6.1 Cellular control Flashcards
(114 cards)
1
Q
What is a mutation?
A
Change to the genetic material.
2
Q
What do muations include?
A
Changes to the structure or number of chromosomes.
3
Q
When do most mutations occur?
A
Before cell division/ interphase.
4
Q
What can cause mutations?
A
- Tar in tobaocco smoke
- Ionising radiation such as UV light, xrays and gamma rays.
-> These may contain chemicals that are mutagenic.
5
Q
What are somatic mutations?
A
Mutations associated with mitotic divsions.
6
Q
What are the charateristics of miotic divisions?
A
They’re not passed onto their offspring and can be associated with cancerouks tumours.
7
Q
What are he characteristics of a mutation associates with mieosis?
A
Mutaion in gamete formation and will be inherited by offspring.
8
Q
What are the main 2 classes of DNA mutation?
A
- Point mutation
- Insersion or deletion
9
Q
What is a point mutation?
A
One base replaces another.
10
Q
What is a insersion or deletion mutation?
A
One or more nucleotides are inserted or deleted from a length of DNA. These may cause a frameshift.
11
Q
What are rhe 3 types of point mutation?
A
- Silent
- Missence
- Nonsence
12
Q
What does it mean that DNA is degenerate?
A
t
There are many instances in which different codons specify the same amino acid.
13
Q
What characteristic of DNA means a mutation does always lead to a change of the sequence of amino acids in a protein?
A
DNA is degenerate
14
Q
What is a silent mutation?
A
A type of point mutation involving a change to the base triplet where that triplet still codes for the same amino acid.
15
Q
What is a missense mutation?
A
A point mutation which leads to a change to the base triplet sequence that leads to a change in the amino acid sequence in a protein.
16
Q
What is the effect of a missence mutation?
A
THere can have a significant effect on the protein being produced as it is altering the primary structure leading to a change on the teritary structure and its function.
Hiwever, the change to it’s tertiary structure may be in an area that does effect it’s function so could be insignificant.
17
Q
What condition is caused by a missence mutation?
A
Sickle cell amaenia results from a missence mutation on thr 6th base triplet of the gene B-polypeptide chains for haemoglobin.
18
Q
What is a nonsence mutaion?
A
A point mutation that alters a base triplet so that it becomes a termination triplet.
19
Q
What is the result of a nonsence mutation?
A
It results in a truncated protein that will not function. This abnormal protein will most likely be degraded within the cell.
20
Q
What is an indel mutation?
A
Insertion and deletion mutations
21
Q
What is the result of an indel mutation (not in multiples of 3)?
A
Because the cose is non-overlapping, all the subsequent base triplets are altered. This is a frameshift. THis will sevely alter the primary structure, the tertiary structure and therfore, it will not be able to carry out it’s function. The protein will be degraded within the cell.
22
Q
What condition is a result of an indel mutation?
A
Thalassaemia, a haemoglobin disorder, results from a frame shift due to deletions of nucleotide bases.
23
Q
When would indel muations not be very dissruptive?
A
With insertions or deletions of a triplet of base pairs result in the addition or loss of an amino acid- this is not a frameshift.
24
Q
What happens is an expanding triple nuceotide repeat?
A
This is a type of indel mutation, the number of CAG triplets increases at meiosis and again from generation from generation.
25
What condition is a result from an expanding triple nuceotide repeat?
Huntington disease. If the number of CAG sequences goes above a certain critiacl number then the person with that genotype will develop the sympotoms of Huntingtons disease later on in life.
26
When have mutations been benificial?
They've helped drive evolution through natural selection.
27
What a some examples of mutations that appear to be neutral, neither benificial or negative?
* Inability to smell certain flowers
* Differently shaped earlobes.
28
What is an exon?
The coding, or expressed, reigon of DNA
29
What is an intron?
The nonb-coding region of DNA.
30
What is operon?
A group of genes that function as a single transcription unit; first identified in prokaryote cells.
31
What is a transcription factor?
Protein or non-coding RNA that can combine with a specific site on the length of DNA and inhbit or activate trascription of the gene.
32
What does E.coli normally respire?
Glucose
33
What will E.coli respire if glucose isnt available?
Lacose
34
What enzymes does the presence of lactose in E.coli produce?
* Lactose permease
* B-galactosidase
35
What is the lac operon? What does it contain?
A length of DNA, about 6000 base pairs long, containing lacO next to structural genes lacZ and lacY that cose for the enzymes lactose permease and B-galactosidase.
36
What does lactose permease do?
Make the bacteria E.coli nore permeable to lactose.
37
What does B-galactosidase do?
Hydrolyses lacose to glucose and galactose.
38
Which reigion does RNA polymerase bind to on the lac operon to allow the trascription of the structural genes lacZ and lacY?
The promoter region.
39
What does the regulatory gene on the lac operon code for?
A repressor protein (lacI)
40
What occurs in the lac operon in E.coli in the presence of glucose?
* The regulatory gene codes for a repressor protein.
* When this protein is expressed, it will bind to the operator, preventing RNA from binding to the promoter reigion.
* The repressor reigion therefore prevents the genes lacZ and lacY.
41
What are the control sites on the lac operon?
* Promotor reigion
* Operator
42
What are the structural genes o the lac operon?
* LacZ
* lacY
43
What is the advantage to E.coli having a lac operon system to induce the formation of enzymes to metabolise lactose?
The presence of a lac operon system means energy and amino cids aren't wasted on producing enzymes when they're not needed.
44
What occurs in the lac operon in E.coli in the presence of lacose?
* The regulatory gene expressed the repressor protein, however, lactose will act as an inducer and lacose will will bind to the repressor protein.
* This alters the shape of the repressor protein, preventing it from binding to the operator.
* The RNA polymerase can then binf to the promoter reigion and begin transcribing the structural genes into MRNA that will then be translated into lactse permease and B-galactoside.
45
In the lac-operon system, which molecule is the inducer?
Lacose- lacose induces the enzymes needed to break it down.
46
What does every cell in a eukaryote have in common?
All eukaryote cells have the same genome. All these cells express the basic 'housekeeping' genes.
47
What are transcription factors?
They are proteins, or short non-coding pieces of RNA, that act within the cell's nuceus to control which genes in a cell are turned on or off.
48
Why are do eukaryotes have different cells as they have the same genome?
Certain genes are expressed in different cells.
49
What do transcription factors do?
They slide along a part of the DNA molecule, seeking and binding to their specific promoter regions. They then aid or inhibit the attatchment of RNA polymerase to the DNA.
50
What are transcription factors essential for?
**Regulation of gene expression in eukaryotes**, making sure that different genes in different types of cells are activated or supressed.
51
What are certain tarnscription factors involved with?
Some are **involved with regulating the cell cycle**. Tumour suppressor genes and proto-oncogenes help regulate cell division v ia transcription factors. Mutations to these can lead to uncontrolled cell division or cancer.
52
How much of genes in the human genome aproximatley encode for transcription factors?
About 8%
53
Why is it not significant that a promotor region might/ be some distance away along a wound length of DNA?
Because of how the DNA can bend, the promoter region may not be too far away spatially.
54
Why is it essential for the regulation of gene expression in eukaryotes?
To make sure different genes are acivated or supressed.
55
What transcription factors help regulate the cell cycle?
Tumour suppressor genes and proto-oncogenes.
56
What percentage of the human genome encode transcription factors?
About 8%
57
What are the different regions within a gene called?
Introns and exons.
Introns are non-coding regions while exons are coding regions within the gene.
58
Describe how DNA in a gene is transcribed with regards to introns and exons?
All the DNA, both introns and exons are transcribed. The resulting mRNA is callled **primary mRNA**. Primary mRNA is then edited and the RNA introns are removed. The remaining mRNA exons are joined together to form mRNA. **Endunuclease enzymes** may be involved in the editting and splicing process.
59
What enzyme is involved in the editing and splicing of primary mRNA?
Endonuclease enzyme
60
What do introns do?
Some introns encode proteins, and some may be short non-coding lengths of RNA involved in gene regulation.
61
After primary mRNA is spliced, how many proteins can it encode for?
Can encode for one or more than one protein.
62
What is post-transcriptional gene regulation?
When a transcribed length of primary mRNA is edited and spliced to produce mRNA.
63
What does post translational level of gene regulation involve?
It involves the acitvatin of proteins.
64
What does ATP become when catalysed by adenyl cyclase?
cAMP
65
How does cAMP activate enzymes and stimulate transcription?
1. A signaling molecule, such as the protein hormone glucagon, binds to a receptor on the plasma membrane on the target cell.
2. This activates a transmembrane protein which then activates adenyl cyclase enzymes.
3. The activated G protein activates activates a G protein.
4. Adenyl cyclase enzymes catalyse the formation of many molecules of cAMP from ATP.
5. cAMP activates PKA (protein kinase A)
6. Activatedx PKA catalyses the phosphorylation of various proteins, hydrolysing ATP in the process. This phosphorylation activates many enzzymes in the cytoplasm.
7. PKA may also phosphorylate another protein.
8. This then enters the nucleus and acts as a transcription factor, to regulate transcription.
66
What happens in step 1?
A signalling molecule, such as a protein hormone, binds to a eceptor on the plasma membrane of the target.
67
What happens in step 2?
A transmembrane prootein is activated which then activates a G protein.
68
What happens in step 3?
The activated G protein activated adenyl cyclase enzymes.
69
What happens in step 4?
Activated adenyl cyclase ezymes catalyse the formation of many molecules of cAMP from ATP.
70
What happens in step 5?
cAMP acrtives PKA (protein kinase A)
71
What happens in step 6?
Activated PKA catalyses the phosphorylationn of various proteins, hydrolysing ATP in the process. This phosphorylation activates many enzymes in the cytoplasm, for example those that convert gylcogen to glucose.
72
What happens in step 7?
PKA may phosphorylate another protein (CREB, cAMP responce element binding).
73
What happens in step 8?
This then enters the nucleus and acts as a transcfription factor, to regulate transcription.
74
What is apoptosis?
programmed cell death.
75
What is the homeobox sequence?
Sequence of 180 base pairs (excluding introns) found within genes that are involved in regulating patterns of anatomical developmeant in animals, fungi and plants.
76
What are hox genes?
Subset of homeobox genes, found only in animals; involved in formation of anatomical features in correct locations of the body plan.
77
How old are homeotic genes?
Ancient
78
What are homeotic genes in control of?
Anotomical development/ morphogenesis so that all the structures develop in the correct loacation.
79
What do hemeotic genes contain?
Homeobox sequences/ Homeobox genes
80
How long is a homeobox sequence and what does it code for?
Each homeobox sequence is a stretch of **180 DNA base pairs** (excluding introns) encoding for **60 amino-acid sequence**, called the **homeodomain sequence**, within a protein.
81
The homeodomain sequence folds into a particular shape, what does this allow it to do?
Allows it to bind to DNA, regulating the transcription of adjacent genes.
82
What does the homeobox sequence code for?
A protein that acts as transcription favtors and act within the cell nucleus.
83
What is the shape of the homeodomain-containing proteins called?
The shape of the homeodomain-containing proteins is called H-T-H. It consists of two α helices (H) connected by one turn (T).
84
What is an enhancer region?
A region that initiates or enhances transcription.
85
What does the homedomain amino acid sequence do?
It recognises the TAAT sequence of the enhancer region of a gene to be transcribed.
86
What are homeobox sequence crucial for?
The homeboc sequence is crutial for the regulation od development and diffrentiation in organisms.
87
In what organisms are hox genes found?
Only found in animals.
88
What organisms have homeobox genes in?
Animals plants and fungi
89
What are the characteristics of homeobox gene sequences?
* They're very similar in different organims
* Highly conserved
90
How do Hox genes regulaate the development of embryos?
Hox genes regulate the development of embryos along the anterior-posterior (head-tail) axis.
91
What can occur if a Hox gene is mutated?
If Hox genes are mutated, abnormalities can occur such as the antennae of the head
91
What can occur if a Hox gene is mutated?
If Hox genes are mutated, abnormalities can occur such as the antennae of the head
92
What can occur if a Hox gene is mutated?
If Hox genes are mutated, abnormalities can occur such as the antennae of the head on the head of Drosphila (fruit fly) developing as legs, or mammalian eyes develping on limbs.
93
How are hox genes arranged?
Hox genes are arranged in clusters and each cluster may congain up to 10 genes.
94
What is a terapod?
4 limbed vertebrates, inclduing mammmals
95
In what order are hox genes expressed in embryos?
In order along the **anterior-prosterior** axis of the developing embryo. The **sequential and temporal order** of the gene expressions corresponds to the sequential and temporal development of various body parts, a phenomenon known as **colinearlity**.
96
What is the phenomenon of colinearity reffereing to the order in which hox genes are expressed in embroys?
The phenomenon that the genes are expressed in **sequential and temporal order**.
97
What can the homeodomain proteins do in the nucleus?
They act as transcription factors which:
* Switch on cascades of acitvation of other genes that promote miotic cell division.
* Apotosis
* Cell migration
* Regulate the cell cycle
98
How are hox cells regulated?
Hox genes are regulated by other genes called **gap genes and pair-rule genes**. In turn, these genes are regulated by msternslly suplied mRNA from the egg cytoplasm.
99
How do Hox genes regulate the cell cycle during miotic divisions?
It ensures that each new daughter cell contains the full genome and is a clone of the parent cell.
100
How is aptosis different from cell death due to trauma? e.g. Necrosis
Cell death due to trauma involved hydrolic enzymes and therefore in more destrictive than aptosis which is more controlled.
101
What sequence of events occur in apoptosis?
1. Enzymes break down the cell cytoplasm.
2. The cytoplasm becomes dense with tightly packed organelles.
3. The cell surface membrane changes and small protusions called blebs form.
4. Chromatin condenses, the nuclear envolope breaks down and DNA breaks into fragments.
5. The cell breaks into vesicles that are ingested by phagocitic cells, so that cell debris does not damage any other cell tissues. The whole process happens very quickly.
102
Whats happening in step 1 and 2 of aptosis?
Enzymes break down the cell cytoskeleton. The cytoplasm becomes dense with tightly packed organelles.
103
Whats happening in step 3 of aptosis?
The cell surface membrane changes and small prtrusions called blebs form.
104
What happens in step 4 of aptosis?
Chromatin condenses, the nuclear envolpe breaks down and DNA breaks into fragments.
105
Whats happening in step 5 of aptosis?
The cell breaks down into vesicles that are ingested by phagocytic cells, so that debris does not damage any other cells or tissues.
106
What cell molecules arereleased to regulate aptosis?
* Cytokines (from immune system)
* Hormones
* Growth fators
* Nitric oxide
107
How can nitric oxide regulate aptosis?
Nitric acid can induce aptosis by making the inner mitochondrial membrane more permeable to hydrogen ions and dissipating the proton gradient. Proteins are released into the cytoplasm where they bind to aptosis inhibitor proteins, allowing aptosis to occur.
108
What are some uses of aptosis?
* During limb development, aptosis causes digits to separate from each other.
* Aptosis removes ineffective or harmful Y-lymophocytes during the development of the immune system.
109
How many cells in a child go through aptosis every day?
20-30 billion.
110
How many cells in an adult go through aptosis every day?
About 50-70 million.
111
What should the rate of cells dying of aptosis be equal to?
Should be equal to the rate of cells being produced by mitosis.
112
What does not enough aptosis lead to?
Leads to formation to tumours.
113
What does too much aptosis lead to?
Leads to cell loss and degeneration.
