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Nucleic Acids Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

describe the basic structure of a nucleotide.

A

a phosphate group, linked to a deoxyribose (or ribose) sugar by a phosphodiester bond to carbon 4. carbon 1 of the sugar bonds to the nucleotide - A,T,C,U,G.

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2
Q

state the two main types of nucleic acid.

A

DNA and RNA.

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3
Q

describe the similarities and differences between RNA and DNA.

A

similarities: - both have a phosphate group, a sugar and nitrogenous base
both have four different bases
both are polymers, macromolecules and are nucleic acids.
differences: RNA has Uracil instead of Thymine
RNA has the sugar ribose not deoxyribose
RNA is single stranded whereas DNA is double stranded.

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4
Q

what is the difference between ribose and deoxyribose?

A

deoxyribose has one less oxygen. on Carbon 2 there is an H rather than an OH group.

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5
Q

list the five possible nitrogenous bases.

A 
Adenine
Guanine
Cytosine
Thymine
Uracil.
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6
Q

what are the two types of nitrogenous base and which bases belong to each?

A

Purines: (larger)

  • Adenine
  • Guanine

Pyramidines (smaller)

  • Cytosine
  • Thymine
  • Uracil
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7
Q

define the term monomer.

A

a single unit that joins with others to become a polymer

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8
Q

define the term polymer.

A

a long, repeated chain of monomers.

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9
Q

define the term nucleic acid.

A

molecules (DNA or RNA) that carry the instructions to make that organism. they are formed from the monomer, nucleotides.

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10
Q

define the term polynucleotide.

A

a polynucleotide is the polymer of nucleotide. meaning it is a string of nucleotides within a nucleic acid molecue.

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11
Q

define the term nucleotide.

A

the monomer of nucleic acids, consisting of a phosphate group, sugar molecule and nitrogenous base.

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12
Q

define the term phosphodiester bond.

A

the bond between the phosphate group and the sugar molecule of the nucleotide.

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13
Q

state the name of the reaction that joins nucleotides together.

A

condensation reaction

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14
Q

state the name of the reaction that breaks phosphodiester bonds.

A

hydrolysis reaction.

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15
Q

state the 3 main types of activity for which cells require energy.

A
  • protein synthesis
  • active transport
  • movement (of cytoskeleton etc)
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16
Q

describe the structure of ATP.

A

3 phosphate groups, bonded to a ribose sugar with adenine as the nitrogenous base.

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17
Q

describe the structure of ADP.

A

2 phosphate groups, bonded to a ribose sugar, with adenine as the nitrogenous base.

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18
Q

name two similarities between RNA/DNA and ATP.

A
  • both contain a pentose sugar

- all contain adenine as a base

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19
Q

name two differences between RNA/DNA and ATP.

A
  • ATP has three phosphate groups rather than one

- ATP has just one base, both DNA and RNA contain 4

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20
Q

describe how ATP releases releases energy.

A

it takes a relatively small amount of energy to break the bond holding the 3rd phosphate onto the ATP molecule, but the energy released from the phosphate then bonding to something else is relatively large. this is called a coupled reaction. this is a hydrolysis reaction catalysed by ATPase.

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21
Q

describe the cycle between ATP and ADP.

A

ATP is hydrolysed by ATPase and the terminal phosphate is removed. at this point energy (around 31kj) is released for the cell to use. ADP turns back into ATP through a process of phosphorination or condensation. catalysed by ATP synthase. the terminal phosphate is added back on by glucose and happens during respiration. energy is released from the organic substrate during respiration.

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22
Q

state 5 properties of ATP and why they make it a good energy transfer molecule.

A
  • small: moves easily in and out of cells
  • water soluble: processes requiring ATP happen in aqueous places
  • phosphate bonds: intermediate amount of energy
  • releases energy in small quantities: energy therefore not wasted in heat
  • easily regenerated: can be recharged with heat.
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23
Q

define the term phosphorylation.

A

the addition of a phosphate group

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24
Q

define the term complementary base pairing.

A

the bases form hydrogen bonds between them to keep the two backbones together. the bases only bond in a certain way. A-T G-C

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25
Q

define the term sugar-phosphate backbone.

A

the two external parts of DNA that form the helix shape, enclosing and protecting the nitrogenous bases.

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26
Q

define the term antiparallel.

A

each strand of DNA has a 3’ end (hydroxyl) and a 5’ end (phosphate) the two strands form in opposite directions so they are called antiparallel

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27
Q

define the term double helix.

A

the two strands of polynucleotides each form a helix shape, wrapped around each other and connected by hydrogen bonds this is called a double helix.

28
Q

define the term strand

A

one strand of DNA is one polynucleotide chain.

29
Q

state the complementary base pairing rules.

A

base pairs are held together by hydrogen bonds.
G-C - three hydrogen bonds
A-T - two hydrogen bonds
RNA: A-U

30
Q

why does DNA have equal amounts of A and T and C and G?

A

because A only pairs with T and G only pairs with C. so they essentially come in pairs.

31
Q

how are purines and pyramidines arranged in DNA.

A

purines and pyramidines only pair with each other. a purine can only bond to a pyramidine. so there are also equal amounts of each in a DNA molecule.

32
Q

explain the significance of DNA having many Hydrogen bonds between base pairs.

A
  • it holds the structure together and maintains the order of the base pairs which is important for its function in protein synthesis
  • it means that individual bonds can be broken to separate the two strands for replication etc.
33
Q

explain the significance of DNA being double stranded.

A

bases on the inside are protected from chemical damage or physical force.

34
Q

explain the significance of DNA being a long molecule.

A

more genetic information can be stored in the molecule.

35
Q

explain the significance of DNA being a helix shape.

A

it’s more contained/compact so more DNA can fit into each cell

36
Q

explain the significance of DNA having bases that form a base sequence.

A

each base sequence codes for a specific order of amino acids in a polypeptide chain.

37
Q

why is DNA replication necessary?

A

organisms need to produce new identical cells for growth and repair of tissues. for these cells to be identical they must contain the same DNA. so the DNA replicates and doubles itself so that each new cell has identical genetic material.

38
Q

what is meant by the term ‘semi conservative replication’?

A

this refers to the fact that when the DNA replicates each new DNA contains one ‘old strand’ from the original molecule and one ‘new stand’ that is the replicated section.

39
Q

describe the process of DNA replication.

A
  • DNA helicase causes the two stands to separate.
  • free nucleotides that have been activated are attracted to their complementary base pairs on each strand.
  • nucleotides are attached by DNA polymerase
  • two molecules have been produced.
40
Q

state the role of DNA polymerase in replication.

A

free nucleotides pair with newly exposed bases on the template strand during the unzipping process. DNA polymerase catalyses the formation of phosphodiester bonds between the nucleotides.

41
Q

state the role of DNA helicase in replication.

A

DNA helicase travels along the backbone, catalysing the reaction that breaks the hydrogen bonds between complementary base pairs as it reaches them.

42
Q

explain Meselson and Stahl’s experiment.

A
  • they used E.coli bacteria raised in N14 then extracted and centrifuged their DNA to find it’s density.
  • they did the same for N15, a heavier isotope.
  • when E.coli was placed in N14 for one generation and N15 for the next the DNA was a density in between the two. proving semi conservative replication.
43
Q

explain how one strand of DNA goes through continuous replication but the other goes through discontinuous replication.

A

DNA polymerase can only bind to the 3’ end of the DNA strand and unzip up in that direction. this strand can continuously replicate as it unzips. this is continuous replication and is known as the leading strand. however the strands are antiparallel so the other strand cannot. instead it replicates in short strands called Okasaki fragments. these are then joined together by the enzyme DNA ligase. this is discontinuous replication and is known as the lagging strand.

44
Q

why is it important to replicate DNA accurately?

A

any changes to the DNA sequence can lead to mutations.

45
Q

what is a mutation?

A

a change in the sequence of bases in DNA.

46
Q

how can the bases in DNA code for the primary structure of a polypeptide chain?

A

DNA codes for a sequence of amino acids. each codon (set of three bases) codes for a specific amino acid.

47
Q

define the term codon.

A

a sequence of three bases that codes for an amino acid.

48
Q

define the term gene.

A

a section of DNA that contains the complete sequence of bases to code for an entire protein.

49
Q

define the term triplet code.

A

each triplet/set of three bases codes for a particular amino acid.

50
Q

define the term non-overlapping.

A

the genetic code has a start codon - methionine which means the base is read from 1 onwards - the triplets are clear.

51
Q

define the term degenerate.

A

different combinations of bases can code for the same amino acid.

52
Q

define the term universal.

A

all organisms use the same code, although the sequence of bases will be different.

53
Q

define the term start codon.

A

methionine is the start codon for all proteins. it signals the start of a new gene.

54
Q

define the term stop codon.

A

a codon that does not code for any amino acid and signals the end of a gene.

55
Q

define the term transcription.

A

the creation of a single stranded mRNA copy of the DNA coding strand.

56
Q

define the term translation.

A

the process where polypeptides are assembled at ribosomes from a strand of transcribed RNA.

57
Q

state the three types of RNA.

A

tRNA
mRNA
rRNA

58
Q

compare the structure and function of tRNA and mRNA.

A

mRNA is a straight, single stranded chain of RNA synthesized my a gene containing information on protein synthesis. it acts as a carrier from nucleus to ribosomes.
tRNA is also single stranded but has loops which make some sections double stranded. tRNA is used to transfer amino acids by instructions given by mRNA. each tRNA molecule carries a different amino acid.

59
Q

describe the process of transcription.

A
  • DNA helicase unzips the two strands by breaking the hydrogen bonds between base pairs.
  • this exposes the bases along each strand
  • free RNA nucleotides with the bases A,C,G and U are attracted to their complementary base pair on the exposed strands.
  • the enzyme DNA polymerase moves along the DNA, adding one complementary RNA nucleotide at a time to the newly unwound portion of DNA; in this way the DNA acts as a template against which mRNA is constructed.
  • the mRNA detaches from the DNA and the double helix reforms its double helix.
  • the mRNA enters the cytoplasm by passing through a pore in the nuclear envelope.
60
Q

define the term sense strand

A

the strand of DNA that contains the instructions to make a protein. it is not used as a template during transcription as it is the strand that needs to be replicated.

61
Q

define the term antisense strand.

A

the complementary strand of the sense strand that doesn’t code for a protein and does act as a template

62
Q

define the term template strand.

A

another word for the antisense strand, it acts as a template as RNA nucleotides that bond to it will be a copy of the sense strand.

63
Q

describe the structure of a ribosome.

A

has two parts, with a kind of slot in the middle, made of rRNA which makes up 80% of RNA in cells.

64
Q

describe the role of rRNA.

A

important in maintaining the structural stability of the protein synthesis sequence and plays a role in catalysing the reactions.

65
Q

describe the process of translation.

A
  • a ribosome becomes attached to the mRNA
  • the complementary anticodon of the tRNA is attracted to the first codon on the mRNA.
  • hydrogen bonds form between the codon and the anticodon
  • a peptide bond forms between the two amino acids
  • a dipeptide is formed
  • the first tRNA leaved the ribosome to join with another molecule of it’s specific amino acid.
  • the ribosome moves along the mRNA by one codon.
    a third tRNA brings its specific amino acid to the ribosome
  • this process is repeated to build up a polypeptide chain
  • the ribosome continues along the mRNA until it reaches the stop codon.

biology (22 decks)

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