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A2 Biology > F215: Cellular Control > Flashcards

F215: Cellular Control Flashcards

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0
Q

What is a polypeptide?

A

A polymer consisting of a chain of amino acid residues joined by peptide bonds.

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1
Q

What is a gene?

A

A length of DNA that codes for one or more polypeptides.

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2
Q

What is a genome?

A

The entire DNA sequence of that organism.

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3
Q

What is a protein?

A

A large polypeptide. Some have a single polypeptide chain and some have numerous.

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4
Q

What is a gene locus?

A

Where the gene is located in the chromosome.

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5
Q

What is a genetic code?

A

The sequence of nucleotide bases on a gene.

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6
Q

Describe the genetic code.

A

A triplet code. 3 nucleotide bases code for an amino acid.

A degenerate code, all amino acids have more than one code.

Some codes indicate a stop to the polypeptide chain rather than an amino acid.

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7
Q

What is transcription?

A

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

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8
Q

How does transcription occur?

A

One strand (template strand) of the length Of DNA is used as a template.
Hydrogen bonds between complementary base pairs break.
RNA nucleotides bind to the exposed bases with hydrogen bonds.
Bond joining is catalysed by RNA polymerase.
Two extra phosphates are released.
The mRNA produced is complementary to the base sequence on the coding strand.
The mRNA is passed through a pore in the nuclear envelope to a ribosome.

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9
Q

What is translation?

A

The assembly of polypeptides at ribosomes.

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10
Q

Why is the sequence of amino acids in a protein critical?

A

It forms the primary structure, which also determines the tertiary structure.
The tertiary structure determines the functioning of a protein. If it is altered the protein no longer functions.

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11
Q

Describe an anticodon.

A 
On tRNA (transfer).
There are three exposed bases at one end whee an amino acid can bind.
Each anticodon can bind temporarily with it's complementary codon.
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12
Q

How is the polypeptide assembled?

A

A molecules of mRNA binds to a ribosome,

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13
Q

What is a mutation?

A

A change in the amount or arrangement of the genetic material in a cell.

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14
Q

What is a chromosome mutation?

A

Changes to parts of or whole chromosomes

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15
Q

What are DNA mutations?

A

Changes to genes due to changes in nucleotide base sequences.

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16
Q

What are the two main classes of DNA mutations?

A

Point mutations/substitutions - where one base pair replaces another.

Insertion/deletion mutations - one or more nucleotide pairs are inserted or deleted from a length of DNA. These cause a frame shift.

Point mutations have a lesser effect since they do not cause a frame shift.

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17
Q

What is an allele?

A

An alternative version of a gene, it is still at the same locus and codes for the same polypeptide but the alteration to the DNA base sequence may alter the proteins structure.

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18
Q

How can mutations have no effect on the organism?

A

If the mutation is in a non coding region of the DNA.

It is a silent mutation, if the changed triplet still codes for the same amino acid.

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19
Q

How is a mutation neutral?

A

If there is a mutation an causes a change that us not her advantageous or disadvantageous.

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20
Q

What is an operon?

A

A length of DNA made up of structural genes and control sites. The structural genes code for proteins, such as enzymes. The control sites are the operator region and a promoter region.

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21
Q

What do the operator and promoter have in common?

A

Both genes since they are lengths of DNA but do not code for polypeptides.

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22
Q

Describe how E. coli adapts depending on it’s environment - glucose and lactose.

A

If taken from a culture with no lactose and placed into one with lactose, they cannot metabolise it at first.
They need beta galactosidase and lactose permease.
After a few minutes these enzymes are made, lactose is thus the inducer.

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23
Q

What two enzymes does E. coli need to respire lactose.

A

Beta galactosidase - catalysed the hydrolysis of lactose to glucose.
Z

Lactose permease - transports lactose into the cell.
Y

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24
Q

What are the sections of the lac operon and their functions?

A

The structural genes:
Z codes for beta galactosidase,
Y codes for lactose permease.

Control sites:
Operator region: O is a length of DNA next to the structural genes, which can switch them on and off.

Promoter region: P is a length of DNA to which the enzyme RNA polymerase binds to begin to the transcription of the structural genes Z and Y.

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25
Q

Where is the regulator gene situated?

A

Not part of the operon, far from the lac operon.

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26
Q

What happens when lactose is absent from the growth medium?

A

The regulator gene is expressed (transcribed & translated) and the repressive protein is synthesised.

It has two binding sites, one to lactose and one to the operator region.

The repressor protein binds to the operator region, and covers part of the promoter region, where RNA polymerase usually attaches.

RNA polymerase cannot attach to the promoter region so the structural genes cannot be transcribed into mRNA.

Without mRNA the genes cannot be translated and the enzymes beta galactosidase and lactose permease cannot be synthesised.

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27
Q

What is a repressor protein?

A

Protein that can bind to the operator region, and RNA polymerase binds to the promoter region to transcribe the structural genes.

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28
Q

What happens when lactose I added to the growth medium?

A

Lactose molecules (inducer) bind to the other site on the repressor protein. Causing the molecules of repressor protein to change shape so it’s other binding site cannot bind to the operator region, the repressor then dissociates from the operator region.

This leaves the promoter region unblocked, and RNA polymerase can bind to it and initiate the transcription of mRNA for Z and Y.

E. coli can then respire using lactose.
The operator-repressor-inducer system is effectively a molecular switch.

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29
Q

What are Hemeobox genes?

A

Genes that control the development of the body plan of an organism, including the polarity (head tail ends) and positioning of the organs.

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30
Q

How are home oboe genes arranged?

A

Into clusters known as hox clusters.

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31
Q

What is a morphogen?

A

A substance that governs the pattern of tissue development by activating the homeobox genes.

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32
Q

What are maternal effect genes and segmentation genes?

A

Maternal effect: determine the embryos polarity.

Segmentation: they specify the polarity of each body segment.

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33
Q

Why should pregnant woman not eat liver?

A

High in vitamin A which contains retinoic acid.
Retinoic acid activates homeobox genes.
It is a morphogen, too much retinoic acid interferes with the expression of the genes.

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34
Q

What is the fly that was studied for it’s hox genes?

A

Drosophila melanogaster.

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35
Q

What is apoptosis?

A

Programmed cell death that occurs in multicellular organisms.

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36
Q

What is apoptosis in contrast with?

A

Necrosis, which is an untidy and damaging cell death that occurs post trauma and released hydrolytic enzymes.

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37
Q

Describe the sequence of events in apoptosis.

A

Quick process.

Enzymes break down the cells cytoskeleton.
The cytoplasm becomes sense, with organisms tightly packed.
The cell surface membrane changes and blebs form.

Chromatin condenses and the nuclear envelope breaks. DNA breaks into fragments.

The cell breaks into vesicles that are taken up by phagocytosis. No hydrolytic enzymes are released.

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38
Q

What is apoptosis controlled by?

A

Cell signals:
Cytokines from immune system
Hormones
Nitric oxide makes the inner mitochondrial membrane more permeable to hydrogen ions and dissipates the proton gradient.

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39
Q

What happens if there is not enough or too much apoptosis?

A

Not enough - tumours forming

Too much - cell loss and degeneration.

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40
Q

Wha is meiosis?

A

A reduction division, the resulting daughter cells have half the original number of chromosomes.
They are haploid and are used for sexual reproduction.

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41
Q

What does haploid mean?

A

They have half the number of chromosomes in each gamete than the original cell.

42
Q

What are gametes?

A

Specialised sex cells.

43
Q

Describe interphase.

A

All the cells DNA is replicated, each chromosome consists of two identical sister chromatids joined at the centromere.
Cell now has four copies of each chromosome as opposed to two.

44
Q

Describe the stages of meiosis.

A

PMAT I & II

45
Q

What is a bivalent?

A

A homologous pair of chromosomes, each consisting of two sister chromatids, paired for meiosis.

46
Q 
Compare meiosis and mitosis.
No of divisions
Products
Chromosome no
Bivalents formed 
Crossing over occurring
A

Mitosis. Meiosis

No of divisions:
One. Two

Products:
Two identical Four different
daughter cells

Chromosome no:
Maintained. Halved

Bivalents:
No. Yes

Crossing over:
No. Yes

47
Q

What is the locus?

A

The position of a gene on a chromosome.

48
Q

What is crossing over?

A

When lengths of DNA are swapped from one chromatid to another.

49
Q

Why is meiosis beneficial?

A

It increases generic variation and encourages random mutations, which increases the chances of evolution as natural selection favours the best adapted.

50
Q

How does meiosis lead to genetic variation?

A

Crossing over shuffles alleles.

Genetic reassignment due to the random distribution of maternal and paternal chromosomes during meiosis I.

Genetic reassortment due to the random distribution and segregation of the sister chromatids at meiosis II.

Random mutation.

51
Q

Describe how crossing over occurs.

A

Prophase I.
The homologous chromosomes pair and come together to form Bivalents.

Non sister chromatids wrap around each other very tightly and attach at the chiasmata.

The chromosomes may break at these points, which then rejoin to ends of the chromatids in the same bivalent.
The sections that swap contain the same genes but different alleles.

Produces new combinations of alleles on the chromatids.

52
Q

Where do chromatids join during crossing over?

A

At the chiasmata.

53
Q

Describe how the reassortment of chromosomes occurs.

A

In metaphase I there is a random distribution of chromosomes on the spindle equator.
Each gamete acquires a different mixture of maternal and paternal chromosomes.

54
Q

Describe how the reassortment of chromatids occurs.

A

Happens in metaphase II.
The chromatids are randomly distributed on the spindle equator.

Because of crossing over the sister chromatids are not identical.

55
Q

What makes alleles co dominant?

A

If they both contribute to the phenotype.

56
Q

What is a genotype?

A

The genetic make up of an organism in terms of the alleles it contains.

57
Q

What type of illness is cystic fibrosis?

A

Homozygous recessive

58
Q

What is a phenotype?

A

The characteristics that are expressed in the organism.

Observable features.

59
Q

Describe the blood types in genetic terms.

A

AB - IA IB
O - IO IO
A - IA IA
IB - IB IB

A and B are codominant.

60
Q

What are the sex linked alleles?

A

XX female

XY male.

61
Q

Describe haemophilia A.

A

Increase in blood clotting time.

Recessive hemizygous, only one allele is needed since males only have one X chromosome, so much more likely to be male.

62
Q

Describe duchenne muscular dystrophy.

A

On the X chromosome.
Muscle weakness, needed for muscle contraction.
Recessive hemizygous. ?

63
Q

Secretive sickle cell anaemia.

A

B strand of haemoglobin differ by one amino acid at position 6.
Normally glutamic acid is there, in sickle valine is present.

When the haemoglobin is then deoxygenated it is insoluble and crystalline, deforming the RBC making them inflexible.

Become lodged in capillaries.

Sickle - HsHs.
Carrier HAHs
Normal HAHA

For carrier the normal haem prevents sickling in RBC.
However both allele contribute to the phenotype in RBCs so it is codominant.

64
Q

What is epistasis?

A

The interaction of different gene loci so that one gene locus masks or suppresses the expression of another gene locus.

65
Q

What are the two types of epistasis?

A

Antagonistic

Complementary

66
Q

Describe recessive epistasis.

A

Where two recessive alleles at one locus mask the other alleles at the other locus.
Eg aaBb. aa is expressed regardless of B or b.

aa is epistatic, B or b is hypostatic.

Antagonistic

67
Q

Describe dominant epistasis.

A

Dominant allele at one locus masks the expression of the alleles at the second locus.

Antagonistic.

68
Q

Describe complementary epistasis.

A

Homozygous recessive alleles at one locus mask the expression of the dominant allele at the other locus.

69
Q 
Describe the ratios of:
Dihybrid cross of unlinked genes
Recessive epistasis
Dominant epistasis
Complementary epistasis
A

Dihybrid cross of unlinked genes
9:3:3:1

Recessive epistasis
9:3:4

Dominant epistasis
12:3:1 or 13:3

Complementary epistasis
9:7

70
Q

What is the chi squared test used for?

A

To find if the difference between observed categorical data and expected data is small enough to be due to chance.

71
Q

What criteria must be met to use the chi squared test?

A

The sample size must be large.
Only raw counts can be used, not ratios or percentages.
There are no zero scores.

72
Q

What is discontinuous variation?

A

Qualitative phenotypic differences, discrete, no intermediate categories.
Eg male/female.

73
Q

What is continuous variation?

A

Quantative phenotypic differences.

Not discrete, eg height or weight.

74
Q

What are myogenic characteristics?

A

Characteristics coded for by one gene.

75
Q

Describe the genetic basis for discontinuous variation.

A

Single different alleles have large effects on the phenotype.
Different loci have a large effect.

76
Q

Describe the genetic basis of continuous variation.

A

Controlled by multiple genes.
Each gene adds to the phenotype, each having a small effect.
Poly genes have a combined effect.

77
Q

What are poly genes?

A

A large number of different genes having a combined effect on the phenotype.

The expression of polygenic traits are influenced more by the environment than the expression of monogenic traits.

78
Q

Why do organisms not always reach their genetic potential?

A

Environmental constraints, eg if not enough nutrition a plant will not grow fully.

79
Q

What is a population?

A

A group of individuals of the same species that can interbreed.

80
Q

What is the gene pool?

A

The set of generic information carried by a population.

81
Q

What is the hardy-Weinberg principle?

A

p^2 + 2pq + q^2 = 1
(p+q) (p+q) = 1

p = dominant allele frequency.
q = recessive allele frequency
q^2 = frequency of all recessive alleles.   cfcf
p^2 = frequency of all dominant alleles.     CFCF 
2pq = frequency of one dominant half dominant half recessive.  CFcf
82
Q

What are chromatin?

A

Uncondensed chromosomes.

83
Q

Describe the first stages of prophase.

A

Prophase I:
Chromatin condenses and undergoes supercoiling so that chromosomes shorten and thicken.

The chromosomes come together in homologous pairs to form Bivalents.
Each has the same genes at the same loci, one maternal/paternal.

Non sister chromatids wrap around each other at the chiasmata.

Crossing over occurs.

Nucleolus disappears and the nuclear envelope disintegrates.

A spindle forms made of protein microtubules.

CSBCSNES

84
Q

Describe metaphase I.

A

Bivalents line up across the equator of the spindle, attached to the centromere (middle).

Bivalents arrange randomly (random assortment) with each member of the homologous pair facing opposite poles.

85
Q

Describe Anaphase I.

A

Apart.
The homologous chromosomes in each bivalent are pulled by the spindle fibres to opposite poles.

Centromeres do not divide.

Chiasmata separate and any crossed over parts remain on the other chromosome.

86
Q

Describe telophase I.

A

Two new nuclear envelopes form, around each set of chromosomes at each pole.

The cell divides by cytokinesis.

Chromosomes uncoil.

87
Q

What is a bivalent?

A

A homologous pair if chromosomes each consisting of 2 sister chromatids paired up for meiosis.

88
Q

What is a dihybrid cross?

A

Two genes independent of each other.

89
Q

What is a selection pressure?

A

An environmental factor confers greater chances of survival to reproductive age on some members of the the population.

90
Q

What is the biological species concept?

A

A group of similar organisms that can interbreed and produce fertile offspring.

91
Q

What is the phylogenetic species concept?

A

A group of organisms that have similar physiology, embryology, behaviour and morphology, and occupy the same ecological niche.

92
Q

What is a monophyletic group?

A

One that includes an ace steal organism and all it’s descendent species.

93
Q

What is cladistics?

A

The hierarchical classification of species, based on evolutionary ancestry.

Focuses on evolution rather than similarities between species.

Uses objective and Quantative analysis

Uses DNA and RNA sequencing.

No distinction between extinct and extant species.

Uses computers to generate diagrams to represent the evolutionary tree of life

94
Q

What is a paraphyletic group?

A

Includes the most recent ancestors but no all it’s descendants.
It is a mono phyletic group with one or more clades excluded.

95
Q

What is a clade?

A

A taxonomic group comprising a single ancestral organism and all it’s descendants.

96
Q

Describe the similarities and differences of natural selection and artificial selection?

A

Similarities:

Both contribute to evolution of the species concerned.

Alters the frequency of alleles.

Differences:

Agent of selection - environment and humans.

Speed - slow and quick

97
Q

Describe a DNA molecule

A

Polynucleotide.
Has a pentose sugar, a phosphate group and a nitrogenous base.
A T C G bases

98
Q

What is a codon?

A

A triplet of bases

99
Q

Why is DNA copied to RNA for protein synthesis?

A

DNA molecules are in the nucleus of a cell, but ribosomes (needed for protein synthesis) are found in the cytoplasm.

DNA is too large to move out of the nucleus so a section is copied to RNA (transcription).

100
Q

Describe RNA.

A

Single polynucleotide strand.
Ribose sugar and uracil base.
Uracil binds to adenine.

RNA joins the ribosome in translation.

mRNA and tRNA

101
Q

Describe mRNA and tRNA.

A

mRNA - made in nucleus.
Codon (three adjacent bases)
Carries code from DNA in nucleus to ribosome in cytoplasm.

tRNA - found in cytoplasm.
Amino acid binding site at one end and anticodon at the other (three bases).
Carries AA to be used to make proteins in the ribosomes in translation.

102
Q

What prevents a population from freely interbreeding?

A

Geographic location.
Seasonal barriers.
Reproductive mechanisms.

A2 Biology (11 decks)

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