Genetic Information Flashcards
(107 cards)
1
Q
Describe a DNA molecule
A
- Double stranded
- Each nucleotide in the strand comprises of a phosphate, deoxyribose sugar and a nitrogenous base
- The bases from one strand pair in a complementary fashion with the bases on the other strand (adenine pairs with thymine, guanine with cytosine)
- Millions of base pairs long
2
Q
Where is DNA found in prokaryotes?
A
Prokaryotic (bacterial) cells have a single molecule of DNA formed into a circle. Some cells also have smaller loops called plasmids. The DNA is naked and is not associated with histone proteins
3
Q
Where is DNA found in eukaryotic cells?
A
- DNA is found in the nuclei of eukaryotes, in a very long linear molecule which is associated with histone proetins
- DNA is also found in the chloroplasts and mitochondria in eukaryotes in a short circular molecule, not associated with histone proteins
4
Q
Together what do DNA and histone proteins form?
A
A chromosome
5
Q
How is the DNA and histone proteins arranged to form a chromosome?
A
The DNA molecule is wrapped around the histone proteins to fix it into position, the DNA histone complex is then coiled into solenoids and then further coiled. This means that a very long molecule can be condensed into a single chromosome (lots of genetic information can be stored in the nucleus of each cell
6
Q
When can a chromosome be seen as a distinct structure?
A
When the nucleus is about to divide and the DNA molecule is already replicated by semi-conservative replication (this is prophase of the cell cycle)
7
Q
What is a diploid organism?
A
An organism that inherits the full set of chromosomes from each parent, as a consequence diploid cells have homologous pairs of chromosomes
8
Q
What diploid number do humans have?
A
2n=46
9
Q
What is it called when one member of the pair is inherited from the mother?
A
Maternal chromosome
10
Q
What is it called when one member of the pair is inherited by the father?
A
Paternal chromosome
11
Q
What is a homologous pair of chromosomes?
A
Carry the same genes at the same locus but do not necessarily carry the same alleles of a gene. They are not genetically indentical
12
Q
What is a gene?
A
A base sequence of DNA that codes for either:
1 - The amino acid sequence of a polypeptide
2 - A functional RNA (including rRNA and tRNA)
13
Q
Describe the structure of a gene
A
- A gene occupies a fixed position called a locus on a particular DNA molecule. One DNA molecule carries many genes
- In eukaryotes most of the DNA molecule does not code for amino acid sequences in the polypeptides (on 2% in humans). There are non-coding multiple repeat sequences between genes
- Not all of the base sequences within genes codes for amino acid sequences.
14
Q
Which part of the genes code for amino acid sequences?
A
Exons
15
Q
Which part of the genes do not code for amino acid sequences and are separated by one or more coding sequences?
A
Inrons
16
Q
Define the term genome
A
The complete set of all the genes in a cell, including the genes in the nucleus, mitochondria and chloroplasts
17
Q
Define the term proteome
A
The full range of all the proteins that a cell is able to produce using its genome
18
Q
Define the term allele
A
Some genes have two or more alternative forms, each allele has a different sequences of bases and consequently codes for a different polypeptide
19
Q
Define the term gene pool
A
All of the different alleles of all the genes found within a population
20
Q
How many bases in a gene sequence code for a specific amino acid?
A
Every 3 bases forms a triplet that codes for 1 amino acid
21
Q
How many possible combinations of triplets are there?
A
4x4x4 = 64 possible combinations
22
Q
What is meant by the term degenerate?
A
Some amino acids can be coded for with different triplets e.g. AGA and AGG both code for ‘ARG’
23
Q
What does the fist triplet always code for?
A
Methionine
24
Q
Why do only 61 triplets code for amino acids out of the 64 possible combinations?
A
3 of the triplets are stop triplets
25
Where is a stop triplet always found?
At the end of each gene
26
What is meant when saying the code is universal?
It is the same in all organisms
27
What is meant when saying the code is non-overlapping?
Each base is read only once, each base is [art of only one triplet
28
What two types of RNA are needed in addition to the DNA to synthesise proteins?
mRNA and tRNA
29
Describe RNA molecules
- Single stranded polynucleotide
- The nucleotides comprise of a phosphate, a ribose sugar and one of 4 nitrogenous bases - adenine, uracil, guanine and cytosine
- Phosphodiester bonds between nucleotides
30
How many nucleotides long is mRNA?
Up to a few thousand nucleotides long
31
What is every 3 bases named in mRNA?
A codon
32
How many nucleotides long is tRNA?
About 75 nucleotides long ,
33
Describe a tRNA molecule
- The strand folds back on itself and hydrogen bonds form between complementary base pairs
- The overall shape is called clover leaf
- Three bases are exposed, these are called the anticodon
- The anticodon on a tRNA molecule bonds to a complementary codon on a mRNA nmolecule during the process of translation
34
What is the first step to making proteins?
Transcription
35
What does transcription do?
It makes a molecule of pre-mRNA, the whole gene is transcribed including the introns as well as the exons
36
Describe the process of transcription
- One gene unwinds due to hydrogen bonds between complementary bases being broken
- Complementary free RNA nucleotides bind to the exposed bases on the template strand e.g. A-U, T-A, C-G and G-C
- The sugar phosphate backbone between the free RNA nucleotides is joined using RNA polymerase (creates phosphodiester bonds)
- Transcription stops at a stop triplet such as ATC. This marks the end of a gene and causes the disengagement of the RNA polymerase
- A gene is transcribed repeated to make many pre-mRNA at any time
- Most genes are transcribed to make pre-mRNA however a few genes are transcribed to make rRNA and tRNA
37
What is the second stage of making a protein?
Splicing mRNA
38
Where does transcription take place?
In the nucleus
39
Where does splicing take place?
In the nucleus
40
Describe splicing mRNA
pre-mRNA is made into mRNA
- In eukaryotes nulcei the pre-mRNA is then spliced, the non-coding sections are cut out and the coding sections are edited together to produce mRNA which is a copy of the exons only
- Prokaryotic DNA and mitochondrial and chloroplast DNA does not have introns so the mRNA does not need splicing
41
What does translation do?
Makes polypeptides
42
Where does translation place?
Either in the cytoplasm or RER
43
Describe the 5 parts to translation
1.
- Ribosome binds to first 2 codons on the mRNA - A tRNA carrying methionine comes to ribosome
- The anticodon on the tRNA binds to the complementary codon on the mRNA
2.
- A second tRNA binds to the next codon, the tRNA is carrying a specific amino acid
3.
- The two amino acids undergo a condensation reaction and a peptide bond forms between them
4.
- The first tRNA then leaves the ribosome and picks up another amino acid
- The ribosome moves along the mRNA to cover the next codon
- The anticodon of another tRNA, again carrying a specific amino acid, binds to the next codon
- The amino acid binds to the growing polypeptide chain
5.
- When the ribosome reaches a stop codon it disengages from the mRNA. There are no tRNA with anticodons complementary to stop codons
44
Is ATP required for translation? If so, which part?
Yes, ATP is required to provide the energy for the bond formation between the amino acid and the tRNA molecule, allowing the tRNA to carry an amino acid to the ribosome during translation
45
Describe the experiment conducted to show that DNA rather than proteins carried the genetic code
- Using bacteriophage viruses (a virus that binds to the surface of bacteria and passes DNA into the cell, the proteins remains outside the cell)
- The viral DNA then uses the amino acids, nucleotides and ribosomes in the cell to make new viruses. The new viruses break out of the cells and destroy it
- Scientists made viruses that had DNA with a radioactive isotope of phosphorus in it and proteins with a radioactive isotope of sulfur in them
- The viruses were allowed to infect bacteria then they bacteria were tested to see whether or not they had taken up the DNA or proteins
- It was found that the radioacive sulfur was only found outside the cell whereas the radioactive phosphorus was inside
- This experiment indicates that the genetic code is carried by the viral DNA
46
What experiment was used to work out the genetic code?
- They made 3 types of mRNA (AAA,UUU,CCC) and added all 20 amino acids attached to tRNA, one of which was phenylalanine which was labelled with a radioactive isotope of carbon but the others weren't
The results showed that UUU had an extremely high radioactivity count of polypeptide produced
- This process was repeated using different radioactively labelled types of amino acids and different mRNA each time
47
How many divisions are there in meiosis?
2
48
What happens first in meiosis?
DNA replication to form homologous pairs of chromosomes (sister chromatids)
49
What happens in the first division of meiosis?
- Crossing over
| - Independent segregation
50
Describe the process of crossing over
- Occurs in meiosis I
- The homologous chromosome pair come together to form a bivalent
- Non-sister chromatids wrap around each other and attach at points called chiasmata
- The chromosomes break and re-join swapping sections of non-sister chromatids - this is crossing over
- This leads to new combinations of alleles in gametes
51
Describe the process of independent segregation
- Occurs in meiosis 1
- Homologous pairs of chromosomes randomly align at the equator of the cells and then the pair separates to opposite poles of the cell
- The paternal and maternal chromosomes of one pair segregate independently from the other pairs
- The number of different maternal and paternal chromosomes in the gametes is 2^n where n is the number of pairs of chromosomes e.g. in a species where on 2 pairs of chromosomes there are 2^2 = 4 possible combinations of maternal and paternal chromosomes in the gametes
52
Calculate how many possible combinations of chromosomes there are in humans
2^23 = 8,388,608 possible combinations
53
What is genetic diversity?
The number of different alleles of genes present in a population
54
What is an allele?
A different variation of a gene
55
What is an adaptation?
A characteristic that increases an organism's chance of survival/reproductive success
56
What 3 possible types of adaptations can there be?
- Anatomical
- Physiological
- Behavioural
57
Give examples of each type of adaptation
Anatomical e.g. formation of wings, lots of muscle
Physiological e.g. enzymes
Behavioural e.g. less aggressive to other animals
58
What are genetic bottlenecks?
- Events that cause a big reduction in a population
- This causes the number of different alleles in the gene pool
- Results in low genetic diversity
- When the population increases the genetic diversity will still be low
59
What is the founder effect?
- When a small founder population becomes isolated from the original population
- The small founder population will have a smaller gene pool and genetic diversity than the original population
- When the population increases the genetic diversity will still be low
60
What is stabilising selection?
- Where it is more beneficial to have phenotypic characteristics towards the middle of the range in the population
- The individuals with these characteristics are more likely to survive and will therefore be more likely to pass on their beneficial characteristics
- The normal distribution curve moves in towards the centre
- E.g. birth weight of humans
61
What is directional selection?
- Individuals with alleles which give a characteristic of an extreme type are more likely to survive and reproduce
- The normal distribution curve shifts in the direction of the extreme
- E.g. antibiotic resistance of bacteria
62
What 5 things cause genetic diversity?
- Gene mutations
- Chromosome mutations
- Crossing over
- Random assortment
- Random fusion of gametes
63
What does a gene mutation involve?
A change in the base sequence of a chromosome
64
When do mutations usually occur?
During DNA replication
65
What may happen when a mutation occurs within an exon of a gene?
The polypeptide coded for may be changed in structure and consequently be non-functional
66
What is a neutral mutation?
If the change in amino acid sequence does not affect the function of the protein
67
What are the 3 types of mutations?
- Substitution
- Addition
- Deletion
68
What is a substitution mutation?
When one or more bases in a gene sequence are exchanged for others, this results in a change in a base triplet
69
What is an addition mutation?
One or more bases are added to the base sequence, this results in a frame shift
70
What is a deletion mutation?
One or more bases are deleted from the base sequence, this results in a fame shift
71
What is a silent mutation?
When the mutation causes no change in the polypeptide
72
What is a mutagenic agent?
Something which increases the rate at which mutations occur
73
Name some mutagenic agents
- High energy radiation e.g. ultraviolet light
- Ionising radiation e.g. gamma and x-rays
- Chemicals e.g. tar, bromine, peroxide, benzene
- Viruses e.g. HPV
74
Define the term species
A group of similar organisms able to reproduce to give fertile offspring
75
What is courtship behaviour?
A stereotypical action that allows one another to recognise as being from the same species
76
What are the advantages of courtship behaviour?
Allows animals to recognise and mate with adults of:
- Opposite gender
- Same species
- Healthy and in good breeding condition
77
Describe the courtship behaviour of the three spine sickle back
1 - The female recognises a female with a swollen belly showing she has many eggs
- He attracts her to his nest with a zig-zag dance recognised by only a female sickle back
- The female responds to the zig-zag dance especially if the male has a strong red colouring showing he is in good breeding condition
2 - The male encourages the female to enter his nest
3 - The male quivers against the female's sides to encourage her to spawn (release her eggs)
4 - The male then enters the nest and chases her out, he releases his sperm to fertilise the eggs
- The female swims away and leaves the eggs to the care of the father
78
Using examples of birds and insects, explain their courtship behaviours
Birds - perform dances
| Insects - pheromone secretion
79
How are organisms classified?
- Into taxa (series of categories
| - The categories are hierarchical
80
What is meant by the term hierarchical?
Each organism is classified into a series of smaller and smaller taxa with no overlap between the taxa
81
Name all of the categories of classification?
- Domain (Do you want)
- Kingdom (King)
- Phylum (Prawn)
- Class (Curry)
- Order (Or)
- Family (Flame)
- Genus (Grilled)
- Species (Steak)
82
Name the categories of domain
- Eukarya
- Archaea
- Bacteria
83
Name the categories of kingdom
- Aminalia
- Plantae
- Fungi
- Protoctista
- Prokaryota
84
Name the categories of phylum
- Chordata
- Molluscs
- Arthropods
- Nematodes
85
What is meant by a binomial name and what are humans' binomial name?
- The final two taxa are used to give the binomial name genus and species
- A human's binomial name is Homo sapiens
86
What do phylogenic trees show?
The common ancestors of organisms and how closely related they are
87
What 5 ways is it possible to differentiate how closely related organisms are?
- Physical appearance
- Immunological comparisons
- Comparing DNA sequences/genome sequencing
- Comparing mRNA sequences
- Comparison of amino acid sequences in proteins
88
Define the term biodiversity
The variety of living organisms in an area
89
What type of biodiversity is desirable?
High biodiversity
90
Where is global diversity highest?
At the equator
91
Define the term community
A group of interacting populations of different species living in the same area at the same time
92
Define the term population
A group of organisms belonging to the same species found in the same at the same time and potentially able to interbreed
93
Define the term habitat
The environment in which an organism or population of organism usually lives
94
What is species richness?
A measure of the number of different species in a community
95
How does physical appearance dictate an organisms taxa?
If organisms look similar this infers genetic similarities meaning they are more closely related
96
What are immunological comparisons and how is it possible to classify organisms using this?
- When antibodies of one animal are added to proteins from another the antibodies will bind if the proteins are similar in shape
- The more closely related two organisms, the more similar the shape of their proteins will be and the more likely the antibodies will bind to them
- When antibodies bind they usually precipitate out - the more precipitate the more similar the organisms
97
How is it possible to classify organisms when comparing DNA sequences/genome sequencing?
- It is the process of finding the sequence of bases in the DNA of an organism
- Has become much faster and cheaper in recent years (due to improvement in technology and computers)
- The more similar sequences are the more recently the two species shred a common ancestor with the same sequence
98
What are the benefits of comparing mRNA than DNA sequences?
- mRNA easier to extract from a cell than DNA as it is found in the cytoplasm and many more copies will be present
99
How is it possible to classify organisms by comparing amino acid sequences in proteins?
- The amino acid sequence is determined by the DNA gene sequence of the organism
- Closely related species have very similar DNA sequences and consequently very similar amino acid sequences
- Cytochrome C is a protein found in the majority of organisms
100
What is the equation for calculating the index of biodiversity?
Look in genetic information booklet
101
What does the value of the index of biodiversity suggest?
Higher value indicates a more biodiverse environment
102
Define the term conservation
Actively managing ecosystems in order to increase biodiversity
103
Define the term monoculture
Large fields growing only a single crop
104
How do intense farming techniques affect biodiversity within an environment?
Often results in lowering the biodiversity
105
Name all 6 intense farming techniques and explain the effects of this
Clearing woodland - to increase land available for cultivation or grazing. This not only reduces the number of species of trees it also reduces the variety of habitats leading to a decrease in animal diversity
Removing hedgerows - to enlarge field and increase the area available for agriculture, hedges can also compete with arable crops for light. Leads to loss of habitat for wildlife and reduction in insects and birds. Hedges also act as corridors for wild animals to use to move around an area safely and to meet other animals from other areas during mating season
Spraying pesticides - on crops to kill invertebrates which eat the crop. This kills not only the pests but the pollinating insects such as butterflies and bees
Spraying herbicides - to kill weeds which compete with the crops. This kills the plants which are at the bottom of the food chain, animals higher up reduce in number due to lack of food
Improving grazing land - Loss of habitat for invertebrates and small animals
Growing monocultures - Just one crops over large area greatly reduces the variety of habitats and biodiversity
106
What conservation measures are encouraged to maintain high biodiversity and a wide range of habitats?
- Environmental Stewardship Scheme encourages farmers to replant hedgerows and to leave margins around their fields
- The EU has banned the use of various insecticides
- Endangered species such as the hen harrier are protected and killing them is a criminal offence
- Intensive agricultural development in areas which have been declared National Parks e.g. Lake District, Sites of Special Scientific Intrest or Areas of Outstanding Natural Beauty e.g. forest of Bowland
107
Define variation
The differences that exist between individuals within a species and between differet species
