Cellular Control and Variation Flashcards
(131 cards)
1
Q
What is the definition of a gene?
A
A length of DNA that codes for one (or more) polypeptide.
2
Q
What is the definition of a chromosome?
A
A thread-like structure of nucleic acids and a protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
3
Q
What is the definition of the genome?
A
The entire DNA sequence of an organism.
4
Q
What is a histone?
A
A protein structure which has been wrapped around by DNA.
5
Q
How are chromosomes formed?
A
DNA and histines combine to form the linear structure.
6
Q
Where is the gene found?
A
On the gene locus on the chromosome.
7
Q
What are the group of bases called on mRNA, tRNA and DNA?
A
DNA- Triplet code
mRNA- Codon
tRNA- Anti-codon
8
Q
How many different amino acids are there?
A
20
9
Q
How many STOP codes are there and name them?
A
3:
UAA
UAG
UGA
10
Q
What does degenerate mean?
A
There are some triplet codes that code for the same amino acid.
11
Q
What is the first step in transcription?
A
The gene that is to be transcribed unwinds and unzips. The length of the DNA molecule that makes up the gene dips into the nucleolus and hydrogen bonds between the bases break.
12
Q
What is the second step in transcription?
A
Activated RNA nucleotides from the nucleolus bind to the exposed DNA bases by hydrogen bonding, following the rules of complementary base pairing. This is catalysed by RNA polymerase.
13
Q
What is the third step in transcription?
A
The two phosphoryl groups on each activated RNA nucleotide are released, which provides energy to form hydrogen bonds between exposed DNA bases and RNA nucleotides.
14
Q
What is the fourth step in transcription?
A
The mRNA molecule produced is complementary to the nucleotide base sequence on the template strand of DNA and is therefore a copy of the coding strand.
15
Q
What is the fifth step in transcription?
A
The mRNA strand is released from the DNA and passes out of the nucleus through a pore in the nuclear envelope.
16
Q
Where are ribosomes synthesised and what from?
A
Synthesised in the nucleolus from ribosomal RNA and proteins.
17
Q
Where is tRNA formed?
A
Nucleus
18
Q
What is tRNA?
A
Single-strand o fRNA that folds into a hairpin shape.
19
Q
What is the importance of cAMP?
A
Activates proteins by changing their 3D shape so that their shape is a better fit to the complementary molecules.
20
Q
What is the first step of translation?
A
A molecule of mRNA binds to a ribosome. The first mRNA codon is always AUG. Using ATP and an enzyme, a tRNA carrying the amino acid methionine and the anticodon UAC forms hydrogen bonds with this codon.
21
Q
What is the second step of translation?
A
A second tRNA, bearing a different amino acid, binds to the second codon with its complementary anticodon.
22
Q
What is the third step of translation?
A
A peptide bond forms between the two adjacent amino acids. An enzyme present in the ribosome catalyses this reaction.
23
Q
What is the fourth step in translation?
A
The ribosome now moves along the mRNA, reading the next codon. A third tRNA brings another amino acid and a peptide bond forms between it and the dipeptide. the first tRNA molecule leaves and is free to collect a new amino acid.
24
Q
What is the final step in translation?
A
The polypeptide chain grows until a stop codon is reached. There are no corresponding tRNA molecules for these drop codon.
25
What is a mutation?
A mutation is a random change to genetic material. There are two main types: DNA and chromosome mutations.
26
What is DNA mutation?
-Causes changes to the order of nucleotides in a `DNA molecule. DNA mutations can be classified as additions, substitutions, inversions, duplications or deletions.
27
What is chromosome mutation?
-Causes changes to the structure of the chromosomes. Chromosome mutations can be classified as inversions, deletions, duplications or translocations.
28
What are the most common types of mutagens?
Gamma radiation
X-ray radiation
Tar
UV radiation
29
What are the conclusions of mutations during mitosis?
- Cannot be inherited by offspring
| - May contribute to ageing or cancer
30
What are the conclusions of mutations during meiosis?
- Can be inherited by offspring
| - Will effect all cells in the individual
31
What are some conditions associated with substitution in DNA mutations?
Cancer and sickle-cell anaemia
32
What are condition/s associated with deletion DNA mutations?
Cystic fibrosis
33
What are condition/s associated with duplication DNA mutation?
Huntington's disease.
34
What is an allele?
An alternative version of a gene, caused by a DNA mutation. The allele has the same gene locus, but eh functioning of the protein may be slightly different.
35
What is missense mutation?
When a mutation change the sequence of amino acids in a polypeptide, which may alter the function of the protein.
36
What is a nonsense mutation?
Mutation alters the amino acid sequence significantly, so the polypeptide cannot be translated, or it becomes shortened (truncated) or elongated. The protein may not function at all.
37
What is a silent mutation?
A mutation does not affect the amino acid sequence in the resulting polypeptide, so the functioning of the protein will be the same.
38
What two sugars is lactose composed of?
Galactose
| Glucose
39
In prokaryotic organisms, enzymes involved in basic cell functions…
Are synthesised at a fairly constant rate.
40
Inducible enzymes are synthesised at varying rates…
According to the cell’s environment.
41
By this form of enzyme induction..
Bacteria can adapt to changing environments and metabolise different substrates when they become abundant.
42
What is the lac operon?
A group of different genes located adjacent to one another on the same chromosome.
It is composed of structural genes and control sites.
43
What do structural genes (regions Y and Z) do?
Code for the enzyme beta-galactosidase(Z) and lactose permease (Y).
44
What does the operator region (Region O) do?
A length of DNA next to the structural genes. It can switch them on and off.
45
What does the promoter region (Region P) do?
A length of DNA to which a molecule of RNA polymerase can bind to.
46
What does the regulator gene (region I) do?
This is not part of the lac operon, but it codes for a repressor molecule.
47
What happens in a lac operon when glucose is present?
A repressor molecule (coded byt he regulatory gene), binds to the operator region.
This prevents RNA polymerase from transcribing the structural genes.
48
What happens in a lac operon when lactose is present?
Lactose acts as an inducer because it binds to the repressor molecule.
This prevents the repressor molecule from binding to the operator region.
As a result. RNA polymerase can bind to the promotor region and is then able to transcribe the structural genes.
49
What do hox genes code for?
The anterior to posterior body plans.
50
What is translation?
Protein synthesis. The sequence of amino acids in the polypeptide chain are determined by the sequence of codons on a messenger RNA molecule.
51
What is a segment?
This is a section of an embryo that will eventually develop into a specific region of the body plan. For instance, some segments produce the head.
52
What is polarity?
This refers to which end of an embryo will develop into the head(anterior portion) or the abdomen (posterior portion).
53
What conclusions can you make about hox genes?
- All animals possess hox genes.
- Occur in the same order on the chromosomes in each animal.
- The order of the hox genes in the chromosomes is the same as the order of embryonic segments in which each box gene is expressed.
54
What are homeobox genes?
They are made up of 180 base pairs.
Code for 60 amino acids.
Known as transcription factors as they attach to other genes further along a chromosome and trigger transcription of these genes.
55
What is apoptosis?
Programmed cell death.
56
What are the steps in apoptosis?
1. Enzymes begin to break down the cell cytoskeleton.
2. The cytoplasm becomes very dense and the organelles become densely packed.
3. The cell surface membrane changed and small bits called blebs form
4. The cell breaks into vesicles that are taken up by phagocytes. This process is called phagocytosis.
57
What is meiosis?
This is a type of nuclear division which produces four daughter cells with the haploid number of chromosomes.
58
What is a homologous chromosomes?
This a pair of chromosomes that are identical in length and contain the same genes at the same loci.
59
What is bivalent?
This is a combination of one pair of paternal chromosomes and one pair of maternal chromosomes.
60
What is a the chiasmata?
These are the points on the chromosome where non-sister chromatids attach to one another.
61
Prophase I
Chromatin condense and chromosomes become visible as they shorten and thicken. A pair of paternal chromosomes forms a bivalent with a pair of maternal chromosomes. Chiasmata form between non-sister chromatids and the nuclear envelope disintegrates. Centrioles move towards poles of the cell.
62
Metaphase I
Bivalents line up along the equator of the cell. they attach to spindle fibres by the centromere.
63
Anaphase I
The centromere divide and chromatids are pulled to opposite poles of the cell.
64
Telophase I
Two nuclear envelopes re-form, one around each set of chromosomes. The cell membrane divides (cytokinesis) to form two diploid cells.
65
Prophase II
If a new nucleus has re-formed, the nuclear envelope will disintegrate one again. Chromosomes shorten and thicken.
66
Metaphase II
The chromosomes arrange themselves along the equator themselves along the equator of the cell. The spindle fibres attach to the centromeres of each chromosome.
67
Anaphase II
The homologous chromosomes in each bivalent are pulled towards the opposite poles of the cell by spindle fibres. The chiasmata separate but the centromeres of not divide.
68
Telophase II
The nuclear envelope reforms around the haploid nuclei. The cell membrane (cytokinesis) will now divide to form four haploid cells.
69
What is the significance of sexual reproduction?
- Sexual reproduction increases genetic variation, as genetic material from cells of of two unrelated organisms combine.
- Genetic variation increases the chances of evolution as natural selection can favour the organisms that possess beneficial mutations.
70
What is the significance of meiosis?
To maintain the original chromosome number, the chromosome number in gametes needs to be halved. Thus, when two haploid gametes join at fertilisation, the resulting zygote is diploid. Therefore meiosis maintains the chromosome number from one generation to the next.
71
What is the definition of allele?
Alternative version of a gene. An allele will produce a slightly different amino acid sequence in the polypeptide.
72
What does it mean by Locus?
This is the position of a gene on a chromosome.
73
What is crossing over?
This is when lengths of DNA are swapped from on chromatid to another.
74
When are mutations most likely to occur?
During S phase of interphase
75
What does it mean by an non-disjunction mutation?
Failure of chromosomes or chromatids to separate.
76
When does crossing over occur?
Prophase I
77
What is the effect of crossing over?
New combination of alleles on the chromatids.
78
What is random assortment?
the reassortment of the maternal and paternal chromosomes on the spindle equator.
79
When does random assortment of chromosomes occur?
Metaphase I
80
When does random assortment of chromatids occur?
Metaphase II
81
What is the theoretical number of different genetically identical gametes that can be created by a human being?
2^n
82
What is it meant by random fertilisation?
- Females produce egg cells that are genetically different.
- Males produce sperm cells that are also genetically different.
- Which sperm fertilises what egg is completely random.
83
What does genotype mean?
Genetic make up of an organism
84
What does phenotype mean?
Characteristics hat are expressed in the organism by the genotype and environment.
85
What is linkage?
Is the tendency of genes that are located close to each other on a chromosome to be inherited together during meiosis. Genes whose loci are nearer to each other are less likely to be separated onto different chromosomes during prophase I, and are therefore said to be genetically linked.
86
What is haemophilia?
Genetic disorder which reduces the ability for blood to clot.
87
What genetic condition is linked with codominance?
Sickle cell anaemia and breeding cows.
88
What type of mutation will cause sickle cell-anaemia?
Substitution of U were A should be on the beta strands of haemoglobin on position 6.
89
Explain why one of the symptoms of sickle-cell anaemia is extreme anaemia?
The shape means less oxygen can diffuse into RBC. Less respiration occurs in organs and muscles.
90
What changes in haemoglobin with someone has SCA?
Normal H- Glutamic acid
| SCA- Valine
91
What happens when he abnormal haemoglobin is deoxygenated?
it is not soluble and becomes crystalline and it changes into more linear and less globular structures. This deforms the shape of the RBC, making them unable to squeeze through capillaries.
92
What is epistasis?
When one gene affects the expression of another.
93
What is recessive epistasis?
The presence of a homozygous recessive allele affects the expression of an allele at a different locus?
94
What is dominant epistasis?
The presence of one dominant allele at one locus affects the expression of an allele at a different locus.
95
What is complementary action?
The presence of an allele at one locus enables the expression of an allele at a second locus.
96
When does complementary action occur?
If one gene codes for a precursor compound and the second gene codes for an intermediate that converts the intermediate compound into the final pigment.
97
Which phenotype ratios are associated with recessive epistasis?
9:3:4
98
Which phenotypes are associated with dominant epistasis?
13: 3
12: 3:1
99
Which phenotypes are associated with complementary action?
9:7
100
What is discontinuous variation?
- Differences in phenotypes fall into discrete categories, with no intermediate phenotypes.
- Qualitative
- Caused by 1 gene (monogenic)
- The allele at one locus have a large effect on the phenotype and different gene loci have very different effects on the phenotype.
101
What is continuous variation?
- Wide range of possible phenotypes, with no discrete categories.
- Quantitive
- Caused by many genes (polygenic)
- Genes at different loci will have an additive effect on the phenotype.
102
Why is variation important in natural selection?
- In environment changes, individuals with advantageous differences will survive and reproduce.
- Pass on their advantageous alleles to their offspring.
(evolution)
103
Why is variation important in artificial selection?
- Phenotypic variation gives some individuals characteristics that humans find desirable.
- Bred for centuries to produce a variety of plants and animals that have proven useful to people.
104
Population
This is a group of individuals of the same species that can interbreed.
105
Gene pool
This is the total number of alleles present within the population.
106
Allele frequency
This is the number of alleles of a certain type present within the population.
107
What factors affect the genetic variation within a population?
- Genetic drift
- Migration
- Natural selection and competition
- Random mating
108
What assumptions are made when using the Hardy-Weinberg principle?
- The population is very large
- Mating is random
- No selective advantage of any genotype
- There is no mutation, genetic drift or migration.
109
Natural selection
This is the mechanism that drives evolution, whereby advantageous alleles are more likely to be passed on to the offspring.
110
Evolution
This is the change in allele frequencies of a species over time.
111
Selection pressure
This is an environmental factor that allows certain individuals in the population to live until their reproductive age.
112
Genetic drift
This is the loss of an allele due to chance.
113
Wha types of reproductive isolation are there?
Location/temporal/seasonal/reproductive mechanisms
114
How isolating mechanisms can lead to a new species?
- Isolating mechanisms creates two sub-population.
- Different alleles will be eliminated or increased in each sub-population.
- Over time, genetic differences with accumulate between the two sub-groups.
- These two sub- groups will not be able to interbreed.
115
What are two selection pressures involved in natural selection?
Stabilising and directional
116
What is stabilising selection?
This is when the environment selects against novel phenotypes and maintains the existing phenotypes.
117
What is directional selection?
This is when the environment changes and individuals with advantageous phenotypes are selected for.
118
What effect would genetic drift have on a population?
- Decrease genetic variation
- Lead to extinction
- Lead to evolution of a new species
- Reduce the ability of a population to survive environmental changes.
119
The biological species concept
A group of similar organisms that can interbreed to produce fertile offspring.
120
The phylogenetic species concept
A group of organisms that have similar morphology, physiology, behaviour, embryology and occupy the same ecological niche.
121
A monophyletic group
A group of organisms that contains the most recent common ancestor and all of the descendants.
122
A paraphyletic group
A group of organisms that contains the most recent common ancestor, but excludes some of the descendants.
123
What is cladistics?
A hierarchical classification of species, based on the evolutionary relationships.
124
What does cladistics focus on?
Evolutionary relationships
125
What type of analyses are favoured?
Objective and quantitative methods.
126
What is needed for cladistic studies?
DNA and RNA sequencing and computer programming.
127
What are the similarities between natural and artificial selection?
The processes contribute to the evolution of the species and can alter the frequency of alleles in the gene pool.
128
What can only natural selection do?
- The rate of phenotype change is slow.
| - The environment is then selective agent.
129
What can only artificial selection do?
- The rate of phenotype change is fast.
| - Humans are the selective agent.
130
What are the disadvantages associated with artificial selection of dairy cows?
- Genetic variation reduced within the population
- Increase chance of inbreeding (homozygous recessive individuals for deletion traits)
- Increased health problems
- Public concern over hormone use for superovulation.
131
What are two examples of artificial selection?
Production of the dairy cow and production of bread wheat
