA

three unpaired bases to which a specific amino acid can be attached (called the attachment site)

59
Q

state what takes place in translation?

A

during translation, mRNA enters the groove between the small and large ribosomal subunits

the ribosome is large enough for two codons to fit side by side

the very first codon is always the start codon AUG
(codes for methionine)

the anticodon of a tRNA molecule carrying methionine
hydrogen bonds to the first codon to start translation

a second tRNA molecule, carrying the second amino acid coded for, hydrogen bonds to the second codon

a peptide bond is formed between the two amino acids through a condensation reaction

the ribosome moves three bases (one codon) along the mRNA so that another codon is exposed

a third tRNA brings another amino acid which is added
to the dipeptide and so the process continues until a
termination or stop codon (UAA, UAG or UGA) is
reached

there is no tRNA for stop codons, so the polypeptide
chain and mRNA are released from the ribosome
translation takes place in the cytoplasm at the
ribosomes

60
Q

what are the two subunits in translation?

A

a large subunit and a small
subunit, bound together with the aid of magnesium ions

– with a groove between them in which the mRNA fits

61
Q

study the transcription/translation grid sheet?

A

in biology folder

a-level biology - mr hedditch (5 decks)

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