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OCR AS/A Level Biology Exam Questions > module 2.3: nucleotides and nucleic acids > Flashcards

module 2.3: nucleotides and nucleic acids Flashcards

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1
Q

name the base represented by the letter T

A

thymine

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2
Q

Put a cross (X) in the box next to each incorrect statement
- the DNA molecule unwinds
- hydrogen bonds between the base pairs break
- free RNA nucleotides join to bases on the exposed DNA strands
- both polypeptide strands act as a template
- hydrogen bonds form between complementary bases
- three hydrogen bonds form between bases A and T
- DNA polymerase links the new nucleotides
- covalent bonds form between the phosphate of one nucleotide and the pentose sugar of the next nucleotide

A
  • free RNA nucleotides join to bases on the exposed DNA strands
  • both polypeptide strands act as a template
  • three hydrogen bonds form between bases A and T
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3
Q

complete the following passage by using the most appropriate terms.
variation can be described as the differences in characteristics between
………………… . the type of variation that is caused by differences in DNA is known as …………………. variation. variation can also be caused
by the …………………… . variation between members of the same species is known as ………………….. variation. evolution depends on variation and …………………. of the best adapted individuals.

A
  • individuals / organisms / species / phenotypes
  • genetic
  • environment
  • intraspecific
  • selection / survival
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4
Q

state the number of DNA nucleotide bases that code for a single amino acid

A

3

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5
Q

there is a maximum of 64 different base combinations in DNA that could each code for an amino acid. how is this number of combinations calculated

A

4 x 4 x 4

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6
Q

twenty different amino acids are commonly used for protein synthesis. in theory, this would need only 20 different base combinations. explain the uses of the remaining 44 combinations

A
  • several, triplet(s) / codon(s) , code for one amino acid
  • (some are used as) start / stop / termination
  • idea that mutation may , not result in change in amino acid / have a neutral effect / result in silent mutation
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7
Q

which nucleotide bases are common to DNA and RNA

A

adenine / A and cytosine / C and guanine / G

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8
Q

describe how a nucleotide base sequence in a gene is used to synthesise a polypeptide

A

TRANSCRIPTION
- DNA / gene , copied / transcribed , into mRNA
- free / activated , (RNA) nucleotides / (RNA) nucleoside triphosphates
- (line up by) complementary base pairing / described
- (to) one / template / reference / sense ,
(DNA) strand
- (catalysed by) RNA polymerase
TRNASLATION
- (mRNA moves to) ribosomes
- tRNA (molecules) bind to mRNA
- anticodon(s) , match / pair with / bind to , codons
- specific / correct , amino acid attached to tRNA
- formation of peptide bond between amino acids

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9
Q

complete the following paragraph by using the most appropriate term(s). a gene is a section of DNA that codes for the production of a ……………. . the molecule that copies a gene and carries the information to a ……………… is called RNA

A
  • polypeptide
  • ribosome
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10
Q

DNA replication takes place during interphase of the cell cycle. it occurs by a semi-conservative mechanism. explain why DNA replication is considered to be semi-conservative

A
  • one strand, from original DNA and one strand newly formed
  • an , (original) strand / polynucleotide , acts as template (for new strand)
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11
Q

explain why complementary base pairing is important in DNA replication

A
  • (DNA) can be replicated without error / same sequence of nucleotides is produced
  • reduces occurrence of mutation
  • allows (re-)formation of , hydrogen / H , bonds
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12
Q

state two ways in which a diagram of part of an RNA molecule would appear different from the DNA molecule shown in Fig. 5.1

A
  • (usually) single stranded / would not have 2 strands
  • uracil / U, instead of thymine / T
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13
Q

the technique of centrifugation used by Meselson and Stahl involves:
* mixing the DNA sample with concentrated sugar solution
* placing the mixture of DNA and sugar solution in test-tubes
* spinning the test-tubes at a very high speed.
suggest three precautions that Meselson and Stahl would have taken in order to ensure that the centrifugation part of their investigation produced valid results

A
  • same concentration of sugar (solution in each tube)
  • same volume of, mixture / solution / sugar solution (in each tube)
  • spin (all tubes) at same , speed / acceleration
  • spin (all tubes) for same (length of) time
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14
Q

name the precise group of carbohydrate molecules of which glucose is an example

A

monosaccharide(s)

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15
Q

deoxyribose is a pentose sugar that is a component of the double-stranded DNA molecule. describe the structural relationship between deoxyribose and the other components of the DNA molecule

A
  • part of nucleotide
  • bonded / joined / attached , to (named) base and phosphate
  • phosphate (joined) to C5 (and C3) / base (joined) to C1
  • (deoxyribose is part of) backbone (of DNA)
  • idea of linking with (second) phosphate on adjacent nucleotide
  • nucleotide is , monomer / repeating unit , of DNA / polynucleotide
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16
Q

describe how the information coded on genes is used to synthesise polypeptides and how these polypeptides control the physical development of an organism

A
  • synthesis
  • DNA, copied into / , mRNA or described
  • transcription / transcribed
  • one strand copied
  • complementary base-pairing
  • triplet code / code read in threes / codon is 3 bases
  • base sequence determines amino acid sequence
  • translation
  • ribosomes
  • role of tRNA described (max 6)
    ROLES OF POLYPEPTIDES
  • (named) structural protein
  • enzymes / catalyse reactions / control metabolism
  • hormones / growth factors
  • receptor proteins
  • adenyl cyclase / cAMP
  • idea of switching genes, on / off
  • homeotic / homeobox, genes or homeodomain proteins
  • idea of master switch gene / one gene turns on/off whole set of other genes /
    cascades of gene switching
  • apoptosis
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17
Q

state the components of a DNA nucleotide

A
  • deoxyribose (sugar)
  • phosphate (group)
  • (nitrogenous / purine or pyrimidine) base / one correctly named base
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18
Q

describe how the structure of RNA differs from that of DNA

A
  • has ribose
  • uracil / U, instead of, thymine / T
  • single stranded
  • 3 forms
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19
Q

before a cell divides, the DNA needs to be accurately replicated. describe how a DNA molecule is replicated

A
  • untwist / unwind
  • unzip / described
  • H bond breaks
  • both strands act as template
  • (aligning of) free (DNA) nucleotides
  • complementary, base / nucleotide, pairing
  • C to G and T to A / purine to pyrimidine
  • hydrogen bonds reform
  • sugar-phosphate back bone forms
  • (using) covalent / phosphodiester, bond
  • semi-conservative replication
  • DNA polymerase
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20
Q

state what a gene codes for

A
  • polypeptide / protein / primary structure / a sequence of amino acids
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21
Q

Suggest how changing the sequence of DNA nucleotides could affect the final product the DNA codes for

A
  • different, sequence of amino acids / primary structure
  • different protein / protein folds up differently / different tertiary structure
  • (product) no longer functions / different function
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22
Q

state the role of a gene

A
  • code for (one or more) polypeptide(s)
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23
Q

explain how the structure of DNA allows replication

A
  • double stranded
  • each / both (strands) act as template hydrogen bonds , easily , break / form , between bases
  • complementary (specified) base , pairing
  • purine (only able to) bind to pyrimidine
    (due to) different sizes of purines and pyrimidines ;
    hydrogen bonding different between A & T and C & G
    or
    3 H bonds between C & G and 2 H bonds between A & T
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24
Q

DNA is found in the nucleus. the molecule is twisted into a ………….. ………….. in which each of the strands are ………….. . it has two ……………………. backbones attached to one another by complementary bases. these bases pair in the centre of the molecule by means of ………….. bonds

A
  • double helix
  • anti-parallel
  • sugar-phosphate
  • hydrogen
25
Q

complete the table, using a letter D, R or B, to show whether each statement applies to:
* DNA only (D)
* RNA only (R)
* both DNA and RNA (B)
- contains thymine - D
- contains ribose
- consists of two chains connected to
each other with hydrogen bonds
- has a sugar-phosphate backbone
- has four different nitrogenous bases
- contains a pentose sugar
- is found in the nucleus and
cytoplasm

A
  • R
  • D
  • B
  • B
  • B
  • R
26
Q

a group of students attempted to extract and purify DNA from a plant in Upper End Meadow. the students used the following steps:
1. mix the plant sample with detergent.
2. add salt.
3. add protease enzyme.
4. spool the DNA precipitate onto a glass rod.
suggest whether this method would successfully extract and purify DNA. justify your conclusion

A

YES
- detergent, breaks / disrupts, (cell) membrane(s) / nuclear envelope OR
detergent, releases contents of, cell / nucleus ✓
- salt, helps DNA, shed water / precipitate ✓
- protease breaks down, histones / proteins around DNA / proteins attached to DNA ✓
NO
- cell walls not broken by abrasion / grinding / blender ✓
- no RNAase added to remove
RNA (from DNA / chromatin) ✓
- no, alcohol / ethanol, added
to, precipitate DNA ✓
- temperature not low to
reduce, enzyme activity / DNA
break down ✓

27
Q

a student tried to extract some DNA from a crushed banana at home. DNA dissolves in water but the student realised that they needed to add something to break open the nuclear envelope to release the DNA. suggest a suitable substance the student could use to release the DNA, and explain why it should work

A
  • detergent (1)
  • works as an emulsifier / attracts phospholipid molecules and water molecules (1)
  • it will break up the plasma /
    nuclear membranes (1)
28
Q

a DNA molecule contains two polynucleotide chains. describe how these two chains are held together

A
  • phosphodiester bonds in,
    backbone / described ✔
  • hydrogen / H, bonds /
    bonding (between chains /
    bases) ✔
  • purine to pyrimidine / A to T
    and C to G ✔
  • ref to correct number of
    bonds between base pairs (A-T
    & C-G) ✔
29
Q

explain how the nucleotides in a DNA molecule are arranged as two polynucleotide strands

A
  • nucleotides joined by phosphodiester bonds ✓
  • hydrogen bonds between,
    complementary / named bases ✓
    3 (polynucleotides) are anti parallel / described ✓
    4 AVP ✓ (eg. . sense / coding, strand is 5’ to 3’ antisense / nonsense / template, strand is 3’ to 5’
30
Q

nucleic acids are made from ……………… monomers. phosphodiester bonds form between the monomers. they consist of a ……………. group between the ………………. molecules, forming the ‘backbone’ of the molecule. in DNA, hydrogen bonding between the two antiparallel …………….. causes the characteristic double helix shape

A
  • nucleotide ✔
  • phosphate ✔
  • pentose ✔
  • strands ✔
31
Q

identify two similarities and two differences between the DNA nucleotide shown in Fig. 24 and a molecule of
ATP

A

BOTH HAVE:
- a pentose (sugar) ✓
- adenine (base) ✓
- phosphodiester bond (between sugar and phosphate) ✓
- an OH group on carbon 3 of the
sugar ✓
- phosphate (group) ✓
ATP HAS:
- two additional phosphates ✓
- deoxyribose replaced by ribose ✓
- an OH group on carbon 2 of the, sugar / ribose ✓

32
Q

DNA is arguably the most important molecule in the whole of biology. when a cell divides an identical copy of its DNA is made in a process called DNA replication. explain how pairing of nitrogenous bases allows identical copies of DNA to be made

A
  • adenine / A pairs with thymine / T and cytosine / C pairs with guanine / G (1)
  • (because of) hydrogen bonding (1)
  • idea that purine can only bind with pyrimidine because they are different sizes (1)
  • idea that if one base is known it
    can pair with only one other
    base (1)
33
Q

state two differences between a molecule of ADP and a DNA nucleotide that contains adenine

A
  • ADP has 2 phosphates whereas DNA nucleotide (with adenine) has 1 phosphate ✓
  • ADP has ribose whereas DNA (nucleotide with adenine) has deoxyribose ✓
    OR
  • ADP has OH on carbon 2 of sugar whereas DNA (nucleotide with adenine) has no OH on carbon 2 of sugar ✓
34
Q

ADP binds with an inorganic phosphate (Pi) to make ATP. name this type of reaction

A
  • condensation ✓
    (accept phosphorylation)
35
Q

DNA replication and transcription are two processes that occur in the nucleus of eukaryotic cells. * compare DNA replication and transcription by describing the similarities and differences between the two processes

A

SIMILARITIES
* DNA unwinds and unzips
* Helicase enzymes
* Template DNA
* Complementary base pairing
* Hydrogen bonds
* Free, activated nucleotides
* Polymerase enzymes
DIFFERENCES
* Only a small section of DNA (where the
gene is located) unzips during
transcription
* Both strands act as templates in
replication
* RNA vs DNA free nucleotides
* RNA vs DNA polymerase
* Different helicase enzymes
* Products are two new daughter strands
of DNA in replication and one mRNA
strand in transcription
* mRNA leaves nucleus whereas the new
DNA strand remains bound to the
template strand

36
Q

name two enzymes involved in DNA replication

A
  • helicase ✓
  • DNA polymerase ✓
  • AVP ✓ e.g. (DNA) ligase
    (DNA) gyrase
37
Q

explain the meaning of the phrase semi-conservative replication

A
  • (new DNA molecule comprises) one, original / old / parent, strand and one new strand ✔
  • each strand (of DNA molecule) acts as a template strand (for a new double helix) ✔
38
Q

DNA ligase is one enzyme involved in the replication of DNA. state two other enzymes involved and describe their functions

A
  • (DNA) helicase ✔ unzips the DNA molecule / breaks hydrogen bonds (between complementary bases)/ separates the (2) strands ✔
  • DNA polymerase ✔ forms phosphodiester bonds / joins (adjacent) nucleotides / forms sugar-phosphate backbone ✔
  • gyrase ✔ unwinds / uncoils, the DNA ✔
39
Q

the tube labelled Generation 0 in Fig. 25 shows a single band of DNA containing bases that contain only the heavy isotope of nitrogen 15N. explain how the results from the other generations provide evidence to support the hypothesis that DNA replication is semi-conservative

A

TUBE WITH GENERATION 1
- shows (new) DNA / band,
contains, light nitrogen / N14 ,
and, heavy nitrogen / N15 ✔
TUBE WITH GENERATION 2
- (new) DNA / band, made from only, light nitrogen / N14 ✔
- so a, light / N14 , strand of DNA must be a, template / parent strand, for the new molecule ✔
TUBE WITH GENERATION 10
- (highest band gets thicker
because) more of the DNA is made from
only, light nitrogen / N14 ✔

40
Q

outline how the process of DNA replication is completed, following the pairing of nitrogenous bases

A
  • (involves) DNA polymerase (1)
  • sugar-phosphate backbone (re)forms / condensation reaction between phosphate and sugar (1)
  • DNA winds into double helix (1)
41
Q

DNA sequences in genes code for polypeptide molecules such as pepsin and titin. explain why a process known as transcription is necessary for polypeptide synthesis

A
  • gene / DNA, copied / transcribed, to (m)RNA ✓
  • (idea that RNA goes to / translation is at) ribosome(s) / RER ✓
  • DNA, is too large to / cannot / is not able to, leave nucleus /cross nuclear envelope / fit through nuclear pores ✓
42
Q

explain how the genetic code in the gene for tubulin codes for the protein tubulin

A
  • 3 bases / triplet, code for 1 (specific) amino acid ✓
  • sequence of, bases / triplets, determines the sequence of, amino acids / primary structure ✓
  • (code) non-overlapping ✓
  • AVP ✓ (e.g. more than one codon codes for an amino acid / degenerate code is, universal / similar in eukaryotes and prokaryotes)
43
Q

suggest two ways tubulin is essential to protein synthesis and protein secretion in eukaryotic cells

A
  • movement of mRNA from nucleus to ribosome ✓
  • movement of polypeptides through the rER ✓
    movement of vesicles from rER
    to Golgi ✓
    movement of vesicles between
    cisternae of Golgi (cis to trans
    face) ✓
    movement of secretory vesicles
    from Golgi to cell surface
    membrane✓
44
Q

which of the following statements, A to D, about the nature of the genetic code is incorrect?
A. it is a degenerate code
B. it is a triplet code
C. it is overlapping
D. it is universal

A

C. it is overlapping

45
Q

the diagram below shows an organic molecule. what bond is formed when the molecule is polymerised?
A - ester
B - glycosidic
C - peptide
D - phosphodiester

A

D - phosphodiester

46
Q

which of the following statements describes an organelle which is not membrane bound
A - contains cristae
B - modifies and packages proteins
C - contains digestive enzymes
D - is made of rRNA and protein

A

D - is made of rRNA and protein

47
Q

the following statements are about the structure of DNA. which of the following statement(s) is / are true?
statement 1: purine bases pair with pyrimidine bases
statement 2: phosphodiester bonds link adjacent nucleotides
statement 3: there are always equal amounts of adenine and guanine
A. 1, 2 and 3
B. Only 1 and 2
C. Only 2 and 3
D. Only 1

A

B. Only 1 and 2

48
Q

which of the statements, A to D, shows that the genetic code is degenerate?
A - CCA and CCT code for proline
B - rRNA is manufactured in the nucleolus
C - tRNA is not complementary to DNA
D - uracil is not found in DNA

A

A - CCA and CCT code for proline

49
Q

which of the following processes occur during DNA replication?
1 breakage and (re)formation of phosphodiester bonds
2 breakage and (re)formation of hydrogen bonds
3 alignment of free nucleotides with their complementary bases
A - 1, 2 and 3
B - only 1 and 2
C - only 2 and 3
D - only 1

A

C - only 2 and 3

50
Q

which of the following statements, A to D, about DNA replication is correct?
A - RNA will bind to DNA through complementary base-pairing
B - the distance between the strands in the double helix will always be the same
C - the proportion of adenine in a nucleic acid will always equal the proportion of guanine
D - the formation of phosphodiester bonds will occur in the same direction on each strand during DNA replication

A

D - the formation of phosphodiester bonds will occur in the same direction on each strand during DNA replication

51
Q

DNA is made up of two polynucleotide chains. which of the bonds, A to D, forms between two nitrogenous bases holding the two polynucleotide chains
together
A - phosphodiester
B - ionic
C - covalent
D - hydrogen

A

D - hydrogen

52
Q

which statement, A to D, describes the function of DNA polymerase
A - break the hydrogen bonds between complementary bases
B - make phosphodiester bonds between adjacent nucleotides
C - make phosphodiester bonds between polynucleotides
D - make the hydrogen bonds between complementary bases

A

B - make phosphodiester bonds between adjacent nucleotides

53
Q

which of the following statements is/are evidence that DNA replication is semiconservative?
1 - after one replication, the number of adenine nucleotides is equal to the number of guanine nucleotides.
2 - after two replications, two DNA molecules have one original and one new strand, and two DNA molecules have two new strands.
3 - after three replications, there are eight DNA molecules, only two of which have strands from the original DNA.
A - 1, 2 and 3
B - only 1 and 2
C - only 2 and 3
D - only 1

A

C - only 2 and 3

54
Q

during DNA replication, DNA polymerase can only work in one direction – from the 3’ end to the 5’ end.
this means that the lagging strand has small gaps left in the backbone. DNA ligase works to seal these gaps.
which of the options, A to D, identifies the bond formed?
A - hydrogen bond
B - phosphodiester bond
C - glycosidic bond
D - peptide bond

A

B - phosphodiester bond

55
Q

which of the options, A to D, contains the correct definitions for non overlapping and degenerate code?
A - each nucleotide is only part of one triplet of bases and the molecule breaks down easily
B - the genes follow straight after each other and the molecule breaks down easily
C - each nucleotide is only part of one triplet of bases and more than one triplet codes for a specific amino acid
D - the genes follow straight after each other and more than one triplet codes for a specific amino acid

A

C - each nucleotide is only part of one triplet of bases and more than one triplet codes for a specific amino acid

56
Q

a standard method can be used to extract DNA from the nuclei of cells in kiwi fruit. the statements below list some of the steps involved in this method.
which statement is not correct
A - chop the kiwi fruit to break open cell membranes
B - add detergent to dissolve nuclear membranes
C - add protease to digest histone proteins
D - pour ice cold ethanol onto filtrate to precipitate DNA

A

A - chop the kiwi fruit to break open cell membranes

57
Q

name the purine bases

A
  • adenine
  • guanine
58
Q

a sample of DNA containing only one isotope of nitrogen, 15N, was incubated with nucleotides containing only the 14N isotope along with the enzymes needed for replication. which of the following diagrams would represent the resulting DNA after one round of replication

A

A

59
Q

a length of DNA has the base sequence AATCGCGGTCGCTCA. select the row that shows the correct complementary DNA strand and the sequence of mRNA made during transcription of the DNA sequence above
A - AATCGCGGTCGCTCA & UUAGCGCCAGCGAGU
B - TTAGCGCCAGCGAGT & UUAGCGCCAGCGAGU
C - TTAGCGCCAGCGAGT & TTAGCGCCAGCGAGT
D - TTAGCGCCAGCGAGT & AAUCGCGGUCGCUCA

A

B - TTAGCGCCAGCGAGT & UUAGCGCCAGCGAGU

OCR AS/A Level Biology Exam Questions (13 decks)

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