Heredity Flashcards
1
Q
What is the structure of DNA?
A
DNA- Deoxyribonucleic acid.
Double helix molecule
Composed of subunits- nucleotides (sugar,
phosphate, nitrogenous base)
4 bases Adenine (A) Thymine (T) Guanine (G)
Cytosine (C)
A=T, C=G
2
Q
How does DNA fit?
A
DNA can be a very long molecule and as such must be stored effectively. DNA is wrapped around special proteins called histones.
3
Q
What is a chromosome?
A
A chromosome is one single chain of DNA that has been coiled up into a thread like structure. Each chromosome contains a large amount of genetic material in a compact form.
4
Q
What are genes?
A
Within chromosomes there are specific sections which code for specific proteins. These are called genes.
5
Q
What are alleles?
A
Alleles are slightly different from genes. Alleles refer to different versions of genes. They exist on the same positions along the chromosome but code for different proteins.
6
Q
What are introns and exons?
A
Not all of a gene actually codes for a protein. Within genes are two types of DNA:
- Introns – non-coding DNA (The introns are removed when the DNA is converted into mRNA.)
- Exons – coding DNA (This leaves the exon sequences to be coded into proteins.)
7
Q
What is DNA replication?
A
In order for growth and reproduction to occur, molecules of DNA must be duplicated to be passed on to new cells. This process is known as DNA replication.
8
Q
What is semi-conservative replication?
A
DNA replication is considered semi-conservative replication. The original double stranded molecule will divide into two parent strands. Each parent strand has a new strand
made. Each subsequent molecule is made up of one original and one new strand.
9
Q
What is the process of unwinding?
A
This process starts with the enzyme DNA helicase. DNA helicase unzips the long DNA molecule by breaking the hydrogen bonds between the nucleotides (A-T or G-C). The point after which the stands are separating is known as the replication fork.
10
Q
What is the role of DNA polymerase?
A
Inside the nucleus, there are stockpiles of spare nucleotides floating around. DNA polymerase (enzyme) is responsible for collecting these nucleotides and matching them with the complimentary pairs on the parent strand. DNA polymerase has a unique feature in that it can only synthesize in a 5’ to 3’ direction.
11
Q
DNA Strands:
A
As DNA is an antiparallel molecule, one strand synthesizes in the direction of unwinding and the other in the opposite direction. The strand that is replicating in the direction of unwinding is called the leading strand. This process is fairly straight forward as the bases are replaced shortly after unwinding. The strand replicating in the reverse direction is a little bit more complicated. This is known as the lagging strand.
12
Q
The lagging strand:
A
The lagging strand is replicated in small sections, with the polymerase enzyme constantly detaching and reattaching. In order for this to happen the stand needs to have a starting point to attach to. The enzyme primase, creates short segments of known as primers which bind to the lagging strand.
13
Q
What is a gene? (genetics definition)
A
The section of DNA responsible for a certain characteristic
14
Q
What is an allele? (genetics definition)
A
Alternative forms of the same gene
15
Q
What is a dominant allele?
A
The form of a gene that is expressed in a heterozygous individual. Represented by a capital letter (B).
16
Q
What is a recessive gene?
A
The form of a gene that is expressed in a heterozygous individual. Represented by a lowercase letter (b).
17
Q
Define genotype:
A
The combination of alleles that an individual has (Bb).
18
Q
Define phenotype:
A
The physical expression of the genotype.
19
Q
Define homozygous:
A
An individual with two of the same allele BB or bb.
20
Q
Define heterozygous:
A
An individual with two different alleles Bb.
21
Q
What does the polymerase enzyme do?
A
The polymerase enzyme then continues this primer to make up the section of DNA. These individual sections are name Okazaki fragments.
22
Q
What is DNA ligase?
A
Ligase is like a glue that seals the nucleotides together to make a long continuous strand.
23
Q
Process of DNA replication
A
- Helicase (enzyme) unwinds and unzips DNA molecule
- DNA polymerase adds nucleotides to the parent strand reading from 3’ end (of the parent strand) and moving towards the 5’ end (strand built 5’-3’)
- Leading strand building is continuous
- Lagging strand discontinuous
- Okazaki fragments formed
- DNA polymerase detaches and reattaches
- Primase creates primers for polymerase to bind to at the start of each Okazaki fragment
- Okazaki fragments are joined by DNA ligase
- DNA strands are then recoiled around the histones
24
Q
Steps of Mitosis:
A
Interphase:
* Cell growth
* Production of organelles
S (Synthesis)
* DNA replication
G2
* Produces proteins necessary for mitosis
25
Steps of Mitosis:
Interphase:
* Cell growth
* Production of organelles
* DNA replication
* Produces proteins necessary for mitosis
Prophase:
* Chromosomes condense and become visible
* Each chromosome comprises 2 chromatids
* Spindle fibres begin to form
* Nuclear membrane begins to break down
Metaphase
* Chromosomes line up along equator
Anaphase
* Spindle fibres attach to centromeres
* Spindle fibres pull chromatids to opposite poles of the cell
Telophase
* Chromatids group together
* 2 New nuclear membranes form
* Chromosomes unravel
* Cytokinesis occurs
26
Functions of Proteins:
1. Structures- ribosomes, chloroplasts etc
2. Transport across membranes
3. Communication – hormones
4. Cell metabolism- enzymes control chemical
reactions
5. Recognition- immune response
6. Movement- eg muscle cells
27
4 types of RNA:
1. Pre- mRNA
2. mRNA
3. tRNA
4. rRNA
* RNA is usually a single strand
* Uracil (U) replaces thymine (T)
28
What is Pre-mRNA?
Produced in the nucleus, must be altered by
enzymes, removing irrelevant sections
(introns) and leaving all the exons to produce
mRNA
29
What is mRNA?
Contains the code for the synthesis of specific
proteins. Each three base unit of mRNA is called a codon.
30
What is tRNA?
- Bring individual AAs to the mRNA for joining
into proteins
- Anticodon matches to complimentary mRNA codon
- Have a clover-leaf (or t) structure
- Each anticodon only carries one specific AA
31
What is rRNA?
Forms part of the structure of ribosomes. Not directly involved in the proteins synthesis
32
Process of transcription:
1. RNA polymerase makes DNA separate (template strand & coding strand)
2. RNA polymerase makes a copy of the DNA (pre-mRNA) by nucleotides joining to the template strand
3. DNA codes to stop
4. Methyl cap (5’) and poly A (3’) tail added
5. Introns are removed to leave exons only mRNA (splicing)
Methyl cap- signaling molecule for ribosome
Poly A tail- protects molecule from damage
33
Process of translation:
1. Ribosome joins to binding site of mRNA
2. Ribosome moves along mRNA (reading codons)
3. AUG (methionine) is the code to start making
protein
4. tRNA bring AAs to ribosome
5. tRNA anticodon binds to mRNA codon
6. AAs join together using energy from ATP
7. tRNA detaches
8. mRNA is read until it reaches a stop codon
34
What is meiosis?
A process where a single cell divides twice to produce four cells containing half the original amount of genetic information (gametes)
35
Meiosis differences from mitosis:
- The parent cell divides twice
- Four daughter cells are produced (instead of two)
- Chromosome number is halved (diploid cells divide to become haploid cells)
- The daughter cells are not genetically identical
36
Steps of Meiosis:
Prophase 1:
* Homologous chromosomes pair up
Metaphase 1:
* Homologous chromosomes line up along equator
Anaphase 1:
* Homologous chromosomes pulled to separate sides of cell
* Chromosome and copy go to one side
Telophase 1:
* 2 haploid cells form
Prophase 2:
* Spindle fibres form perpendicular to first set
Metaphase 2:
* Chromosomes line up along equator
* Perpendicular to first set
Anaphase 2:
* Chromosomes split at centromere
* Sister chromatids separate to opposite poles
Telophase 2:
* 4 haploid daughter cells form
37
Significant features of Meiosis:
* 2 successive divisions
* 1st division separates homologous chromosomes into separate cells
* 2nd division separates chromatids into separate cells
* 4 haploid daughter cells
* Each having half the number of chromosomes of parent
38
What is DNA profiling?
is a forensic technique used to compare the
base sequences of 2 or more individuals to
determine how similar they are. Uses Short Tandem Repeats (STRs)- sections of non-coding DNA that are repeated in the DNA. The number of times they repeat is unique to each individual therefore everyone has a unique DNA fingerprint.
39
Steps of DNA profiling (Genetic Fingerprinting):
1. Extract DNA from sample
2. STRs cut into sections using restriction enzymes
3. Amplified using PCR
4. Separate fragments using gel electrophoresis
40
Uses of DNA profiling:
* DNA identification
* Genetic fingerprinting
* Paternity tests
* Bloodlines of livestock
* Genetic screening for inherited diseases
* Monitoring biodiversity- wild & breeding
programmes
* Identifying diseases
41
Steps of Gel Electrophoresis:
1. DNA is cut up using different restriction enzymes (creates segments of different lengths)
2. Fluorescent dye is added to samples
3. Samples are added to the wells in the gel at the negative electrode end (including samples of a known size- ladder)
4. Electricity is run through the gel and the negatively charged DNA is attracted to the positive electrode (smallest fragments move the furthest)
5. DNA is viewed under UV light which causes it to fluoresce
** scientists estimate the size of the fragments by comparing them to the samples of known size (molecular size markers)
42
What is the Human Genome Project?
The human genome project was an international research project in which scientists from all around the world worked together to sequence the entire human genome. Despite finishing ahead of schedule the project took 13 years to complete.
43
What is DNA sequencing?
determining the order of the nitrogen bases that make up the DNA molecule.
44
DNA sequencing can be used for:
* Determining which stretches of DNA contains genes
* Determining which stretches carry regulatory instructions, turning genes on or off
* Identifying target genes for GMO
* Determining evolutionary relatedness
* Forensics
45
What are terminator bases?
Free nucleotides with an altered sugar that prevent them from forming longer chains. Each terminator base also has a fluorescent tag. When a laser shines on the tag it fluoresces and the colour is recorded.
46
Steps of DNA sequencing (The Sanger Method):
Step 1 - Denaturing the DNA: This is done by heating the strands up to 96oC.
Step 2 - Annealing the primer: Primers are added and the temperature is reduced to 50oC allow the primer to anneal to the single strands of DNA.
Step 3 - Synthesize strand: The temperature is then increased to 60oC to allow the polymerase enzyme to synthesise the complementary strand. Until a terminator base is in place.
Step 4 - Denatured: The temperature is then increased to 96oC to separate the synthesised DNA from the template
Step 5 - Cycles: Steps 1-4 are repeated
Step 6 - Gel Electrophoresis: Fragments separated by gel electrophoresis in a capillary tube. Attracted to positive electrode. Smallest fragments reach the end fastest.
Step 7 - Fluorescing: As the terminator bases pass through the end of the capillary tube they are hit by a laser that causes them to fluoresce. The colour is recorded by a computer. The colour tells us what base it is
47
What is a mutation?
A mutation is any change to the DNA
sequence. Mutations can occur spontaneously during cell DNA replication or can be induced by physical, chemical or biological agents called mutagens.
48
What is a mutagen?
A mutagen is a substance or factor that induces a higher than normal rate of mutation. They are put into 3 categories: Physical, Chemical and Biological.
49
Physical Mutagens:
Radiation that causes damage to DNA is considered to be a physical mutagen.
This includes things such as:
- UV light: Exposure to ultraviolet light can cause distortions in the double helix. Can lead to more errors in replication or the inability for enzymes to bind. These mutations are what lead to skin cancer.
- X-rays: X-rays and nuclear radiation are capable of breaking or severing DNA strands. These broken strands are sometimes transcribed into dangerous or inactive proteins. They could also be repaired incorrectly, again leading to mutated DNA.
- Nuclear radiation: Breaks in DNA strands
50
Chemical Mutagens:
The process involves a substitution of
bases with other chemicals or the
attachment of chemical markers to DNA
strands. This can cause replication errors, prevent transcription occurring or enabling the transcription of different proteins.
51
Biological Mutagens:
Some mutations are caused by the action of invasive pathogens such as bacteria and viruses. Some of these pathogens actually integrate their DNA with their host, meaning all future cells show genetic mutation.
52
Types of mutations:
A mutation with no effect on the coded product is considered a neutral mutation.
Some mutations are considered Deleterious mutations. These can either stop or alter the production of proteins.
Few mutations are beneficial and lead to the advantageous variation that allows species to evolve.
53
Mutations in somatic cells:
Mutations can occur in somatic cells or germ line cells (body or sex). If in a body cell, only subsequent cells will be affected. If in a germ line cell, the entirety of the next organisms cells will have that mutation.
54
Point Mutation:
Point mutations refer to a change in DNA
where only one nucleotide is altered. Within point mutations there are several different categories including: Substitution, insertion and deletion.
55
What is substitution?
A substitution mutation occurs when one nucleotide is replaced by another. Substitution mutations are protected against due to the redundancy of the genetic code. That is, a changed codon might code for the same amino acid anyway so there is no difference. When this happens it is known as a neutral/silent/synonymous mutation.
56
How substitution mutation codes:
If the substitution mutation ends up coding for:
1. The same AA = neutral mutation
2. different AA = missense mutation
3. New stop codon = nonsense mutation
57
What is insertion and deletion?
Insertion: An extra base is added into the sequence
Deletion: A base is removed from the sequence.
These mutations result in a change in the codons following the mutation and are known as frameshift mutations.
58
Chromosomal variation:
Mutations can also happen on a larger scale
with changes happening to sections of
chromosomes. This can happen naturally during meiosis as the chromosomes tangle around each other, or because of mutagens that damage the chromosomes.
59
Chromosomal deletion:
If a strand is broken in two places, it is possible that the middle segment drops out and the other sections rejoin. This removes all of the genes from the middle section and can have a profound effect on the organism. This process is known as chromosomal deletion.
60
Chromosomal inversion:
A chromosomal inversion is the process where the middle section of a broken chromosome turns itself upside down before rejoining the other segments. The current understanding is that chromosomal inversion has no major health risks to humans although it has been linked to a decrease in fertility.
61
Chromosomal duplication:
Chromosomal duplication is the replication and insertion of a section of chromosome into an already existing chromosome.
62
Translocation:
Sometimes a section of chromosome will break off and attach to another chromosome. This process is known as translocation.
63
Polymerase Chain Reaction:
Sometimes there is not enough DNA to test. An enzyme called DNA polymerase is used to
produce duplicates. Original DNA fragment is split and copies made. Each time this process takes place the number of DNA fragments doubles. The DNA is amplified to create millions of fragments.
64
Small amounts of DNA:
* Crime scenes- body fluids, skin cells
* Preserved extinct animals
* Detecting viruses early
* Genetic screening
65
Steps of PCR:
- Denaturing: Heat to 95oC. DNA separates into 2 complimentary strands
- Annealing or hybridisation: Primers are added (forward and reverse). Primers are short (18-30 nucleotides) complimentary base sequences at the start and end of the coding section. Cooling 50-60oC causes primers to bind to single strand DNA. Primers bind before the complimentary DNA strands because there are many more of them
- Synthesis or primer extension: DNA polymerase added (Taq polymerase) as well as free nucleotides and heated to 72oC (incubated). DNA polymerase binds free nucleotides together to make new section of DNA (3’→5’ of template strand).
66
What are transgenic organisms?
Organisms that have had the DNA of a different species inserted into their genome
67
What are genetically modified organisms?
Organisms that have had their DNA modified. May be transgenic. May have had genes turned on/off
68
What are restriction enzymes?
Enzymes taken from bacteria. Cut DNA at recognition site (4-8 base pairs). In bacteria they cut up the DNA of invading viruses to destroy them. Scientists use them to cut DNA at recognition sites to remove a section of DNA.
69
What are sticky ends?
They have overhanging ends (sticky out bits). Can be joined to other DNA fragments with complimentary sticky ends. Sticky ends ensure that the DNA is inserted the correct way
70
What are blunt ends?
Cuts DNA straight across. No overhanging ends. Can be joined to any DNA with blunt ends. Blunt ends mean that the DNA could be inserted backwards, producing the wrong protein
71
What is the process of ligation?
Enzyme (DNA ligase) joins (splices) DNA strands together. Complimentary sticky ends. Any blunt ends. Produces recombinant DNA
72
Structure of Bacteria:
Plasmid: Small circular DNA, can replicate independently of the chromosomal DNA, Produce enzymes to disable antibiotics
73
Steps of creating transgenic organisms:
1. Detergent breaks down cell and nuclear membrane to release DNA
2. Ethyl alcohol makes DNA precipitate which is then collected
3. Isolate (cut out) the gene of interest-restriction enzymes
4. Use same enzyme to cut bacterial plasmid
5. Insert gene into plasmid (ligase)
6. Insert plasmid into bacteria (CaCl2, heat shock, electroporation)
7. Bacteria is cloned to produce large numbers
8. Cloned bacteria will express the inserted gene (ie make a particular protein- enzyme)
74
Uses of bacteria with recombinant DNA:
Production of:
* Insulin (pigs or cows)
* Chymosin (from calves)
* HGH- pituitary gland of cadavers
* Vaccine antigens
* Blood clotting factor (blood donors)
75
GMO'S:
Sometimes a gene will be inserted into a bacteria or virus which can then be inserted into a plant or animal in the hope that the gene will be incorporated into the host DNA and then be expressed in the host.
1. DNA is inserted into vector (bacteria or virus)
2. Vectors are introduced to the host cells
3. Host cells incorporate Recombinant DNA with their own DNA
76
Use of Transgenic organisms:
* Alternative to pesticides and herbicides
* Prevent breeding of vectors ie mosquitoes
* Control feral animals
* Processing oils and toxic wastes – bacteria
* Disease resistant crops
* Vaccines
77
What desirable traits have GMO's been engineered for?
1. resistance
2. faster growth rate
3. greater product quality and yield
4. tolerance to adverse environmental conditions
78
What are the potential benefits of GMO's in agriculture?
* Improved crop productivity
* Improved nutritional value
* Better flavour
* Fresher produce (longer shelf life)
* Less pesticide, herbicide residue on food and in environment
79
DNA profiling in terms of monitoring endangered species:
*DNA profiling allows ecologists to map the gene pool of an endangered population
*Viable gene pool- used to determine the biodiversity of the population and how vulnerable to extinction or resilient to change the population may be
* Can then protect or intervene
* Mapping of a genome may allow scientists to: determine susceptibility of individuals to disease, may aid the development of vaccines for diseases
80
Assessing gene pools for breeding programs:
* DNA profiling allows zoos to introduce individuals in to their breeding programs to increase the biodiversity (minimise in-breeding)
* Avoid breeding individuals with genetic disorders
* Breed individuals with favourable characteristics
* When introduced to the wild the increase in biodiversity will make the wild population more resilient to change
81
Tracking changing biodiversity:
Information can be gathered to track the change of genetic biodiversity at the species level as well as at the ecosystem level. May help to understand changing selection pressures in ecosystems
82
DNA profiling in terms of quarantine:
Infected organisms may be isolated until they are clear of infectious organisms. DNA profiling allows quarantine officers to determine whether imported goods are from illegal sources. Can be used to determine whether animals were bred in captivity or the wild
