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Biology > 4A DNA, Genes and Protein Synthesis > Flashcards

4A DNA, Genes and Protein Synthesis Flashcards

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1
Q

How do prokaryotes and eukaryotes store DNA differently?

A
  • eukaryotic cells contain linear DNA
  • prokaryotes contain circular DNA
  • DNA in eukaryotes exist as chromosomes that are thread-like structures made of DNA and histone proteins found in the nucleus of cells
  • in prokaryotes DNA is free-floating and not bound to histones, it fits into the cell by super-coiling
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2
Q

What organelles have their own DNA?

A
  • mitochondria and chloroplasts
  • it is similar to prokaryotic DNA
  • circular and not bound to histones
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3
Q

What is a gene?

A

A region of DNA that codes for a protein

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4
Q

What does the order of bases in DNA determine?

A

The order of amino acids in a protein

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5
Q

What is one amino acid coded by?

A

3 bases/ codon

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6
Q

Other than amino acids for a protein, what may a gene code for?

A
  • a section of functional RNA
  • eg. transfer RNA or ribosomal RNA
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7
Q

What are genomes?

A

Collection of organism’s genes

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8
Q

What are proteomes?

A

Collection of organism’s proteins

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9
Q

What are non-coding regions of DNA?

A
  • DNA in eukaryotes that doesn’t code for a protein
  • introns
  • removed during protein synthesis
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10
Q

Does prokaryotic DNA have introns and/or exons?

A

No, just exons

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11
Q

What are microsatellites/short tandem repeats?

A
  • eukaryotic DNA contains repeating regions of DNA located outside of genes
  • these regions are non-coding
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12
Q

What are alleles?

A
  • multiple forms of genes
  • humans usually have 2 alleles of the same gene, one on each chromosome
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13
Q

What can alleles lead to?

A
  • may lead to slightly different proteins being made
  • eg . different alleles for eye colour may produce blue and brown proteins
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14
Q

How many chromosomes do humans have in each cell?

A
  • 23 homologous pairs
  • 2 copies of the same chromosome in each human cell (one maternal and one paternal)
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15
Q

What is a homologous pair?

A
  • when 2 chromosomes that are the same size and contain the same genes arrange themselves in a homologous pair
  • they may have different alleles
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16
Q

What is a karyotype?

A
  • how chromosomes are displayed
  • a visual illustration of an organism’s collection of chromosomes
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17
Q

What enzyme unravels DNA double helix to a straight ladder?

A

Gyrase

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18
Q

What is the function of DNA helicase?

A
  • separates 2 strands of DNA for replication
  • it catalyses the disruption of the hydrogen bonds holding the 2 strands together
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19
Q

What is the function of RNA polymerase?

A
  • copies a DNA sequence into a RNA sequence
  • links the nucleotides of the new RNA strand in transcription
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20
Q

Where in the cell does transcription occur?

A

Nucleus

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21
Q

Describe the unwinding of DNA during transcription

A
  • first step of transcription
  • DNA unwinds and hydrogen bonds break between complementary bases
  • gene is now exposed to be replicated
  • complementary copy of the code from the gene is made by building a single-stranded nucleic acid molecule (mRNA)
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22
Q

How is RNA polymerase involved in transcription?

A
  • moves along template strand of DNA
  • adds complementary bases to template strand and joins them with phosphodiester bonds
  • stops transcribing when it reaches a stop codon
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23
Q

Describe the coding strand involved in transcription

A
  • it is the opposite strand of DNA to the template strand
  • the base sequence is identical to the sequence in the new mRNA strand (except it has thymine instead of uracil)
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24
Q

How does the double-stranded DNA molecule reform?

A
  • when the gene has been transcribed the hydrogen bonds between mRNA and DNA break
  • hydrogen bonds reform between 2 DNA strands (template and coding)
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25
Q

Where does translation occur in the cell?

A
  • in the cytoplasm
  • mRNA attaches to a ribosome
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26
Q

Describe how anticodons are involved with translation

A
  • free molecules of tRNA in cytoplasm have a triplet of unpaired bases at one end called an anticodon
  • this is a region where they can bind to codons in mRNA
  • they pair with their complimentary codon in the mRNA
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27
Q

Describe how tRNA is involved in translation

A
  • there are at least 20 tRNA molecules each with different anticodons and amino acids
  • tRNA molecules bind with their specific amino acid in the cytoplasm and bring them to the mRNA on the ribosome
  • 2 molecules of tRNA fit on the ribosome at any one time and a peptide bond is formed between the 2 amino acids
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28
Q

What is required for the joining of amino acids during translation?

A
  • ATP
  • provided by mitochondria
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29
Q

When does translation end?

A
  • when a stop codon is reached
  • amino acid chain forms final polypeptide
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30
Q

How are proteins made?

A
  • made during protein synthesis
  • 2 main stages, transcription and translation
  • transcription: DNA transcribed into a molecule of messenger RNA
  • translation: mRNA is translated into a protein at a ribosome
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31
Q

Describe eukaryotic RNA

A
  • single-stranded molecule
  • contains nucleobase uracil rather than thymine
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32
Q

How is mRNA made?

A
  • during transcription
  • synthesised using a DNA template
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33
Q

What is an mRNA codon?

A
  • a 3 base sequence
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34
Q

Why is tRNA important during translation?

A
  • carries amino acids from cytoplasm to ribosome
  • amino acids are used to assemble protein
  • it is a single polynucleotide folded to resemble 3 leaf clover shape
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35
Q

What is included in pre-mRNA that isn’t in mRNA?

A
  • introns
  • regions that don’t code for a protein
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36
Q

What is splicing and describe the process

A
  • introns are removed from pre-mRNA during splicing
  • splicing removes introns and the exons are spliced together
  • mRNA is then mature mRNA and it leaves the nucleus to associate with a ribosome
37
Q

Does prokaryotic DNA have introns and exons?

A
  • just exons
  • no non-coding regions
  • there is no mechanism for splicing in prokaryotes
38
Q

Describe purines and pyramidines

A
  • adenine and guanine are purine
  • cytosine and thymine/uracil are pyramidine
39
Q

What is the sugar involved in DNA, mRNA and tRNA?

A
  • DNA: deoxyribose
  • mRNA: ribose
  • tRNA: ribose
40
Q

Are histones involved in DNA, mRNA and tRNA?

A
  • DNA: yes in euks no in proks
  • mRNA: no
  • tRNA: no
41
Q

What are the nucleotides involved in DNA, mRNA and tRNA?

A
  • DNA: ATCG
  • mRNA: AUCG
  • tRNA: AUCG
42
Q

What is the shape involved in DNA, mRNA and tRNA?

A
  • DNA: double helix
  • mRNA: single linear strand
  • tRNA: 3 leaf clover
43
Q

What is the size of DNA, mRNA and tRNA?

A
  • DNA: big
  • mRNA: small
  • tRNA: smaller
44
Q

Describe tRNA structure

A
  • made up of 76 bases always
  • all the same in every tRNA molecule except the anticodon
45
Q

What is the genetic code?

A
  • the means by which DNA and RNA molecules carry genetic information in cells
  • it is a sequence of triplet codons that code for specific amino acids
46
Q

Describe how the genetic code is non-overlapping

A
  • same base is not used for 2 different codons/triplets
  • no base can take part in the coding of two or more amino acids
47
Q

Describe how the genetic code is degenerate

A
  • there is more possible combos of triplet codons than there are amino acids
  • there’s 64 codons but only 20 amino acids
  • this means more than one codon codes for the same amino acid
  • 3 stop codons can signal the ribosome to cease protein production
48
Q

Describe how the genetic code is universal

A
  • all living things have the same codons coding for the same amino acids
  • eg. codon GAC codes for aspartic acid in all organisms
49
Q

Describe the genetic code with 3 terms

A
  • non-overlapping
  • degenerate
  • universal
50
Q

What is a mutation?

A
  • a change in the DNA base sequence
  • gene mutations occur in regions of DNA that code for a protein
51
Q

What is a substitution mutation?

A
  • occurs when one base is substituted for another
52
Q

What is a deletion mutation?

A
  • occurs when one base is completely removed
53
Q

What is a deletion mutation?

A
  • occurs when one base is completely removed
54
Q

What is an insertion mutation?

A
  • occurs when 1 base is inserted
55
Q

What is an inversion mutation?

A
  • occurs when a section of bases is reversed
56
Q

How can mutations change the structure of proteins?

A
  • the order of amino acids in a protein is determined by the sequence of bases in the DNA
  • mutations alter the sequence of bases so structure is changed
57
Q

What is a silent mutation?

A
  • if a substitution mutation occurs but the codon still codes for the same amino acid
  • has no result on the final polypeptide chain
58
Q

Describe a frame shift

A
  • when 1 base is deleted the entire reading frame will shift
  • results in an entirely new sequence of amino acids
  • this can cause many severe genetic diseases eg. cystic fibrosis
59
Q

How do mutations occur?

A

randomly

60
Q

What can increase rate the rate of mutations?

A
  • mutagens
  • they may induce errors in DNA replication or they may damage DNA directly
  • radiation causes direct damage to DNA
  • certain chemicals and viruses can also increase the rate of mutation
61
Q

Describe how radiation can increase the rate of mutation

A
  • UV and other ionising radiation can disrupt bonds in DNA
62
Q

Describe how certain chemicals and viruses can increase the rate of mutation

A
  • cyclophosphamide is a common chemotherapy agent that induces mutation in cancer cells
  • rous sarcoma virus is linked to increased rates of mutation
63
Q

Describe how UV radiation can damage cells

A
  • through the formation of thymine dimers
  • this changes the structure of the double helix and can lead to errors when the DNA comes to replicate
64
Q

What is rous sarcoma virus linked to?

A
  • Ewing’s sarcoma
  • this is a cancer affecting bones and soft tissue
65
Q

What may occur if there is an error during meiosis?

A
  • cells may end up with a different number of chromosomes
  • this is a chromosome mutation
  • some cells may have no copies of a particular chromosome
  • other cells may have 2 or more copies of a particular chromosome
66
Q

Describe what nondisjunction is

A
  • where chromosomes don’t separate correctly
67
Q

What is an example of nondisjunction?

A
  • Down’s syndrome
  • during meiosis one gamete received 2 copies of a chromosome rather than a single copy
  • when fertilisation occurs, the zygote will have 3 copies of one chromosome (chromosome 21 in particular)
68
Q

What are diploid cells?

A
  • cells that have 2 copies of each chromosome
  • one inherited from the mother and one from the father
  • matching copies of chromosomes are homologous
69
Q

What are alleles?

A
  • different versions of each gene
70
Q

What kind of cells are sperm and egg?

A
  • haploid cells
  • they contain one copy of each chromosome rather than 2
71
Q

Describe meiosis briefly

A
  • type of cell division
  • takes place in reproductive organs
  • events during meiosis cause genetic variation
72
Q

Give the name of the single diploid cells in mammals, females and males

A
  • mammals: gametocytes
  • females: oocytes
  • males: spermatocytes
73
Q

What is the result of meiosis?

A
  • 4 haploid daughter cells that are genetically unique
  • these are the gametes
74
Q

What happens in prophase 1 of meiosis?

A
  • chromatin condenses into visible chromosomes and nuclear membrane breaks down
  • crossing over occurs at the chiasmata
75
Q

What happens in metaphase 1 of meiosis?

A
  • pairs of homologous chromosomes line up in a double line at the equator of the cell
  • spindle fibres attach
76
Q

What happens in anaphase 1 of meiosis?

A
  • spindle fibres pull homologous chromosomes to poles of cell and cytokinesis begins
77
Q

What happens in telophase 1 of meiosis?

A
  • nuclear membranes reform and cytoplasm completely divides forming 2 new cells
78
Q

What happens in prophase 2 of meiosis?

A
  • chromosomes condense for second division
  • nuclear membrane breaks down
79
Q

What happens in metaphase 2 of meiosis?

A
  • chromosomes line up at the equator of the cell in a single file line
  • spindle fibres attach to centromeres
80
Q

What happens in anaphase 2 of meiosis?

A
  • spindle fibres pull chromatids away to the poles (centromeres split)
  • cytokinesis starts and nuclear membranes begin to reform
81
Q

What happens in telophase 2 of meiosis?

A
  • chromosomes decondense into chromatin threads wrapped around histones
  • nuclear membranes have fully reformed
82
Q

What are the 2 ways that genetic variation can occur?

A
  • crossing over
  • independent segregation
83
Q

Describe crossing over of chromatids

A
  • during prophase 1 homologous chromosomes come together to form chiasmata
  • sections of chromatids are exchanged with one another
  • this creates a new combination of alleles
84
Q

What is the result of crossing over called?

A

A recombinant chromosome

85
Q

Describe independent segregation

A
  • each homologous pair of chromosomes consists of one maternal and one paternal
  • when homologous pairs are separated during anaphase 1 it’s random which chromosome ends up in which daughter cell
86
Q

Describe the parasitic protist Plasmodium falciparum

A
  • organism that is responsible for malaria
  • only the zygote is diploid, all other cells are haploid
87
Q

How is meiosis related to Plasmodium falciparum?

A
  • occurs when the zygote divides to form sporozoites
  • these affect the salivary glands of the mosquito and are injected into the host when the mosquito has its next blood meal
88
Q

How is mitosis related to Plasmodium falciparum?

A
  • sporozoites divide by mitosis into haploid merozoites in mammals’ liver
  • merozoites divide by mitosis into haploid gametocytes in red blood cells
  • another mosquito will feed on the host and ingest the gametocytes

Biology (17 decks)

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