topic 7 Flashcards
what are the 2 main steps in the cell cycle
- Interphase
o Growth phase
o Increase in mass, synthesising cell contents
o Cell stays here majority of the time
o Made up og G1, S and G2 - Miotic phase (or M phase)
o Cell division via mitosis and cytokenesis
Describe each step of the cell cycle
Interphase G1
- G= gap
- Synthesis of RNA, proteins and organelles
- But not chromosomes c
- Cell grows in mass
- Depending on type of cells, duration varies
- Typically about 8-10 hrs
- Fast growing cells: few mins to hrs
- Decide if cell should proceed to cellular division
- Stays in G2 to G0
Interphase: S phase
- S= synthesis
- Replication of DNA
- In prep for cell division
- Relatively short phase
- Approx 5 hrs
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Interphase:G2
- Cell @ double checks” for error
- DNA repair
- Prepares for mmitosis (cell growth and protein synthesis )
- Typically 4-6 hours
Mitoic phase (M)
- M phase : mitosis and cytokinesis
- Cell undergoes nuclear division
- Results in two genetically identical cells
- Typically 30-45 mins
describe the importance of cell cycle regulation
Cell cycle regulation
- Quality control checkpoints : ensures cell is ready for cell division and is error free
Ensures appropriate sequence and timing of cell cycle phases
Ensures phase completion before transition to the next phase
Able to response to external conditions – eg growth factors and nutrients
- If conditions are not met, cell will not progress further
- if conditions are met, cell will progress by regulatinf the activities of cyclins and cyclin-dependent kinases (Cdks)
cell cycle regulation
3 main checkpoints
- G1- S transition control
- G2- M transition control
- Metaphase- anaphase transition control
G1-S transition control
- Occurs towards the end of G1
- Checks whether cell is ready for S phase (DNA replication)
Cell is big enough
Have the necessary proteins
Whether DNA is damaged
- If not cell goes through a resting period (G0) until ready to divide
G0
- Cell exists from cell ccle
- If cell is not proceeding to S phase
- G0: cells are dormant (quiescence) – not preparing to divide
- Non- dividng cells undergo terminal differentiation
- Ege nerve cells
- Ccan be triggered to re-enter G2 if there is a signal eg heptocyctes
G2-M transition control
* Occurs at the end of G2 (Boundary of G2 – M)
* Checks whether cell is ready for M phase (cellular division)
* Cell is big enough
* DNA replication is complete
* Have the necessary proteins
* Under certain conditions (if above conditions are not met), an arrest stage can occur if division isn’t necessary
Metaphase-anaphase control
* Occurs in the mitotic phase (specifically in between metaphase and anaphase)
* Checks whether mitosis process is goingwell:
* Whether the two chromatids (of the chromosome) are properly attached to the spindle fibres
* Ensures that daughter cells receive complete set of chromosome
LLO7.3 Describe apoptosis and compare and contrast apoptosis to necrosis
- Apoptosis
Programmed cell death
Part of normal healthy process
Maintains genomic integrity
Regulated by aptotic signals and effectos
Triggered by apotic signalling and dna damage
Normal growth and developmental processes - Necrosis
Premature uncontrolled death where cells swells and ruptures, releasinf cellular contents
Result of external factos (disease, injury, hypoxia)
Effects many cells
Always destructive
4 Describe briefly how DNA is packaged in the nucleus
na are packaged into nucleosomes (with histones) -> chromatin fibre -> loops-> heterochromatin -> chromosome
- Widget of a chromosom 1400nm
Describe and explain the process of the mitotic division and the features of the cells produced by the process
- Defined when condensied chromosomes are visible by light microscopy
- Sister chromatids still attached to eachother
- Centrosomes migrate away from each other
- Centrosomes migrate away from each other
- Formation of mitotic spindle
- Network of microtubules metween centrosomes
- Formation of aster near each centrosome
Dense starburst of mictotubules
Mitosis: prometaphase
- Defined by the fragmentation of nuclear membranes
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- Breakdown of nuclear envelope
- Centrosomes moving toward opposite sides
- Spindle microtubules attach to chromatids at centromere (via kinetochore)
Mitosis: metaphase
- Defined by the alignment of fully condensed chromosomes along the metaphase plate
- Equal distance between the two poles
- Metaphase-anaphase transition point
Checkpoint before ana phase
Mitosis: anaphase - Usually shortest phase
- Chracterised by two kinds oof movement
o Anaphase A: chromosomes pull toward spindle poles via centromete
o Anaphase B: spindle poles move away from each other
o May occur sequentially or simultaneously
Mitsosis: telophase - Daughter chromosomes reach spindle poles
- Nuclear envelope forms around daughter chromosomes
- Chromosome uncoils, to reume interphase chromatin structure
- Spindle disassemble
- Phase simultanceously occurs with cytokinesis
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Cytokinesis
- Second process is mitotic cell division
- Separated cytoplasm
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- Cleabage furrow formed by actin along the spindle equator
Infer the consequences of errors in mitosis
- One parent cell divises into two genetically identical daughter cells
- Outcomes:
Mutations can be carried through subsequent generation
May lead to cencer
No genetc diversity
Describe and explain the process of meiosis and the features of the cells produced by the process
Meiosis 1
Reduction division
Prophase 1:
- Homologous chromosome pair upp
Process of syapsis forms bivalents
Mediated by cynaptonemal complex
Crossing over occurs
Chiasma visible and synaptoemal complex disaooears
Nuclear envelope freagments
Meisosis 1: metaphase 1
- Bivalent (paired homologous chromosome) migrate and align at spindle equator
Meisosis 1: anaphase 1
- Sister chromatids (chromosomes) move together towards spindle pole
Telophase 1 and cytokinesis
Telophase 1: when chromosomes reaches the spindle pole
- Formation of nuclear envelope
Cytokinesis
- Generates two haploid cells
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- Ceahc cell contains chromosomes that has two sister chromatids
Meiosis 2
- Equtional division
- Similar to mitotic division
- Sister chromatids separate
- No DNA replication (only hald as many chromosomes present)
- Consists of prophase 2, metaphase 2, anaphase2, telopjse 2 and cytokinesis
- Results in 4 haploid cells at the end
LLO7.8 Explain how new combination of genes are produced in every generation
Exchange of genetic information
- Two ways
1. Crossing over
- Requires chromosome to be of close proximity
- Physical exchange of genetic information (of corresponding regions of homologous chromosome)
2. Independent assortment
- Chromosomes are distributed between the daughter cells independently of each other
Compare and contrast the process of mitosis and meiosis
Mitosis
- Occurs in somatic cells
- Purpose is for cellular proliferation
- Produces 2 diploid daughter cells (46 chromosomes, 92 chromatids )
- Chromosome number remains the same
- Genetic variation doesn’t change
Meiosis
- Happens in sex cells
- Purpose is for sexual reproduction
- Produces 4 haploid daughter cells (23 chromsomes 25 chromatids)
- Chromosome number is halved in each daughter cell
- Genetic variation increased
Infer the consequences of errors of meiosis
defects in meiosis
- Arises due to chromosmes abnormalities
- Abnormalities in chromosome umber
- Abnormaliesits in chromosome structure
Nondisjunction
- Chromosome partitioning erroe
- Either in meiosis 1 or 2
- Results in abnormal number of chromosome (aneuploidy)
- Eg down syn
In chromosome structure
- Deletions
- Duplications
- Translocations
- Inversion
- Associated with cancer
Describe the concepts and principles underlying Mendelian genetics, including Mendel’s Law of Segregation, dominance and independent assortment
Mendelian genetics
- Traits that are passed down from parents
- Named after Gregory mendel
- Performed cross-polination experiments on garden peas to study inheritance
Law of dominance
- In cross-fertilisation, dominant trait will always mask the recessive trait
Law of segregation
- The two alleles of a gene are separate entities and separate from eachother during gametoegenesis
Law of independent assortment
- Chromosomes are distributed to gammetes independently
- Alleles for different traits are distributed independently if they are on different chromosomes
- All combnation of traits possible
Distinguish between incomplete dominance and co-dominance and describe how it affects individuals using examples (e.g. blood groups) Incomplete dominance
Incomplete dominance
- Neither allele is wholly dominant
- Heterozygous individuls exhibits blessed phenotype
- Eg intermediate colour between the two parental omozygous traits
- eg red and white flower = pink
Codominace
- Non-identical allelces axpressed equally in heterozygous individual- traits are discrete
Neither allele is dominant over the other
- brown and white cow make a spotty brown and wite offspring
- Phenotype of the heterozygous individual include phenotupe of both elleles
Blood groups
- ABO blood group in an individual is determined by the carbohydrates that is expressed on the RBC
- Alleles in the human express carbohydrate antigen on surface of RBC
Alleles IA I B or I ( does not express any carbohydrate)
Blood groups
- Two possible antigens A and B
- Humans can have and express:
- 0 of the 2 alleles (O blood)
- 1 of the 2 alleles (either A or B)
- 2 of the alleles (AB blood)
- Codomiance is seen in AB blood groups
describe the factors that determine sex in humans
Y chromosome
- Smaller the x chromosome (contains less DNA)
- Both ends of y chromosome are homologous to X chromosome
- Dervived from male parent
- Contains sex-determinfing region y (SRY) gene
- Expressed 6-8 weeks into gestation (zygotes are phenotypically identical prior )
- Initiates sexual differentiation- development of testes rather than ovaries
Analyse, compare and contrast the types of genetic inheritance and its pedigree
Autosomal dominant
- Sexes equally affected (50% chance)
- Transmission by mother or father
- Trait will generally be present (does not skip generations)
- Propbability of child receiving trait > or = 50%
- Since only one allel is required to cause trait
- Eg eye colour, huntings disease
Autosomal recessive
- Sexes equally effected
- Transmission by bother and father
- Trait only present if both alleles are present (can skip generations)
- Probability of child receiving trait 25% (if parents are heterozygous)
- Since two alleles are required to cause trait
- Bothparents have at least one recessive allele each
- Eg cystic fibrosis
- Sex-linked
Sex-linked dominant
- X-linked : allele on x chromosom
- Transmission by mother (to daughter or son) ro father (to daughter only)
- Trait eill generally be present (does not skip generations )
- Since only one allele on an X chromosome is required to cause trait
- Caughter with 1 copy of allele may have less sever phenotype due to having 2X chromosomes
- Eg. Rett syndrome
Sexlinked recessive
- X-linked allele on X chromosome
- Transmission by mother (to daughter or son ) or father ( to daughter only
- Trait only present of both alleles are present for daughter or allele is presenr for son (can skip generations)
- ( for daughters) since two alleles are required to cause trait
- Both parent have at least on affected allele on the X chromosome each
- Daughter are most likely to be carriers, less likely affected
- Sons are affected (since there is only one X chromosome)
