Cell Division Flashcards
Cell cycle
G1
S
G2
Mitosis
Cytokinesis
{G1, S, G2 are interphase}
Gap 1
- protein synthesis and replication of organelles
S phase
- DNA synthesis — DNA is replicated
- 2 sister chromatids are held together by centromere
Gap 2
- copied DNA is checked by proof reading enzymes
- if genes aren’t copied correctly, mutations will occur — new cells won’t work
- organelle replication
What is chromatin made up of
DNA + histones
Mitosis
The process or nuclear division where 2 genetically identical nucleus are formed from one parent cell nucleus
Why is mitosis important
- asexual reproduction
- single celled organisms divide to produce 2 daughter cells that are separate organisms
- some multicellular organisms produce offspring from parts of the parent
Do bacteria carry out mitosis?
NO
- they have no linear chromosomes, spindles or centrioles
Prophase
- chromosomes supercoil to shorten and thicken in prophase (condense)
- the nuclear envelope breaks down
- centriole divides in 2 and each daughter centriole goes to pole of cell
- spindle fibres begin to form
Metaphase
- chromosomes line up along equator of the cell
- spindle fibres attach to the centromeres of the chromosome
Anaphase
- the centromere breaks - this separates the sister chromatids
- spindle fibres shorten and pull the chromosomes apart the the poles of the cell
- Each chromatid is identical to the original chromosome in the parent cell it was copied from
Telophase
- new nuclear envelope forms around 2 sets of chromosomes
- spindle fibres break down
- supercoiled chromosomes uncoil into chromatin
Cytokinesis
Mitosis is finished
- cytokinesis occurs and the cytoplasm cleaves to finally produce 2 new genetically identical daughter cells (both identical to parent cell)
- this means daughter cell can do same things the parent cell could do
Differences between animal and plant cell cycles
Animal cells
- most cells will undergo mitosis and cytokinesis
- cytokinesis starts from outside and goes in
Plant cell
- only special cells called meristem cells can divide
- plant cells do not have centrioles
- cytokinesis starts with the formation of a cell plate where the equator was- the new plasma membrane and new cell wall material is then laid down along the cell plate
Cytokinesis in animals, plants & fungi
animals- nip in along ‘cleavage furrow’
plants- along cell plate
yeast (fungi)- budding. Cell undergoes mitosis, then the cell bulges in one side, the new nucleus moves into bulge and the bulge pinched off into a new cell
Meiosis
- 4 daughter cells (haploid)
- genetically different
- start from diploid cells (ovaries & testes)
- gametes
- 2 divisions
Homologous chromosomes
Although they have the same gene, they may contain different alleles from the genes
- because one chromosome is from mum and one from dad
Prophase 1
- chromatin condenses and each chromosome supercoils
- nuclear envelope breaks down and spindle fibres form
- chromosomes arranged in homologous pairs (each have 2 chromatids)
- crossing over occurs where non sister chromatids wrap around each other and may swap sections so that alleles are shuffled
Metaphase 1
- pair of homologous chromosomes still in cross over state attach along the equator of the spindles
- each attach to the spindle by centromere
- pairs are randomly arranged- independent assortment
- the way they line up here determines how they will separate independently in anaphase
Anaphase 1
- chromosomes pulled apart by spindle fibres
- centromeres do not divide, each chromosome consists of 2 chromatids
- crossed over areas separate from each other, resulting in swapped areas of chromosomes and allele shuffling
Telophase 1
- 2 new nuclear envelopes form around each set of chromosomes, cell divides by cytokinesis
- short interphase where chromosomes uncoil
- each new nucleus contains half the original no. of chromosomes, but each chromosome consists of 2 chromatids
in most plant cells, the cell goes straight from anaphase 1 to prophase 2
Prophase 2
- nuclear envelope breaks down
- chromosomes coil and condense
- chromatids no longer identical due to crossing over in prophase 1
- spindle fibres form
Metaphase 2
- chromosomes attach by their centromere to the equator of the spindle
- chromatids randomly arranged
Anaphase 2
- centromeres divide
- chromatids are pulled apart by spindle fibres towards poles
- chromatids randomly separated
Telophase 2
- nuclear envelopes form around each if the 4 haploid cells
- in plants, a tetras of 4 haploid cells is formed
How meiosis produces genetic variation
• Crossing over during prophase 1 shuffles alleles
• Independent assortment of chromosomes in anaphase 1 leads to random distribution of chromosomes
• Independent assortment of chromatids in anaphase 2 leads to further random distribution of genetic material
• Haploid gametes are produced which can undergo random fusion with gametes from another organism of the same species
Specialised cell
A cell that has become differentiated to carry out a particular function
E.g. RBC, root hair cell
Unspecialised cell
Stem cells. Can develop into different types of cells
- embryonic stem cells- can develop into any type of cell
- adult stem cell- can replenish cells when needed
Hierarchy of stem cells
- Totipotent
- Pluripotent
- Multipotent
When stem cells have differentiated into the type of cell they will remain as, they are known as: _____
Terminally differentiated
Erythrocytes
Function: carry O2 round the body (from lungs)
Specialisation: biconcave shape so there is a larger SA to carry oxygen
No nucleus to increase space for O2
Flexible to fit through capillaries
Neutrophils
Function: destroy pathogens in the body
Specialisation: metabolic adaptations to enable them to function at low oxygen
Lobed nucleus
Granular cytoplasm contains many lysosomes containing enzymes to attack pathogens
Squamous epithelial cells
Function: lines areas where diffusion takes place (alveoli and capillaries)
Specialisation: form smooth thin layer of cells in the tissue
Ideal for reducing friction
Adapted to be good at diffusion as short diffusion path
Ciliated epithelial cells
Function: provides the propelling force for transport of substances
Specialisation: hair like structures (cilia), cilia are long and thin hairs to help increase surface area to project into the airways
Sperm cell
Function: fertilise egg
Specialisation: flagella for movement, acrosome contains digestive enzymes to break through hard outer layer, mitochondria, haploid nucleus
Palisade cell
Function: site of photosynthesis
Specialisation: lots of chloroplast, long and thin to increase SA, thin cell walls for diffusion of gases
Root hair cell
Function: absorb water from soil by osmosis
Specialisation: large surface area and covered in hair like projections, no chloroplast, large vacuole
Guard cell
Function: regulate opening and closing of stomata
Specialisation: strong and elastic, large vacuoles
Roles of mitosis
- asexual reproduction
- growth & repair
What is the xylem tissue made up of
- Xylem vessels
- parenchyma cells and fibres
How is the xylem formed
Meristem cells produce small cells which elongate and become lignified which kills the cell contents. The ends break down and become long tubes
Lignin
- Allows adhesion
- stops collapse and helps support
- waterproof
- lack of end walls (continuous) = allows continuous column of water
What is phloem tissue made of
- sieve tubes
- companion cells
How is the phloem formed
Meristem tissue produces cells that elongate and line in end to end to form a long tube. The ends do not break down completely but form sieve plates between cells. They allow the movement of sugars (sucrose) up and down the tubes
Animal tissue is grouped into 4 categories:
- Connective tissue- hold structures together and provide support
- Muscle tissue- contract to bring about movement
- Nervous tissue- convert stimuli and carry electrical impulses
- Epithelial tissue- layers and lining (squamous epithelial and ciliated epithelial)
Squamous epithelial tissue
- made of flattened cells held in place by a basement membrane (collagen + glycoproteins) which attaches the epithelial cells to connective tissue
- they are smooth and very thin and flat. This makes them perfect for lining tubes
- also found in alveoli walls- short diffusion pathway
Ciliated epithelial cells
Found in the lumen of: airways- trachea, bronchi and bronchioles, and fallopian tubes and uterus
• goblet cells secrete mucus which catches particles and microbes - the cilia waft it up to the throat to be swallowed
• Cilia waft egg cells from the ovary along the Fallopian tube
• Cilia move in a synchronised rhythmic wave
