D2.1 Cell and nuclear division Flashcards
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Compare and contrast cytokinesis in animal and plant cells
Animal cells:
- a ring of contractile actin and myosin PINCH cell membrane to split
- forms a cleavage furrow
Plant cells:
- vesicles assemble sections of membrane and cell wall, forming a cell plate
examples of unequal cytokinesis
Oogenesis: the formation of eggs in females. Involves unequal division of cells during meiosis to produce one large egg cell.
Budding: A form of asexual reproduction in yeast where a smaller daughter cell buds off from its parent cell by cytokinesis.
prophase I
- homologous chromosomes pair up to form bivalents
- crossing over occurs (alleles switch between non-sister chromatids)
- nuclear envelope breaks down
- spindle fibres start to form
- centrioles move towards the poles
metaphase I
- spindle fibres move the bivalents (homologous chromosomes) to the equator of the cell
- sister chromatids are attached to spindle fibres by the centromere
- maternal and paternal homologous chromosomes are randomly assorted as they are lined up along the equator
anaphase I
- homologous chromosomes of the bivalents are separated and are pulled towards the poles by microtubule motors on the kinetochore
telophase I
- sister chromatids arrive at the poles and uncoil
- nuclear membrane forms around sister chromatids at each pole, producing 2 haploid nuclei
- cytokinesis occurs, producing 2 haploid cells.
prophase II
- chromosomes, as sister chromatids, supercoil and appear in both haploid cells
- centrioles move towards the poles, producing spindle fibre microtubules
- sister chromatids attach to spindle fibres at centromere
metaphase II
- sister chromatids line up at the equator
anaphase II
- sister chromatids pulled apart, producing single stranded chromosomes
- single stranded chromosomes moved towards the poles by microtubule motors on the kinetochore
telophase II
- chromosomes reach the poles of the cell and uncoil
- nuclear membrane forms around each set of chromsomes
- cytokinesis occurs in both cells, forming 4 cells with haploid nuclei which are not identical
Down syndrome
Extra chromosome results from non-disjunction, where the 21st chromosome pair does not separate during anaphase I
If non-disjunction happens in the ovary, the egg carries 2 chromosome 21’s instead of one. When fertilised by sperm, resulting in 3 chromosome 21’s.
Why the need for genetic diversity? (crossing over and random orientation)
increase variety among offspring - increases the chances of survivability if one combination of alleles proves to be more favourable to survive than the others
Describe crossing over
The exchange of genetic material between non-sister chromatids by breaking, twisting around the same point, and connecting to the other’s initial point.
occurs during prophase I
allows for DNA transfer between maternal and paternal chromosomes, forming recombinant chromatids
Describe random orientation
occurs during metaphase 1 when the homologous pairs of chromosomes line up along the equator of the cell.
Which of the pairs end up at which poles is entirely up to chance = random oreintation`
Proliferation of meristematic cells for plant growth examples
Meristematic cells have the ability to divide rapidly, facilitating plant growth
Apical meristematic tissue found in root tips and branches to help the plant lengthen
Lateral meristematic tissue found in stem tissue to widen stems.
Cell proliferation, animal cells examples
Zygote - An undifferentiated cell that divides by mitosis to make thousands of cells. These cells organise into layers and a hollow sphere to form an embryo. The cells then. begin to differentiate to form other parts of the body.
Skin replacement, wound healing - The skin sheds dead cells, and the bottom layer produces new cells via mitosis.
If skin is broken or wounded, all damaged/lost cells are replaced by mitosis.
Describe the 3 phases of interphase
G1 - the cell grows, accumulating materials such as proteins and nucleotides.
S - DNA replication to produce chromosomes with sister chromatids
G2 - Cell prepares for mitosis by growing and replicating organelles.
DNA condenses from chromatin to chromosomes, microtubules can begin to form
How do cyclins control the cell cycle?
The concentration of cyclins increase and decrease throughout the cell cycle.
Each cyclin must reach a certain concentration/threshold level to pass each checkpoint in the cell cycle
Proto-oncogene (mutation, role, consequences)
Proto-oncogenes play a role in regulating cell division. It mutates to become an oncogene.
Oncogenes modify cell apoptosis such that instead of dying and breaking down, the cell continues dividing by mitosis.
Oncogenes may be mutated due to an outside agent, or a mutagen, e.g. cigarette smoke
Tumour Suppressing Genes (mutation, role, consequences)
Tumour Suppressing Genes regulate the cell cycle by controlling cell growth, apoptosis, and DNA repair.
Mutations in TSG lead to uncontrolled cell division or tumour formation
4 types of tumours
Primary - The one that occurs at the original site of the cancer
Secondary - A metastasis, a cancerous tumour that has spread from the original location to another site of the organism
Benign - Cells forming a mass but not spreading to the other organs
Malignant - Cells that rupture the organ they are in and spread to the rest of the body
what is metastasis
The spread of cancer cells away from their original organ.
e.g. if breast cancer spread to the lungs, the cancer cells are still breast cancer cells not lung cells.
describe prophase
- chromatin fibres condense to form chromosomes
- nuclear envelope disintegrates and nucleoli appear
- mitotic spindle forms as centrosomes builds new microtubules
- kinetochores attach to spindle
- centromeres move to opposite poles of the cell
Describe metaphase
- chromosomes move to the equator of the cell and align
- centromeres now at opposite poles
describe anaphase
- chromatids move towards opposite poles of the cell
- ## they move as a result of motor proteins pushing microtubules in opposite directions
describe telophase
- nuclear envelope reforms around each set of chromosomes
- chromsomes elongate
- nucleoli disappear.
- spindle fibres disintegrate
- cell elongates and is ready for cytokinesis
Difference and role of mitosis and meiosis
Mitosis maintains the chromosome number and genome of cells, for all cells
Meiosis halves chromosome number and encourages genetic diversity, for gametes
Describe the purpose and process of condensation of DNA
To prepare for DNA replication, and avoid tangling and misplacing DNA.
DNA is wrapped around histone proteins, being organised into coils, forming a structure called chromatin. Once supercoiling is complete, the chromosome takes its familiar shape.
What are motor proteins and how do they work?
Motor proteins use microtubules as tracks to push and pull objects around the cell. They can also attach to 2 different microfibres and cause them to slide past each other.
Motor proteins use ATP to produce a conformational change that moves the microtubules.
