C6 - Cell division Flashcards
What are the phases of the cell cycle?
Interphase
Mitotic phase
What is interphase
Growth period of the cell consisting of stages G1, S and G2, between cell division
What happens during interphase?
-DNA replicated and checked for errors in the nucleus
-Protein synthesis occurs in the cytoplasm
-Mitochondria (and chloroplasts) grow and divide
-Normal metabolic processes of cells also occur
What is the G1 stage?
First growth stage - proteins which synthesise organelles are produced and organelles replicate, the cell increases in size
What is the S phase?
Synthesis phase - DNA is replicated in the nucleus
What is the G2 phase
Second growth phase - cell continues to increase in size, energy stores are increased and duplicated DNA is checked for errors
What is the mitotic phase
Period of cell division consisting of mitosis and cytokinesis
What happens during mitosis
Nucleus divides
What happens during cytokinesis
Cytoplasm divides and two new cells are produced
What is G0
Phase when cell leaves the cycle permanently or temporarily?
What are the reasons for a cell entering G0
-Differentiation: cell that becomes specialised to carry out a specific function is no longer able to divide
-DNA of cell may be damaged: no longer viable
-Aging: growing number of senescent cells
What are checkpoints?
Control mechanisms of the cell cycle
Where do checkpoints occur?
G1 checkpoint- end of G1 phase, before entry into S phase
G2 checkpoint- end of G2 phase, before mitotic phase
Spindle assembly (metaphase) checkpoint- when all chromosomes attached to spindles and aligned
What does G1 checkpoint check?
Cell size
Nutrients
Growth factors
DNA damage
What does G2 checkpoint check
Cell size
DNA replication
DNA damage
-If passed, signals beginning of mitosis
What does spindle assembly checkpoint check?
Chromosome attachment to spindle
-Mitosis cannot proceed if checkpoint isn’t passed
What is mitosis?
Nuclear division stage in cell cycle
Creating two genetically identical daughter cells
What is mitosis important for?
Asexual reproduction
Growth
Tissue repair
What has to happen before mitosis can occur? (chromosomes)
Interphase - DNA in nucleus replicated
Each chromosome is converted into two identical DNA molecules called chromatids
Chromatids joined together at region called centromere
What are the four stages of mitosis
Prophases
Metaphase
Anaphase
Telophase
What happens to chromosomes through mitosis
What happens during prophase?
1) Chromatin fibres coil and condense to form chromosomes
2) Nucleolus disappears
3) Nuclear membrane begins to break down
4) Protein microtubules form spindle-shaped structures linking poles of cell
-Animal and some plants: centrioles migrate to poles and form spindles
5) Spindle fibres attach to specific areas on centromeres and move chromosome to centre of cell
5) By end, nuclear envelope disappeared
What happens during metaphase?
1) Chromosomes moved by spindle fibres to form a plane in the centre of the cell (metaphase plate)
2) Held in position
What happens during anaphase?
1) Centromeres holding together pairs of chromatids in each chromosome divide
2) Chromatids separated and pulled to opposite poles by shortening spindle fibres
What happens during telophase?
1) Chromatids have reached poles and are called chromosomes
2) Two new sets of chromosomes assemble at each pole
3) Nuclear envelope reforms around them
Light micrograph of mitosis of root tip cells
What is cytokinesis
Cell division stage in the mitotic phase of the cell cycle that results in the production of two identical daughter cells
How does cytokinesis occur in animal cells?
Cleavage furrow forms in middle of cell
Cell surface membrane pulled inwards by cytoskeleton until its close enough to fuse
How does cytokinesis occur in plants?
No cell wall
Vesicles from Golgi apparatus begin to assemble
Vesicles fuse with each other and cell surface membrane, dividing cell membrane into two
What is meiosis?
Form of cell division where the nucleus divides twice resulting in halving of the chromosome number and producing four haploid cells from one diploid cell
What are gametes?
Haploid sec cells produced in meiosis in organisms that reproduce asexually
What is a zygote?
Initial diploid cell formed when two gametes are joined by sexual reproduction (earliest stage of embryonic development)
What is reduction division?
Cell division resulting in the production of haploid cells from a diploid cell
What is a haploid?
Half the normal chromosome number, one chromosome of each type
What are homologous chromosomes?
Matching pair of chromosomes, one inherited from each parent
What are the two stages of meiosis called
Meiosis I
Meiosis II
What happens in prophase 1
Chromosomes condense
Nuclear envelope disintegrates
Nucleolus disappears
Spindle formation begins
-Homologous chromosomes pair up forming bivalents
-Moving chromosomes through cytoplasm causes chromotids entangling, crossing over
What is metaphase 1?
Homologous pairs of chromosomes moved by spindle fibres to form a plane in the centre of the cell (metaphase plate)
Orientation of homologous pairs is random and independent
Independent assortment results in genetic variation
What is anaphase 1?
Homologous chromosomes are pulled to opposite poles
Sections of DNA on sister chromatids became entangled during crossing over
They break off and rejoin, sometime resulting in exchange of DNA (chiasmata -points where they break off)
When exchange occurs, recombinant chromatids formed with genes exchanged
Genetic variation arises from this new combination of alleles and sister chromatids not identical
What is telophase 1?
Chromosomes assemble at each pole
Nuclear membrane reforms
Chromosomes uncoil
What is prophase 2?
Chromosomes, consisting of two chromatids, condense
Nuclear envelope breaks down
Spindle formation begins
What is metaphase 2?
Individual chromosomes assemble on metaphase plate
Chromosomes no longer identical so there is independent assortment causing more genetic variation
What is anaphase 2?
Chromatids of chromosomes pulled to opposite poles, after division of centromeres
What is telophase 2?
Chromatids assemble at poles
Chromosomes uncoil and form chromatin
Nuclear envelope reforms
Nucleolus reappears
How are erythrocytes specialised?
ROLE: transporting oxygen around body (rbc)
-Flattened biconcave shape: increases SA:V ratio, increasing rate of diffusion
-No nuclei and lacking some organelles: increasing space available for haemoglobin (carries O2)
-Flexible: enables them to squeeze through narrow capillaries
How are neutrophils specialised?
ROLE: immune system (wbc)
-Multi-lobed nucleus: easier to squeeze through small gaps to reach site of infection
-Granular cytoplasm contains lysosomes: contain enzymes to attack pathogens
How are sperm cells specialised?
ROLE: deliver genetic material to female gamete (male gametes)
-Tail/flagellum: capable of movement
-Contain many mitochondria: supply energy needed to swim
-Acrosome on head contains digestive enzymes: released to digest protective layer surrounding ovum, enabling sperm to penetrate and fertilise
How are palisade cells specialised?
ROLE: present in mesophyll
-Contain chloroplasts: absorb large amounts of light for photosynthesis
-Rectangular box shaped cells: can be closely packed together
-Thin cell walls: increasing rate of diffusion of CO2
-Large vacuole: maintains turgor pressure
-Chloroplasts move within cytoplasm: to absorb more light
How are root hair cells specialised?
ROLE: present near growing tips
-Long extension called root hairs: increase SA of cell maximising uptake of waters and minerals from soil
How are guard cells specialised?
ROLE: on surface of leaves
-Form stomata: necessary for CO2 to enter plant
-When guard cells lose water and become less swollen, they change shape, closing to prevent water loss
-Cell wall thicker on one side: cell does not change shape symmetrically as its volume changes
How is squamous epithelium adapted?
ROLE: made up of specialised squamous epithelial cells
-Very thin as its one cell thick: fast diffusion rates
How is ciliated epithelium adapted?
ROLE: made up of ciliated epithelial cells
-Hair-like structure that move in a rhythmic manner
(+goblet cells secreting mucus to sweep away particles in trachea)
How is cartilage adapted?
ROLE: connective tissue
-Contains fibres of proteins: elastin and cartilage
-Cartilage is a firm flexible connective tissue: prevents bones rubbing together
How is muscle adapted?
ROLE: contacting to move bones
-Contains skeletal muscle fibres which contains myofibrils containing contractile proteins
How is the epidermis adapted?
ROLE: single layer of closely packed cells covering surface of plants
-Covered by waxy, waterproof cuticle: reduce water loss
-Stomata are present: allow gas exchange
How is xylem tissue adapted?
ROLE: vascular tissue responsible for transport of water and mineral ions
-Walls strengthened with waterproof lignin: provides support
How is phloem tissue adapted?
ROLE: vascular tissue responsible for transport of organic nutrients from leaves and stems to place they are required
-Composed of sieve tubes separated by sieve plates
