Cell Division, Differentiation, Development & Inheritence Flashcards
(100 cards)
1
Q
What happens in the S phase of the cell cycle?
A
DNA replication.
2
Q
What happens in the G1 phase of the cell cycle?
A
Cells that do not divide are arrested here and sent to G0.
3
Q
What happens in the M phase of the cell cycle?
A
Mitosis and cytokinesis.
4
Q
What are the 2 main parts of the cell cycle?
A
Interphase (G1, S and G2) and M phase (mitosis and cytokinesis).
5
Q
What are cyclin-dependant kinases CDK’s and what are they regulated by?
A
Protein kinases that are the ‘engines’ of the cell cycle. The activity of these is regulated by cyclins. There are 4 types of mammalian CDK. Different cyclins bind to different CDK’s. The cyclin must be present for the CDK to bind to it and work. Different cyclins accumulate and are destroyed at different points of the cycle controlling when the CDK’s are active in the cell cycle.
6
Q
At what points in the cycle does the cell undergo checks and what do they do?
A
- End of G1 - checks for cell size and favourable environmental conditions. Checks for DNA damage. Restriction point here.
- During G2 - Check for damaged or unduplicated DNA. Check for unduplicated chromosomes.
- End of M - Check for chromosome attachment to mitotic spindle.
7
Q
Why might a cell divide uncontrollably and cause a tumour?
A
If a cell becomes defective in the signalling machinery it might enter the cell cycle permanently and give rise to identically defective daughter cells.
8
Q
What are the 4 main ways cancer drugs can target the cell cycle?
A
- Drugs such as taxol work in the M phase to block the mitotic spindle.
- Drugs such as etoposide work in the G1 phase to inhibit growth factor stimulation at the restriction point.
- Drugs such as 5-flurouracil work in the S phase to block DNA damage.
- Radiation can damage DNA and cause apoptosis at the S and G2 checkpoints.
9
Q
What are nucleosomes?
A
DNA tightly packed and wrapped around histones.
10
Q
What happens to the nucleosome prior to mitosis?
A
They become supercoiled (even tighter wrapped) to make it inaccessible to proteins involved in replication and transcription.
11
Q
What is the role of the mitotic spindle in mitosis?
A
Mediates the segregation of chromosomes. The condensed chromosomes attach to the microtubules which radiate from the 2 centrosomes.
12
Q
What happens in prophase?
A
Chromatin supercoils to condense into visible chromosomes consisting of identical, paired sister chromatids. The centrosomes move to opposite poles.
13
Q
What happens in prometaphase?
A
The nuclear envelope breaks down. Kinetochore microtubules appear and connect the kinetochores to the poles.
14
Q
What happens during metaphase?
A
The centrosomes become aligned in a plane at the cells equator.
15
Q
What happens during anaphase?
A
The paired chromatids separate and the new daughter chromosomes move towards the poles.
16
Q
What happens during telephase?
A
The daughter chromosomes reach the poles. The nuclear envelopes and nuclei reform, the chromatin decondenses. Cytokinesis follows and the daughter cells then enter interphase again.
17
Q
What is cytokinesis driven by in animal cells?
A
The contraction of an actin-myosin ring.
18
Q
What is cytokinesis driven by in plant cells?
A
Construction of a new cell wall inside the cell.
19
Q
What is cell necrosis?
A
Cell death caused by cell-damaging agents or oxygen/nutrient starvation. Does not require energy. Symptoms include cell swelling and cell lysis. Generates an inflammatory response.
20
Q
What are the characteristic morphological features of apoptosis?
A
Cell condensation, membrane blobbing, nuclear shrinkage, chromatin condensation and fragmentation, and formation of apoptotic bodies. Cell contents are not released, DNA and proteins are broken down. Does not cause inflammatory response.
21
Q
Why is apoptosis as essential as cell division?
A
Because it regulates cell numbers by balancing cell division. Important for developmental processes and removal of pathogenic cells (e.g. virus infected cells, immune cells, cells with DNA damage). Also needed in the developing CNS because there is insufficient neurotrophic to support all the neurons produced though cell division.
22
Q
What are the 2 cell death genes that cause apoptosis and the gene that prevents apoptosis?
A
Causes apoptosis - Ced-3 = caspase, and Ced-4 = Apaf 1.
Prevents apoptosis - Ced-9 = Bcl-2.
23
Q
What does the ced-3 gene do?
A
Ced-3 produces cysteine proteases (caspases) that are present in the cytoplasm and mitochondria. They are inhibited by IAP proteins and need to be cleaved to become active. They cleave after an aspartic acid residue.
24
Q
What are the 2 distinct classes of caspases?
A
- Initiator caspases (8, 9, 10) - activated by pro-apoptotic stimuli. Cleave and activate executer caspases.
- Executer caspases (3, 6, 7) - Activated by initiator caspases. Cleave a variety of target proteins resulting in execution of apoptosis.
25
What are the 2 things caspases can be activated by?
Death receptor pathway and intrinsic pathway.
26
What is the role of mitochondria and Bcl-2?
Opening of pores in the mitochondrial outer membrane triggers cytochrome C release and caspase activation. Bcl-2 prevents the formation of pores in the outer membrane so the cell must overcome Bcl-2 to activate programmed cell death pathway.
27
What are stem cells?
Undifferentiated quiescent (slow-cycling) cells that undergo cell division when activated (e.g. after injury).They have the capacity for self-renewal through asymmetric cell division and the capacity to differentiate into mature cells (potency).
28
What is the meaning of totipotency, pluripotent and multipotency?
Totipotency - Can give rise to all embryonic and extra-embryonic cell types.
Pluripotency - Gives rise to all cell types found in adult organism.
Multipotency - Gives rise to multiple but not all cell types in the adult organism.
29
How does differentiation work?
Cells switch on certain genes and switch off others. So the type of cell formed is determined by the pattern of gene expression in the cell.
30
What is the role of transcription factors in differentiation?
Specific transcription factors called master regulators are expressed at an early stage in the differentiation process and they induce (or suppress) transcription of various target genes that collectively lead to cell differentiation.
31
What is MyoD in muscle for?
To mediate the shutting down of cell division for differentiation to occur through up regulation of the cell cycle inhibitor p21.
32
What is determination?
Before differentiation occurs, the fate of the cell is determined. Determination does not show in an outward phenotype.
33
What 2 main mechanisms determine cell fate in differentiation?
1. Cytoplasmic segregation (asymmetric cell division) - cytoplasmic determinants that are unequally distributed between daughter cells influence cell fate.
2. Induction - Factors that are secreted by neighbouring cells influence cell fate.
34
What are cytoplasmic determinants (cell differentiation)?
Agents differentially inherited at each cell division that make cells different from each other.
35
What are inducers (cell differentiation)?
Extracellular molecules to which the cell is exposed. A high concentration may activate a transcription factor that triggers the cascade of cellular differentiation.
36
Is determination (differentiation) reversible?
In the early embryo yes, by changes in the environment. Not possible in later stage embryo's however.
37
Is cell differentiation reversible?
Mature plant cells can be induced to dedifferentiate to a totipotent state in a process called cloning.
38
What are the 2 types of technology available to reprogram mammalian somatic cells into pluripotent/totipotent stem cells?
Somatic cell nuclear transfer (cloning) and induced pluripotent stem cells (iPSCs).
39
What does genomic equivalence meaning (cloning)?
No information is lost from the nuclei of cells as they differentiate into mature somatic cells during cloning.
40
what are choanoflagellates?
Close relatives to animals. Unicellular eukaryotes that form colonies during part of their life cycle. Information from genome projects indicates they are the closest known unicellular living relatives of animals.
41
What are the 2 steps of becoming a multicellular organism?
1. Colony formation - cells stuck together consisting of identical cells.
2. True multicellular organism - Selective cell adhesion, cells have different properties and is composed of genetically identical cells.
42
What is a possible driving force for colonies?
Predation. The alga, chlorella vulgarisms normally grows as single cells but in response to the presence of a predatory eukaryote it develops into stable colonies which are almost immune to predation.
43
What are 'cheater cells' (colonies)?
Cells that can exploit the 'altruism' of other in the colony.
44
Why are volvox true multicellular organisms but Gonium is not?
Gonium only produces identical cells, whereas Volvox can differentiate into distinct cell types and has developed a mechanism for sexual reproduction through production of eggs and sperm.
45
What does morphogenesis mean?
Coordinates the basic cellular processes to cause an organism to develop its shape.
46
What are the 3 main body axes of vertebrates?
Dorsal-ventral, Anterior-posterior and Left-right.
47
Inducers form a concentration gradient. What are inducers that directly affect target cells in a concentration-dependent manner called?
Morphogens.
48
What are morphogen gradients established by?
Signalling centres. Multiple signalling centres can act in concert to provide positional information along all 3 body axes.
49
What does the egg give to the embryo and what does the sperm give?
Egg - Half of nuclear DNA and cytoplasm (organelles, nutrients, mRNA, proteins).
Sperm - Half of nuclear DNA and the centriole.
50
What is cleavage (embryonic cell divisions)?
Early cell divisions that are rapid and don't increase overall size of developing embryo. Involves a modified cell cycle of S and M phases without the gap phases, driven by high cyclin-CDK activity. Results in the formation of the blastula.
51
What does the slow, asynchronous cleavage in mammals result in the formation of?
A blastocyst. This will form the embryo, contribute to the placenta and umbilical cord and contains factors for cellular differentiation.
52
What is there gastrulation process (developmental)?
The blastula is transformed into an embryo with distinct tissue layers and body axes (the germ layers are developed).
53
What are the 3 germ layers?
Ectoderm (outer), mesoderm (intermediate) and endoderm (inner).
54
What does epiboly mean?
The flattening and extension of cells that occurs on the outside of the blastula.
55
What does convergent extension mean?
The intercalation of cells in the direction of movement that directs involution (moving inward).
56
How is the grey crescent created and what is it required for?
Fertilisation triggers a rotation of the cortical cytoplasm that leads to the formation of the grey crescent. Experiments show the grey crescent is required for gastrulation.
57
How is the organiser (dorsal lip) established?
Fertilisation induces a dorsal enrichment of B-catenin.
58
What is B-catenin?
A transcription factor that initiates a complex signalling cascade that leads to expression of the transcription factor, Goosecoid which activates organiser genes.
59
What is organogenesis?
The formation of organs and organ systems.
60
What happens during the process of neurulation?
The ectoderm caves in and folds over to create a tube that runs dorsally from the anterior to posterior end of the embryo. This initiates the formation of the nervous system.
61
What are somites and what does the formation of them induce?
Segments of mesodermal tissue that form along the length of the neural tube. Induces body segmentation.
62
What are hox genes?
A group of related genes that control the body plan of an embryo along the anterior-posterior axis. The order of them on the DNA mimic their temporal and spatial expression along the anterior-posterior axis of the developing organism. They ensure the right body parts develop in the right place.
63
What are the 3 tissue layers in plants?
Dermal, ground and vascular.
64
What are meristems (plants)?
Regions containing undifferentiated cells that will continue to give rise to new tissues and orchestrate growth throughout life.
65
What is the first law of inheritance?
The law of segregation. During production of gametes the 2 copies of each gene segregate and each gamete receives only one copy. The zygote recipes a copy of the gene from each parent. Alleles can be dominant or recessive.
66
What does polymorphic mean?
A gene with more than 1 allele.
67
What is a monogenic condition?
A disease caused by one single gene.
68
What is the second law of inheritence?
The law of independent assortment. The alleles of different genes can be divided across the gametes independent of each other. This leads to parental traits appearing in new combinations in some of the offspring. This law generally only applies to genes that are on separate chromosomes.
69
What are the exceptions to Mendels laws?
- Multiple alleles of a gene can exist and produce a range of phenotypes (not always just 2 alleles).
- Incomplete dominance where neither of the 2 alleles is dominant.
- Co-dominance where alleles produce phenotypes that both appear in heterozygotes.
- Pleiotropic allele where one allele has multiple phenotypic effects.
- Epistasis where one gene alters the phenotypic expression of another gene.
70
What is the ABO blood type controlled by/what are the alleles?
The ABO gene which has 3 alleles: IA, IB and I. IA and IB are co-dominant over I.
71
The ABO gene encodes a glycosyltransferase. But what does each enzyme encoded by the IA, IB and I allele add?
IA allele enzyme adds an N-acetylgalactosamine to the H antigen.
IB allele enzyme adds a galactose
I allele enzyme is inactive.
72
What gene controlled the presence/absence of the AB antigens on the RBC membrane?
The FUT1 gene which has 2 alleles: H and h.
73
What does the FUT1 gene encode and what do the enzymes encoded by the alleles?
A fucosyltransferase. The enzyme encoded by the H allele adds a fructose to precursor substance. The enzyme encoded by the h allele is inactive.
74
What is the Bombay phenotype?
People who are homozygous for the FUT 1 h allele so cannot produce the H antigen regardless of ABO genotype. The RBC's do not express any of the ABH antigens on the cell surface. These individuals have antibodies against A, B and H antigens so can only receive blood from others who have the Bombay phenotype.
75
What are polygenic traits?
A characteristic that is determined by many genes such as height. Environment can have an impact.
76
What 2 processes introduce variation?
1. Mutation - a heritable change in the genetic information of a cell.
2. Recombination - The rearrangement of genetic materials that happens during sexual reproduction.
Without these processes, there would be no evolution.
77
What can spontaneous mutations be caused by?
Chemical reaction that alter nucleotides, errors in DNA replication, errors during mitosis.
78
What can induced mutations (caused by mutagens) be caused by?
Damaging chemicals or ionising/UV radiation.
79
What happens in a silent point mutation?
A nucleotide change that does not alter the amino acid sequence of the protein (synonymous mutations).
80
What happens in a missense point mutation?
Changes a codon into one that specifies a different amino acid, affecting the amino acid sequence of the protein.
81
What happens in a nonsense point mutation?
A codon that specifies an amino acid into a stop codon, terminating translation prematurely.
82
What is a frame-shift point mutation?
Insertion or deletion of one or 2 bases which will alter the reading frame of the entire DNA sequence from that point onwards, resulting in all the amino acids being changed after the point of insertion.
83
How can a chromosomal mutation be silent?
- Occurs in a non-coding region of DNA.
- The mutation doesn't alter the amino acid sequence of the protein.
- The mutation causes a change in the amino acid sequence that has no effect on the function of the protein.
84
What is a loss-of-function chromosomal mutation?
Results in a change in amino acid sequence that impairs normal protein function. Frequently shows recessive inheritance.
85
What is a gain-of-function chromosomal mutation?
Results in a change in amino acid sequence that leads to an abnormally functioning protein. Frequently shows dominant inheritance.
86
What is asexual reproduction?
Offspring are derived from a single parent based on mitosis. Offspring are clones of the parent (binary fission in archaea and bacteria).
87
What is bacterial conjugation?
Where bacteria exchange parts of their bacterial chromosomes or plasmids.
88
What is sexual reproduction?
Where offspring are produced from the union of gametes from 2 genetically different parents. Involves the alternating process of meiosis and fertilisation.
89
What are the costs of sexual reproduction?
- The need to maintain the molecular machinery for sexual reproduction.
- The need to find a mating partner.
- Decreased reproductive capacity.
90
What are the benefits of sexual reproduction?
- High genetic variability helps a species adapt to environmental change.
- Brings together advantageous alleles.
- Paired chromosomes allow deleterious mutations to be masker.
91
What are the steps of meiosis 1?
Early prophase - Chromatin begins to condense.
Mid prophase - Synapsis aligns homologs.
Late prophase - Chromosomes continue to coil and shorten, and crossing over occurs (exchange of material between paired chromatids).
Metaphase - Homologous pairs line up on metaphase plate.
Anaphase - The homologous chromosomes (each with 2 chromatids) move to opposite poles of the cell.
Telophase - The original cell divides.
92
What are the steps of meiosis 2?
Prophase - The chromosomes condense again.
Metaphase - The paired chromatids line up across the equatorial plates of each cell.
Anaphase - The chromatids separate and are pulled to opposite poles of the cells, becoming chromosomes.
Telophase - The cells divide creating 4 cells with different genetic makeups due to crossing over and independent assortment.
93
What is independent assortment?
The homologous chromosomes line up at the metaphase plate and segregate independently of each other.
94
What are linked genes?
Genes that are located on the same chromosome. They do not follow the law of independent assortment.
95
What is crossing over during meiosis?
The exchange of parts of DNA between chromosomes. Leads to recombinant chromatids that contain a mix of DNA from both homologues. Further increases genetic variation.
96
What does hemizygous mean?
Containing only one allele of a gene.
97
What is aneuploidy?
An abnormal number of chromosomes in an organism. Can arise due to non-disjunction - a failure to separate homologous chromosomes during meiosis.
98
What is symbiosis?
The proposed mechanism through which multicellular life initiated. It is proposed that the mitochondria and chloroplasts arose from a symbiosis between 2 cells. They used to be their own cell and retain some of their specialised functions which now benefit their host cells.
99
What do the 37 genes remaining in the mitochondrial genome do in human cells?
13 provide instructions for making enzymes involved in oxidative phosphorylation and the others provide instructions for making tRNA and rRNA.
100
Why is mutation rate for organelle genes higher than for nuclear genes?
Lack of proof-reading and repair mechanisms. Organelle genes are maternally inherited.
