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OCR A-Level Biology > Chap 3 - Nucleotides > Flashcards

Chap 3 - Nucleotides Flashcards

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1
Q

State 2 common types of nucleic acid

A

Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)

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2
Q

Compare the different components of RNA and DNA

A

RNA: ribose sugar, nitrogenous base, phosphate group
DNA: deoxyribose sugar, nitrogenous base, phosphate group

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3
Q

Compare the nitrogenous bases of RNA and DNA

A

RNA: uracil, adenine, cytosine, guanine
DNA: thymine, adenine, cytosine, guanine

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4
Q

What are the 2 groups of nitrogenous bases?

A

pyramidines: cytosine, thymine, uracil
purines: guanine, adenine

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5
Q

Describe the structure of the 2 groups of nitrogenous bases

A

pyrimidines - smaller, contain single carbon ring structures
purines - larger, contain double carbon ring structures

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6
Q

Define monomer

A

individual molecules that make up a polymer.

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7
Q

Define polymer

A

long-chain molecules composed of multiple bonded individual molecules (monomers) in a repeating pattern.

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8
Q

Define nucleic acids and name which elements they are composed of

A

large polymers formed from nucleotides
Contain: C, H, N, P, O

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9
Q

Define polynucleotide

A

polymer composed of 13 or more nucleotide monomers covalently bonded in a chain.

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10
Q

Define nucleotide

A

monomers used to form nucleic acids
made up of: a pentose monosaccharide, a phosphate group and a nitrogenous base

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11
Q

Define phosphodiester bond

A

a covalent bond in which a phosphate group joins adjacent carbons through ester linkages

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12
Q

State the name of the reaction that joins nucleotides together

A

condensation reaction

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13
Q

State the name of the reaction that breaks phosphodiester bonds

A

hydrolysis

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14
Q

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

A

synthesis
transport
movement

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15
Q

List 2 similarities and 2 differences between ATP, DNA and RNA nucleotides.

A

similarities:
- all have pentose sugar in the middle
- all contain nitrogenous bases

differences:
- DNA pentose sugar is deoxyribose, ATP and RNA contain ribose
- ATP contains 3 phosphate groups per nucleotide, RNA and DNA contain 1 per nucleotide

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16
Q

State 5 properties of ATP and explain why each makes it ideally suited to function as an energy transfer molecule.

A
  • small - moves easily into/out of and within cells
  • water soluble - energy-requiring processes happen in aqueous env
  • bonds between phosphates with intermediate energy - large enough to be useful for cellular reactions but not so large that energy is wasted as heat
  • releases energy in small quantities - quantities are suitable to most cellular needs so energy is not lost as heat
  • easily regenerated - can be recharged w energy
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17
Q

Define phosphorylation

A

the addition of phosphate to an organic compound.

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18
Q

Define the term complementary base pairing, state the rules and number that holds each pair together.

A

specific hydrogen bonding between nitrogenous bases
- adenine binds to thymine/uracil (2 H bonds)
- cytosine binds to guanine (3 H bonds)

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19
Q

Define sugar-phosphate backbone.

A
  • forms the structural framework of nucleic acids.
  • composed of alternating sugar and phosphate groups, and defines directionality of the molecule.
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20
Q

Define anti-parallel

A

DNA strands that run parallel to each other but with opposite directionality

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21
Q

Define double helix

A

two strands that wind around each other like a twisted ladder

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22
Q

Define DNA strand

A

one of two polynucleotide chains that make up the double helix structure

23
Q

Explain why a DNA molecule has equal amounts of adenine and thymine and equal amounts of cytosine and guanine.

A
  • DNA is double-stranded and has complementary base pairing
  • therefore means that for every nitrogenous base there will be an equal amount of its complementary base pair present on the opposite strand
24
Q

Describe the significance of the double-stranded, complementary base paired nature of DNA for its function.

A
  • allows it to be copied and transcribed
  • this means the very large DNA molecule does not need to leave the nucleus in order for a cell to receive info for protein synthesis
25
Q

Describe the significance of the sequence of bases in a DNA strand for its function.

A
  • the sequence carries the genetic info of an organism
  • 3 consecutive bases code for a single amino acid
26
Q

Explain why DNA replication is necessary

A
  • DNA replication is necessary for a cell to divide (mitosis/meiosis)
27
Q

Define semi-conservative replication.

A

DNA replication results in one old strand and one new strand present in each daughter DNA molecule

28
Q

Describe the process of DNA replication

A
  • DNA helicase causes two strands of DNA to separate
  • free nucleotides that have been activated are attracted to their complementary bases
  • when nucleotides are lined up, they are joined together by DNA polymerase.
  • remaining unpaired bases continue to attract complementary nucleotides.
  • all nucleotides are joined to form a complete polynucleotide chain using DNA polymerase.
  • two identical DNA molecules are formed, each is composed of one original strand and one newly formed molecule
29
Q

State the roles of DNA polymerase and DNA helicase in DNA replication.

A
  • DNA polymerase - joins nucleotides together to form a polymer
  • DNA helicase - breaks hydrogen bonds between complementary base pairs causing the two strands to separate
30
Q

Explain the importance of DNA replication conserving genetic information with accuracy.

A
  • new cells receive an exact copy of the organism’s genetic sequence when dividing
  • less chance of mutations occuring
31
Q

Define mutation

A

a change in the base sequence of DNA which may affect the phenotype of an organism

32
Q

Outline how the sequence of bases in DNA can code for the primary structure of a polypeptide chain.

A
  • a sequence of 3 base pairs will code for one amino acid
  • the base pair sequence will determine the order of amino acids in protein synthesis
  • therefore determines the primary structure of a polypeptide
33
Q

Define codon

A

a three-base sequence of DNA/RNA that codes for an amino acid

34
Q

Define gene

A

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

35
Q

Define triplet code

A

describes that the genetic code is a sequence of three nucleic acid bases (codons)

36
Q

Define non-overlapping

A
  • each codon is read separately from the codon before it and the codon after it.
  • no base is shared between adjacent codons
37
Q

Define degenerate code

A

describes how there are 20 diff amino acids but 64 possible codons so many amino acids can be coded for by more than one codon

38
Q

Define universal code

A

refers to the the fact that the same specific codons code for the same amino acids in all living organisms

39
Q

Explain why the genetic code is a triplet code

A
  • a sequence of 3 bases codes for 1 amino acid
  • if it was a doublet code, there would be 16 possible codons - not enough for 20 amino acids
  • 64 possible codons - allows multiple codons to code for a single amino acid, reducing the effects of mutations on protein structure
40
Q

Explain the value of the genetic code being non-overlapping

A
  • each subsequent codon is not limited to the last 2 letters of the codon before
  • this means there can be any combination of amino acids
41
Q

Explain why the genetic code is degenerate

A
  • for most amino acids there is more than 1 possible codon
  • not all mutations will change the amino acid sequence & primary structure
42
Q

Describe what is meant by a start codon and a stop codon.

A
  • start codon marks the site at which translation into protein sequence begins (AUG, codes for methionine)
  • stop codon marks the site at which translation ends (UGA, UAA, UAG, do not code for an amino acid)
43
Q

Outline how mutations can alter the structure of a protein.

A
  • a mutation occurs randomly in a gene
  • base sequence is changed so that the wrong amino acid is coded for in the protein
  • primary structure is changed so the tertiary structure is altered and the function may be lost
44
Q

Define transcription

A

the process of copying sections of DNA base sequence to produce smaller molecules of mRNA which can be transported out of the nucleus via the nuclear pores to the site of protein synthesis.

45
Q

Define translation

A
  • the process by which the complementary code carried by mRNA is decoded by tRNA into a sequence of amino acids.
  • occurs at a ribosome
46
Q

Name the 3 types of RNA

A

tRNA - transfer RNA
mRNA - messenger RNA
rRNA - ribosomal RNA

47
Q

Compare the structure of the 3 types of RNA

A

mRNA: linear, single stranded molecule, contains ribose, contains bases A, U, G, C, carries codon sequence complementary to the sequence of the gene

tRNA: single strand of RNA folded into clover leaf shape with three bases (anticodon) at one end of molecule, contains ribose, contains bases A, U, G, C, carries an anticodon which is complementary to the codon on mRNA

rRNA: double-stranded, antiparallel double helix molecule, contains deoxyribose, contains bases A, T, G, C, carries the original codon complementary to mRNA

48
Q

Compare the function of the 3 types of RNA

A

mRNA: carries genetic information (amino acid sequence order) copied from DNA

tRNA: delivers correct amino acids to the ribosome in order to make up a polypeptide

rRNA: carries the genetic material of an organism

49
Q

Describe the process of transcription

A
  • section of DNA that contains the gene is unwound by DNA helicase at the start of the gene
  • RNA polymerase adds the free complementary ribonucleotides to the template (antisense) strand
  • sense strand of DNA contains the triplet code in correct order but is not transcribed
  • anti-sense strand of DNA is complementary to the sense strand and is transcribed to make mRNA which is a copy of the sense strand
  • ribonucleotides are joined together by condensation (phosphodiester bonds) to form a copy of the gene in the form of mRNA
  • when the whole gene was transcribed, mRNA separates from DNA and leaves the nucleus through the nuclear pores
50
Q

Describe the process of translation

A
  • mRNA binds to small subunit of ribosome at its start codon
  • A tRNA with the complementary anticodon binds to the mRNA start codon (tRNA carries the corresponding amino acid)
  • next tRNA with anticodon, carrying the corresponding amino acid, binds to the next codon on mRNA
  • maximum of two tRNA can be bound at same time
  • first amino acid is bound to the second tRNA amino acid by the formation of a peptide bond - catalysed by peptidyl transferase
  • ribosome moves along mRNA releasing the first tRNA, the second tRNA becomes the first until the stop codon is reached, leaving fully assembled polypeptide chain
51
Q

Define sense strand

A

strand of DNA that runs 5’ to 3’ and contains the genetic code for a protein.

52
Q

Define anti-sense strand

A
  • strand of DNA that runs 3’ to 5’ and is complementary to the sense strand.
  • acts as a template strand during transcription
53
Q

Define template strand

A

antisense strand of DNA that acts as a template during transcription so that the complementary mRNA strand formed carries the same code for a protein as the DNA sense strand

54
Q

Describe the structure of a ribosome and explain the role of rRNA.

A
  • ribosomes are made up of a large and a small subunit
    rRNA is what makes up the ribosome (structural role)

OCR A-Level Biology (16 decks)

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