Topic 4: Genetic Info, variation + relationships Flashcards
1
Q
Why is DNA a suitable molecule to carry genetic info?
A
- DNA is a very stable molecule, so it rarely changes (/mutates)
- DNA is a large molecule (polymer) so lots of info is carried
2
Q
What reaction joins the 3 components of DNA together?
A
Condensation reactions
3
Q
How do two adjacent nucleotides join together?
A
By a condensation reaction, forming a phosphodiester bond
4
Q
What type of bond joins two opposite nucleotides together?
A
H bonds
5
Q
How many different Amino Acids are there in lining organisms?
A
20
6
Q
What ditermines the number + sequence of AAs in each polypeptide?
A
DNA base sequences, 3 DNA bases code for one AA
7
Q
Why might a virus have a different % of adenine to thymine?
A
Viruses have single-stranded DNA
8
Q
How is the structure of DNA related to its function?
A
- The sugar phosphate backbone prevents physical + chemical damage
- H bonds are individually weak, so DNA Helicase can break them
- Large molecule, holds lots of info
- Double-stranded, allows semi-conservative replication
- Complementary base pairs allows accurate replication
- Compact for storage
9
Q
What is DNA like in Prokaryotes?
A
Shorter
Circular
No Histones (not associated with proteins)
ALL (non-viral) DNA IS DOUBLE-STRANDED
10
Q
What is DNA in Eukaryotes like?
A
Protein-bound (histones)
Linear
V. Long
11
Q
What are the components of chromosomes?
A
DNA (nucleotides) and associated proteins (Histones)
12
Q
What is the DNA like in mitochondria and chloroplasts?
A
Same as prokaryotic DNA
13
Q
What is the monomer of DNA?
A
Nucleotides
14
Q
What is a gene?
A
A section of DNA with a sequence of nitrogen bases that carries a code
15
Q
What do genes code for?
A
- Polypeptides
2. Functional RNA (tRNA and mRNA)
16
Q
What is a locus?
A
The position of a gene on a chromosome
17
Q
What is a chromatid?
A
2 Identical copies of the same gene found on a chromosome
18
Q
What is a centromere?
A
Part of the chromosome that joins together two chromatids
19
Q
What two processes, in order, are involved in creating polypeptides from DNA?
A
Transcription (DNA to mRNA)
Translation (mRNA to Protein)
20
Q
What is the primary structure of protein?
A
The number and sequence of AAs
21
Q
Why is the primary structure of proteins important?
A
It determines the location of Hydrogen, Ionic and Disulphide bonds which form between AAs.
The location of these bonds determines the secondary and tertiary structure of the protein
22
Q
What are the names of the 4 nitrogen bases in DNA? Which ones pair up?
A
Adenine + Thymine,
Guanine + Cytosine
23
Q
What is the formula for calculating the no. of amino acids that can be coded for when there are 4 nitrogen bases being read in groups of 3?
A
4 ^3 = 64
24
Q
What would happen to the sequence of AAs in a polypeptide if the nitrogen base sequence was altered?
A
The AA base sequence in the polypeptide MAY change, it depends on the type of mutation because the genetic code is degenerate
25
Why is the genetic code said to be degenerate?
There are 64 possible triplet codes, but on 20 AAs, thus some AAs have multiple triplet codes.
eg TTT and TTC both code for Phe
26
What causes a stop codon?
Triplet codes that do not code for an AA, so no AA is added to the polypeptide chain - causing it to stop
27
What does degenerate mean?
One AA may be coded for by >1 triplet code
28
Why is the genetic code "non-overlapping"?
It is read every group of 3, not in between
29
Why is the genetic code universal?
The same DNA triplet codes for the same AA in (nearly) all organisms
30
What are mutations?
Changes to the nitrogen base sequence of DNA
31
What 4 factors cause DNA to mutate?
- Spontaneous mutations upon replicating
- Chemicals
- Biological agents
- Radiation
32
What is a frame-shift mutation?
A mutation which causes the code to be read differently after the point of mutation
33
What causes an insertion mutation?
Extra nitrogen bases being added
34
What causes a deletion mutation?
Nitrogen bases being removed
35
What causes a substitution mutation?
Nitrogen bases being replaced with different nitrogen bases
36
Which type of mutation may have no effect of the function of a protein? Why?
Substitution mutations
| The genetic code is degenerate, so the same AA COULD still be coded for, so the corresponding protein will be the same
37
Why might a frame-shift (deletion/insertion) mutation have a greater effect if it is near the start of a gene?
The mutation may change the type of AA after the point of mutation (or cause a stop codon), so different bonds will form in different places, so the protein structure will change
38
Where can non-coding DNA be found?
In genes or between genes
39
What is the non-coding DNA found between genes called?
VNTRs (repeated units of the same base sequence)
40
What is the non-coding DNA found within genes called?
Introns (only in Eukaryotes)
41
What is the coding DNA found within genes called?
Exons (only in Eukaryotes)
42
Do porkaryotes have Introns and exons?
No
43
What is the genome of a cell?
The genetic material of an organism, consisting of DNA (but RNA in some viruses). Includes both genes and non-coding DNA
44
What is the proteome of a cell?
The entire set of proteins expressed by a genome, cell, tissue or organism at a certain time
45
In Transcription, what enzyme unzips DNA? How is this done?
DNA Helicase
| Hydrogen bonds are broken
46
After DNA is unzipped by helicase in transcription, what happens next?
RNA nucleotides align themselves with one of the DNA strands (template strand), forming H bonds with the exposed bases
47
What RNA nucleotide is complementary to Adenine in DNA during transcription?
Uracil (instead of thymine)
48
Where does transcription take place?
Inside the nucleus of a cell
49
Where does translation take place?
In ribosomes in the cytoplasm or on the rough ER
50
How does mRNA leave the nucleus?
Via the nuclear pore
51
What enzyme joins adjacent RNA nucleotides together in transcription?
RNA polymerase
52
What happens to pre-mRNA before it leaves the nucleus?
It is spliced to remove introns
53
What does splicing do (transcription)?
Introns are removed (leaving exons) from pre-mRNA before it leaves the nucleus via a nuclear pore
54
Why does RNA polymerase only work in one direction?
- It is an enzyme
- Has a specific active site due to specific tertiary structure
- The active site only binds to complementary-shaped RNA nucleotides (the substrate)
- It would not fit going the opposite direction
55
How is mRNA adapted to its function?
- Small, can move of the the nucleus into cytoplasm, via nuclear pore
- Contains 4 nucleotides, carries the genetic code
- Unstable, so hydrolysed quickly when no longer required, ensures that the cell doesn't waste energy making proteins it doesn't need
56
What is a transcription factor?
A protein/molecule that binds to specific DNA base sequences (promoter region), controlling the rate of transcription
57
How do Transcription Factors (TFs) act? (3 steps)
1. TFs move from the cytoplasm to DNA
2. Bind to promoter region on DNA
3. Allows/ blocks the binding of RNA polymerase
58
What is a promoter region?
A region of DNA that RNA polymerase and TFs bind to to animate transcription
59
How does transcription in prokaryotes differ from eukaryotes?
- mRNA directly produced in prokaryotes (no splicing as there are no introns)
- Splicing is required in eukaryotes, so pre-mRNA is involved
60
What is an intron?
A region of DNA within a gene that does not code for amino acids
61
What is splicing?
The joining together of exons to produce mRNA ready for translation in the cytoplasm
62
Describe the structure of transfer RNA (tRNA)
- Single stranded
- Folded back on itself, leaving 3 unpaired N bases
- The 3 unpaired bases form an anticodon, complementary to the codon on mRNA
- H bonds form where the RNA polynucleotides fold
A clover leaf structure
63
What is the function of tRNA?
To carry specific amino acids in translation, complementary to the codon on mRNA
Forms a tRNA amino-acid complex
64
What reaction causes a peptide bond to form?
Condensation reaction to form a peptide bond
65
What are ribosomes made of?
2 sub-units: One large, one small
66
Do ribosomes occur singly?
No. Can be connected in groups called polyribosomes, connected by ribosomal RNA (rRNA)
67
How is tRNA adapted to its function?
- Has amino acid binding site, allowing AAs to be carried in the cytoplasm
- Anticodon is complementary to codons on mRNA, the pairing of codons with anticodons determines the order of AAs
- tRNA is more stable than mRNA, so it can be used multiple times to pick up the same AA several times
68
What types of bond form in the secondary structure of proteins?
H bonds
69
What are the two types of secondary protein structure?
Alpha helix
Beta-pleated sheets
70
What 3 types of bond form in the tertiary structure of proteins, in order of strength?
H Bonds
Ionic bonds
Disulphide bonds
71
What is the structure proteins made up of >1 polypeptide called?
A Quaternary structure
72
How does the structure of tRNA differ form mRNA?
- tRNA has some hydrogen bonds form at the anticodon region (no H bonds in mRNA)
- tRNA has a cloverleaf structure, mRNA is linear, single stranded
73
Where does splicing take place?
In the nucleus
74
What happens during translation?
mRNA is read at ribosomes, allowing AAs to be joinde together to make a polypeptide
75
What are the 6 steps of translation?
1. mRNA attaches to a ribosome and tRNA carries AAs to it
2. The tRNA molecule carrying the AA joins to mRNA by complementary base pairing between the anticodon and condon respecively
3. A second tRNA + corresponding AA joins in the same way
4. The two AAs are joined by a peptide bond
5. The first tRNA moves away, leaving the AA behind
6. Another tRNA and comp AA join and the process continues until a stop codon is read and the polypeptide separates
76
What 'tells' the cell to start and stop translation?
The start and stop codons respectively
77
Why are individuals of the same species different from each other?
Variations in DNA (different alleles of the same genes)
78
Why is genetic variation important?
It may lead to adaptations the improve the chances of organisms'/species' survival
79
What is genetic diversity?
- Total number of different alleles in a population
| - The more alleles in the population, the greater the genetic diversity
80
What is a gene?
The base sequence of DNA that codes of amino acids (polypeptides) or a functional RNA (tRNA or rRNA)
81
What is an allele?
An alternative form of the same gene
82
Why can mutations sometimes be good?
Some mutations may be beneficial to an organism, coding for a protein which give an individual an advantage in certain conditions
83
What are the two GENERAL types of mutation
1. Gene mutation
| 2. Chromosome mutation
84
What is a gene mutation?
A change to one or more nucleotide bases or sequence of bases within a gene
85
What is a chromosome mutation?
A change in the structure or number of chromosomes
86
What is something that increases the rate of mutations?
A mutagenic agent
87
How might a substitution mutation of one AA cause a faulty protein to be formed?
- Substituted AA may not form the same H/ionic/disulphide bonds
- The tertiary structure of the protein changes
- The function of the protein may also change if the functional site changes shape too
88
Give and example of a disorder caused by a substitution mutation.
(for essays...)
Sickle Cell Anaemia
Causes Haemoglobin to stick together so red blood cells block capillaries
89
Why do substitution mutations sometimes not cause any change to the amino acid in a polypeptide?
- The genetic code is degenerate
- The substitution may code for the same AA
- So the protein will be the same shape (reference bonds)
90
What is non-disjunction?
When individual homologous chromosomes fail to separate during meiosis - the resultant gamete has one more or one less chromosome than normal
91
What 5 things need to be covered when explaining the effect of mutations on proteins/enzymes
1. Nature of the mutation (frame-shift) causes the base sequence of the gene to change
2. Causes different AAs to be coded for in protein synthesis
3. H/ionic/ disulpide bonds form in different places
4. Protein folds differently
5. Tertiary structure changes so active/functional site no longer complementary to substrate
6. Reference the effect on the metabolic pathway etc
92
What does MITOSIS result in?
- 2 genetically identical daughter cells
| - Same number of chromosomes (DIploid)
93
What does MEIOSIS result in?
- 4 genetically different daughter cells
- Each cell has half the no. of chromosomes (HAploid)
- Produces gametes
94
What is the purpose of mitosis?
For growth and repair of cells and tissues
95
What is the purpose of meiosis?
- Produces gametes
| - Introduces genetic variation in offspring
96
How does meiosis cause genetic variation?
- Crossing over of alleles
- Independent segregation of homologous chromosomes
- Random fertilisation of gametes
97
What is meant by 'diploid'?
Chromosomes in homologous pairs
98
What are homologous chromosomes?
- Two chromosomes carrying the same genes (One from each parent)
- The chromosomes carry a different allele of each gene
99
What is an allele?
An alternative form of a gene
100
What are the two general stages (1 and 2) of meiosis?
1. Separation of homologous chromosomes
| 2. Separation of chromatids
101
What happens in prophase 1 of MEIOSIS?
- Chromosomes coil up and become visible
- Spindle fibres form
- Homologous chromosomes pair up
- Chromatids wrap around each other (crossing over and recombination)
- Genetic material is exchanged at chiasmata
102
What happens in metaphase 1 of MEIOSIS?
- Homologous pairs of chromosomes line up on the cell equator
103
What happens in anaphase 1 of MEIOSIS?
One of each homologous pair (still 2 sister chromatids) moves to each pole
104
What is the random alignment of homologous chromosomes in metaphase 1 of MEIOSIS called?
Independent assortment
105
What happens in telophase 1 of MEIOSIS?
2 daughter cells form, each with one of each pair of homologous chromosomes
106
What happens in meiosis 2?
Sister chromatids separate (like in mitosis) to make 4 haploid daughter cells
107
What two processes cause variation in meiosis?
Crossing over
Independent segregation
108
What is independent segregation (meiosis)?
The random alignment of pairs of homologous chromosomes along the equator of the cell
109
What is a population?
A group of individuals of the same species living in the same place.
Can breed to produce fertile offspring
110
What is a gene pool?
All the genes and their various alleles that exist in a population at a specific time
111
What is alllele frequency?
The number of times the allele of interest is observed in all the alleles of a gene in a population
112
What causes high genetic diversity?
A great variety of alleles in a population
113
Why is high genetic diversity important?
There are a large variety of alleles, and this characteristics (phenotypes) in a population so more individuals will survive if the environment changes
(by natural selection)
114
What 5 points are required in an answer on natural selection?
1. Random mutation = New allele which is advantageous in certain environments (introduces variation)
2. Individuals with new allele are better adapted to the environment, surviving more competition
3. Individuals with allele survive and reproduce to pass on allele to next generation (REPRODUCTIVE SUCCESS)
4. Next gen also have allele and thus survive + reproduce
5. Allele frequency increases over many generations as breeding success also increases
115
What is selection?
The process whereby organisms that are better adapted to the environment survive and breed. Those without the adaption will not
116
What does phenotype mean?
- The characteristic that comes form a combination of alleles
- Observable physical and chemical characteristics of an organism
117
What is directional selection?
Selection for a particular characteristic may favour individuals that vary in one direction away from the mean of the original population
The normal distribution curve will move from the mean as the environment changes and individuals without advantageous allele will not survive and thus reproduce
118
What is an example of directional selection?
Antibiotic resistance in bacteria
119
TRUE OR FALSE
Bacteria mutate because of antibiotics
FALSE
- Bacteria may possess a mutant allele prior to exposure to antibiotics and thus survive
- Mutations are random and the effectiveness of a mutation depends on the environmental circumstances
120
What sort of selection occurs in stable environmental conditions?
Stabilising selection
121
What occurs in stabilising selection?
Individuals with phenotypes closest to the mean are more likely to survive and pass on their alleles to the next gen
Those with phenotypes at the extremes are less likely to do so
122
What is an example of stabilising selection? How does it work?
Human birth weights
Babies with low birth mass loose heat + susceptible to disease. Babies of larger mass are more difficult to deliver. Babies of medium mass will survive
123
In what way does stabilising selection affect the genetic diversity of a population?
Less diverse because phenotypes at extremes are eliminated
124
What effect does stabilising selection have on the SD and mean of populations?
SD becomes smaller, mean unchanged
125
What effect does directional selection have on the SD and mean of populations?
SD unchanged, mean translated to favourable phenotype
126
What are the similarities between Mitosis and Meiosis?
- Both involve DNA replication in S phase of interphase
| - Both use PMAT (Prophase, Metaphase, Anaphase and Telophase) although the processes do differ
127
What are the differences between Mitosis and Meiosis?
- Meiosis involves 2 divisions (2x PMAT)
- Meiosis produces 4 haploid gametes (variation)
- Mitosis creates 2 genetically identical cells
128
What is a species?
- Similar to other members of the same species (physically and biochemically)
- Occupy the same ecological niche
- Can breed to producing living, fertile offspring
129
What is taxonomy?
The science of classification
130
Why is taxonomy important?
- There are millions of species on earth
- Many have similar features
- Allows humans to organise groups by features
131
What does a phylogenetic system do?
Organises species by evolutionary relationships
132
What is a binomial (in terms of taxonomy)?
Two name
Homo sapiens
(First word capitalised; both in italics or underlined)
133
What is the advantage of using a binomial system?
- Clarity (avoids confusion with common names)
- Stability (Latin name meanings don't change)
- Unique for each species
- Universally used worldwide
134
What is the order of taxa?
```
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
```
135
What is a mnemonic for remembering the order of taxa?
```
D
King
Prawn
Curry
Or
Fairly
Greasy
Sausage
```
136
What contains more organisms family or class?
Class because it is higher in the hierarchy than family
137
Why is courtship behaviour important for mating?
- Allows animals to recognise members of the same species
- Identifies a mate that is capable of breeding
- To form a pair bond to successfully raise young
- Syncronises mating
138
How can scientists determine evolutionary relationships nowadays?
- Genome sequencing on electrophoresis gel
| - Immunology
139
How DID scientists determine evolutionary relationships in the past?
By observation alone because of lack of technology
140
Why do changes to gene sequences allow the relationships between organisms to be made?
The more recent the common ancestor is, the less time has passed between the gene of the two species, so less mutations have (occurred in less time)
141
When establishing differences between species why must the same gene be compared?
- Similar base sequence (some bases in common)
| - Complementary bases will bind together by H bonds
142
Besides DNA sequencing, what other techniques are used to determine the relationship between species?
1. mRNA sequencing (only expressed genes as introns are removed during splicing in transcription)
2. Protein sequencing
143
Is it better to use a specific gene to some organisms when comparing genetic relationships or a gene present in all species?
A gene present in all species
eg Cytochrome is a protein involved in respiration so it is present in all eukaryotes. This is more appropriate than haemoglobin because only present in some organisms. Ensures comparisons can be made
144
How can immunology be used to establish evolutionary relationships between organisms?
- Antigens have a similar shape
- Thus tertiary protein structure will be similar
- Primary structure + DNA sequencing will be similar
- Antigens can be tested on antibodies to test the complementary shape (causes antibody antigen complexes to form)
145
What is a population?
- All the organisms of one species
- In a given area
- At a given time
146
What is a community?
- All the populations of different species
- In a given area
- At a given time
147
What is species richness?
The variety of species present in a community
148
What is the index of diversity?
The variety of species present as well as abundance of each species in a community
149
Why is the index of diversity better than species richness?
- Species richness gives no indication of the size of each species' pop
- If a species population is low then it is easier for one individual to die/ not reproduce
150
What 4 farming practices directly affect biodiversity?
1. Removal of hedgerows and woodland
2. Creating mono-cultures
3. Filling ponds and draining marshland
4. Overgrazing land
151
What 3 farming practices indirectly affect biodiversity?
1. Use of pesticides and inorganic fertilisers
2. Escape of effluent
3. Lack of intercropping and crop rotation
152
What is a gene pool?
All the genes in a population
153
Why is it important to maintain genetic diversity?
Some individuals are more likely to survive within a population if the environment changes
154
What two reasons make it ethically wrong to reduce biodiversity?
1. It causes reduction/ loss of populations
| 2. Less organisms present for future generations
155
Name 3 commecial limitations of reduced biodiversity
1. Less medicine
2. Less tourism in biodiversity hotspots
3. Agricultural issues (eg. less pollination)
156
What is selective breeding?
Artificial selection
Individuals with desired characteristics are selected for breeding
157
How does selective breeding affect biodiversity?
Reduces genetic diversity over generations because undesirable phenotypes are not bred
158
What is the founder effect?
1. A new population of only a few alleles is established on an island
2. The population breeds and one allele becomes more frequent through inbreeding
3. Occurs by chance
159
What is a genetic bottleneck?
- Occurs when a disaster reduces a once large population to a small one very quickly
- Only the alleles in the survivors are found in the surviving population
160
What for methods are adopted to compare diversity between species?
1. Frequency of observable characteristics
2. Base sequence of DNA
3. Base sequence of mRNA
4. Amino acid sequence of proteins encoded by DNA and mRNA
161
What must scientists do in order to perform quantitative investigations of variation within a species?
- Collect data from random samples
| - Calculate the mean and SD
162
How can scientists collect samples randomly? (4 steps)
1. Set up a grid
2. Random no. generator to select coordinates
3. Use a large sample size so less influence of chance/anomalies, more representative of the actual population
4. Statistical analysis of the data
163
Why should a large sample size be used when sampling?
Reduces the influence of chance and anomalies so that the sample is more representative of the actual population
164
Why is it important that scientists collect their samples randomly?
- Avoids bias
| - Prevents the desired outcome being prioritised in the sample
165
Why do scientists carry out statistical tests?
To see of their experimental results are due to the independent variable or due to chance alone
166
What does a null hypothesis usually say?
That there is no difference between the data being compared.
Assumes that the differences are due to chance
167
Why is it better to use standard deviation instead of range?
Outliers have more of an effect on range
| SD looks at variation around a mean
168
When would you use a chi-squared test?
When looking at the difference between the data you observe and the data you were expecting
169
When would you use a t-test?
When looking at the difference between two means
170
When would you use a Spearman's rank correlation coefficient test?
When looking for a correlation between an independent variable and a dependent variable
171
What would a null hypothesis for a Chi-squared test be?
"There is no difference between the observed (specify) and expected (specify) values."
(chi-squared looks at the difference between the data you observe and the data you were expecting)
172
What would a null hypothesis for a t-test be?
"There is no difference between mean 1 (specify) and mean 2 (specify)."
(t-test looks at the difference between two means)
173
What would a null hypothesis for a Spearman's rank correlation coefficient test be?
"There is no correlation between the independent variable (specify) and the dependent variable (specify)."
(Spearman's rank looks at a correlation between an independent variable and a dependent variable.)
174
What happens if the value from a chi-squared or t-test calculation is greater than/equal to the critical value?
Reject NH (there is a significant difference)
175
What are gametes?
Haploid cells that combine during fertilisation to form a zygote which subsequently divides + develops into a new organism by mitosis (for growth)
176
Why is meiosis used for sexual reproduction?
It produces haploid daughter cells which then fuse during fertilisation to make a diploid cell with the correct number of chromosomes
177
What does crossing over do to introduce variation?
Each of the 4 daughter cells contains chromatids with different alleles
178
How many divisions does mitosis involve?
1
179
How many divisions does meiosis involve?
2
180
Why doesn't mitosis introduce variation?
There is no crossing over or independent segregation because there is no pairing or separation of homologous chromosomes
181
What (sometimes) causes chromosome mutations?
Errors in mitosis because the homologous chromosomes are not accurately moved to the cell poles (issues with spindle fibres for example)
Called non-disjunction of chromosomes
182
How does genetic diversity increase within populations?
- Mutations in DNA forming new forms of alleles
| - Different alleles being introduced into a population due to migration from other populations (gene flow)
183
What is the founder effect an example of?
A genetic bottleneck
184
What are the three types of adaptation?
1. Behavioural adaptations
2. Physiological adaptations
3. Anatomical adaptations
185
What is an example of stabilising selection?
Human birth weights
186
What does the first branch point on a phylogenetic tree represent?
A common ancestor of all the family members
187
Why is courtship behaviour species specific?
Ensures that only members of the same species respond to the courtship behaviour so that living, fertile offspring are produced
Prevents interbreeding
188
How does courtship help to reduce interbreeding?
- Species specific
- Members of only the same species recognise each other
- Members of other species do not mate, so no infertile offspring are produced
189
What three techniques are used to clarify evolutionary relationships?
1. Genome sequencing
2. Comparing amino acid sequences
3. Immunological comparisons
190
Why is using amino acid sequences to determine evolutionary relationships between organisms less reliable than genome sequencing?
mRNA is spliced in transcription, so whilst the same proteins may be produced, the genetic code may be different because introns are no accounted for
191
What, in basic term, is genetic diversity?
The number of different alleles in a population
192
Why are samples of populations used to study variation?
- A census is time consuming and it will be difficult to catch all the individuals in the group
- Samples can be used as accurate models of the whole population
193
How can samples be less biased?
Using a random sample so that no sample frame is favoured
194
How can a random sample be taken to study the plant species in a field?
Divide the field into a grid and use a random number generator to select coordinates
195
What is a habitat?
The place where an organism lives
