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AQA A Level Biology Paper 1 > Topic 4.1 - The Genetic Code and Protein Synthesis > Flashcards

Topic 4.1 - The Genetic Code and Protein Synthesis Flashcards

Includes DNA, genes and chromosomes, and transcription and translation.

1
Q

What is the basic function of DNA?

A

Used to store genetic information

(all instructions organism needs to grow and develop from fertilised egg to adult)

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2
Q

What is the main function of RNA?

A

Transfer genetic information from DNA to ribosomes

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3
Q

What do ribosomes do?

A

Read RNA to make polypeptides in process called translation

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4
Q

What are ribosomes made from?

A

RNA and proteins

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5
Q

What 3 things does a nucleotide consist of?

A
  • Nitrogen-containing organic base
  • Pentose sugar
  • Phosphate group
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6
Q

What are monomers that make up DNA & RNA?

A

Nucleotides

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7
Q

How are polynucleotides formed?

A
  • Nucleotides join via condensation reaction between phosphate group of one nucleotide and sugar of another
  • This forms a phosphodiester bond
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8
Q

What is a chain of sugar and phosphates called?

A

Sugar-phosphate backbone

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9
Q

What is the pentose sugar in a DNA nucleotide?

A

Deoxyribose

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10
Q

Each DNA nucleotide has same sugar & phosphate group but a different…

A

nitrogen base

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11
Q

Name the 4 possible bases in a DNA nucleotide

A
  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)
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12
Q

What is the pentose sugar in a RNA nucleotide?

A

Ribose

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13
Q

Name the 4 possible bases in a RNA nucleotide

A
  • Adenine (A)
  • Uracil (U)
  • Cytosine (C)
  • Guanine (G)
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14
Q

Describe how the structure of DNA is formed

A
  1. 2 DNA polynucleotide strands join together by hydrogen bonding between complementary base pairs
  2. 2 hydrogen bonds form between A & T, and 3 hydrogen bonds form between C & G
  3. 2 antiparallel polynucleotide strands twist to form DNA double-helix
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15
Q

What does adenine pair with?

A

Thymine (A - T)

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16
Q

What does cytosine pair with?

A

guanine (C - G)

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17
Q

There is always _____ amounts of A & T in DNA molecule and C & G

A

EQUAL

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18
Q

Describe the structure of RNA

A

Made from single polynucleotide chain = much shorter than most DNA polynucleotides

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19
Q

Name 3 Types of RNA in every cell

A
  • tRNA
  • rRNA
  • mRNA
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20
Q

What does rRNA do?

A

Type of RNA that makes up ribosomes

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21
Q

Explain how the structure of DNA is related to its functions (6)

A
  1. Double helix protects bases from corruption
  2. Large molecule so can store lots of genetic information
  3. Helix/coiled so compact
  4. Double stranded so replication can occur semi-conservatively
  5. (Weak) H-bonds for replication
  6. Many H-bonds so stable
  7. Complementary base pairing so accurate identical copies can be made
  8. Base sequence allows information to be stored
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22
Q

Explain why the replication of DNA is described as semi-conservative (2)

A
  • Each strand copied / acts as a template
  • DNA has one new strand & one orginial
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23
Q

Describe stage 1 of semi-conservative replication

A

DNA helicase breaks H bonds between bases = backbone is unzipped = helix unwinds

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24
Q

Describe stage 2 of semi-conservative replication

A

Each original single strand acts as template for new strand:

Free nucleotides are attached to their complementary base on the backbone (orginal strand)

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25
Q

Describe stage 3 of semi-conservative replication

A
  • Condensation reactions join nucleotides - catalysed by enzyme DNA polymerase
  • H bonds form between bases (on original and new strands)
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26
Q

Describe stage 4 of semi-conservative replication

A

Each new DNA molecule contains one strand from original DNA molecule and one new strand

(Double strand twists again)

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27
Q

What are the differences between eukaryotic DNA and prokaryotic DNA?

A

Nuclear eukaryotic DNA is linear & associated with proteins. Whereas prokaryotic DNA is much shorter and circular, and not associated with proteins.

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28
Q

What is the name of the proteins that DNA associates with?

A

histones

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29
Q

What do histone proteins do?

A

Help support the DNA

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30
Q

DNA molecules and histone are coiled up very tightly to make _____ ________

A

compact chromosomes

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31
Q

What is the DNA in mitochondria and chloroplast (in eukaryotes) like?

A

Similar to prokaryotic DNA because its circular and shorter than DNA in nucleus & it’s not associated with histone proteins

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32
Q

How does prokaryotic DNA fit into cells?

A

Condenses to fit in cell by supercoiling

33
Q

What is a gene?

A

Sequence of DNA bases that codes for either a polypeptide or functional RNA

34
Q

What do different polypeptides have?

A

They have different no. and order of amino acids

35
Q

What determines the order of amino acids in a polypeptide?

A

The order of bases in a gene

36
Q

What is each amino acid coded by?

A

A sequence of 3 bases in gene = called triplet or codon

37
Q

What is meant by a cell’s genome?

A

The complete set of genes in the cell

38
Q

What is meant by a cell’s proteome?

A

Full range of proteins that the cell is able to produce

39
Q

Most DNA in eukaryotic cells _____ code for polypeptides

40
Q

In eukaryotic DNA, genes that code for _______ contain sections that…

A

In eukaryotic DNA, genes that code for polypeptides contain sections that don’t code for amino acids

41
Q

What are introns?

A

Sections of DNA that don’t code for amino acids

42
Q

Can there be several introns within a gene?

43
Q

What are exons?

A

Bits of gene that do code for amino acids

44
Q

When are introns are removed?

A

During transcription

45
Q

Prokaryotic DNA doesn’t have ____

46
Q

What are multiple
tandem repeats?

A

DNA sequences that repeated over and over again

e.g. CCTTCCTTCCTT

47
Q

Multiple repeats ____ code for amino acids & are called ______ ____

A

Multiple repeats don’t code for amino acids & are called non-coding repeats

48
Q

What is meant by the term allele?

A

Order of bases in each alleles is slightly different ∴ they code for slightly different versions of the same polypeptide (genes with the same locus)

49
Q

What is homologous pair?

A

Pair of matching chromosomes: both chromosomes are same size & have same genes (BUT could have different alleles)

50
Q

Where are alleles coding for the same characteristic found on chromsomes in a homologous pair?

A

Found at same fixed position (locus) on each chromosome in a homologous pair

51
Q

Explain why DNA helicase is important in DNA replication (2)

A
  • Breaks H-bonds
  • (So) nucleotides can attach/strands can act as templates
52
Q

Draw 2 nucleotides joining together

53
Q

When is mRNA made?

A

During transcription

54
Q

Describe the structure of mRNA

A

It’s a single polynucleotide strand (& has groups of 3 adjacent bases)

55
Q

What does tRNA do?

A

Carries amino acids that are used to make proteins to ribosomes

(involved in translation)

56
Q

What does mRNA do?

A

Carries genetic code from DNA to ribosomes & is then used to make a protein during translation

57
Q

Describe the structure of tRNA

A

It’s a single polynucleotide strand that’s folded into clover shape

58
Q

How does tRNA stay in a clover shape?

A

H-bonds between specific base pairs hold it in shape

59
Q

What does every tRNA molecule have? (2x)

A
  • Anticodon at one end - specific sequence of 3 bases
  • An amino acid binding site at other end
60
Q

What is the main thing that happens in transcription?

A

mRNA copy of gene is made from DNA

61
Q

In eukaryotic cells, where does transcription takes place?

62
Q

Describe the stages in transcription

A
  1. DNA helicase (in eukaryotes) breaks H-bonds between 2 DNA strands (in beginning of a gene)
  2. Only one DNA strand acts as a template (to make mRNA copy)
  3. Free bases in RNA nucleotides are attracted to exposed bases
  4. Attraction occurs according to complementary base pairing (therefore mRNA strand becomes a complementary copy of DNA template strand)
  5. RNA nucleotides are joined together by RNA polymerase
  6. (In eukaryotes) mRNA moves out through nuclear pore
63
Q

Where does transcription take place in prokaryotes?

64
Q

When does the RNA polymerase stop making mRNA and detachs from DNA in transcription?

A

When RNA polymerase reaches a particular sequence of DNA called stop signal

65
Q

Where does translation occur in both eukaryotes and prokaryotes?

A

At ribosomes in cytoplasm

66
Q

What is the main thing occuring during translation?

A

Amino acids are joined together to make polypeptide chain, following the sequence of codons (triplets) carried by mRNA

67
Q

Describe the stages in translation

A
  1. mRNA moves into cytoplasm & attaches to ribosome
  2. tRNA carry amino acids to it
  3. Specific tRNA molecule for specific amino acid
  4. Anitcodon of tRNA binds to complementary codon on mRNA (attaches by specific base pairing)
  5. Peptide bond forms between amino acids
  6. tRNA detaches and collects another amino acid
  7. Ribosome moves along mRNA = forming a long polypeptide chain
68
Q

What determines how the folded protein structure of protein will be?

A

Position of R groups in polypeptide chain

69
Q

What is the genetic code?

A

Sequence of base triplets (codons) in mRNA which code for specific amino acids

70
Q

Name 3 qualities of the genetic code

A
  1. Non-overlapping
  2. Degenerate
  3. Universal
71
Q

Describe how genetic code is non-overlapping

A

Each base triplet is read in sequence only once

72
Q

Describe how genetic code is degenerate

A

Some amino acids are coded by more than one base triplet

e.g. tyrosine can be coded for by UAU or UAC

73
Q

Describe how genetic code is universal

A

Same specific base triplets code for same amino acids in all living things

e.g. UAU codes for tyrosine in all organisms

74
Q

What are start/stop signals (or codons)?

A

Triplets that tell the cell when to start/stop production of a protein

75
Q

What is pre-mRNA?

A

mRNA strands containing introns and exons

76
Q

Why does pre-mRNA contain introns and exons?

A

Introns and exons are both copied into mRNA during transcription

77
Q

Name and describe the process how pre-mRNA is made into mRNA

A

Process called splicing occurs: introns are removed and exons join together = forming mRNA strands

78
Q

What does transcription make in prokaryotes?

A

mRNA - it’s produced directly from DNA without splicing

AQA A Level Biology Paper 1 (12 decks)

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