cell division Flashcards
chap 6
What is G0? Why might a cell enter G0?
The resting phase, in which the cell leaves the cycle temporarily or permanently
When a cell is specialized it no longer needs to divide, hence entering G0
Which cells DON’T divide?
DNA damaged cells and senescent cells
What happens at each checkpoint of the cell cycle? (4, 3, 2)
G1 checkpoint checks for:
cell size, nutrients, growth factors, DNA damage
G2 checkpoint checks for:
cell size, DNA replication, DNA error
Spindle assembly checkpoint checks for:
all chromosomes attached to spindles and being aligned
What happens at G1 phase? (3)
- proteins synthesised
- organelles replicated
- cell enlarges
What happens at synthesis phase?
DNA replicated
What happens at G2 phase? (3)
- energy stores are increased
- DNA checked for errors
- cell enlarges
True or false- chromatids are singular structures of DNA and chromosomes are the X ones
False- chromatids and chromosomes are the same thing! X pairs are typically called sister chromatids and when they split into singular structures they are then chromosomes
What is the role of the centromere in mitosis? (3)
- holds chromatids together
- attaches chromatids to spindle fibres
- allows chromatids to be separated
MITOSIS: Prophase (3)
- chromatins condense to form chromosomes/chromatids
- nuclear envelope breaks down
- spindle fibres form at poles
MITOSIS: Metaphase
chromosomes lined up at metaphase plate (equator)
MITOSIS: Anaphase (2)
- centromeres divide
- spindle fibres contract to separate sister chromatids
MITOSIS: Telophase (3)
-chromatids/chromosomes reach poles and coil
- nuclear envelope reforms
- nucleolus formed
MEIOSIS I: Prophase I
Chromosomes pair up into BIVALENTS + CROSS OVER
MEIOSIS I: Metaphase I
Homologous pairs (4 chromatids) line up via INDEPENDENT ASSORTMENT
MEIOSIS I: Anaphase I
Chromosomes are pulled to poles + chromatids become RECOMBINANT (as DNA breaks off and rejoins at CHIASMATA)
How is MEIOSIS II different to mitosis? (2)
- results in 4 genetically different, haploid cells
- recombinant chromatids don’t need to pair up and can line up as is
Functions of 4 types of tissues
- Connective: holds tissues together + transport medium
- Muscular: contracts
- Nerve: transmits electrical impulses
- Epithelial: covers internal and external body surfaces
True or false- all cells have a different part of the human genome
False- all cells share an identical genome but it is the activation of genes that cause differentiation
3 adaptations of erythrocytes
- flattened biconcave shape
- no nuclei
- flexible (to squeeze thru capillaries)
4 adaptations of sperm
- acrosome (contains lysozymes)
- flagellum
- many mitochondria
- streamlined
2 adaptations of neutrophil
- multi-lobed nucleus (move around quicker, change shape, extend cytoplasm to engulf)
- granular cytoplasm (contains many lysosomes)
4 adaptations of palisade
- many chloroplasts
- rectangular
- thin walls
- large vacuole
2 adaptations of root hair
- long extensions
- concentrated vacuole sap
2 adaptations of guard cell
- thicker inner wall (on one side, so stoma can actually shut properly as shape isn’t symmetrical)
- ring of cellulose
2 adaptations of squamous epithelium
- flattened cells
- permeable (for selective diffusion)
2 adaptations of ciliated epithelium
- cilia
- goblet cells
Stem cells (what are they able to do?)
undifferentiated cells w the potential to differentiate into any one of the range of specialised cell types of an organism (can renew themselves constantly)
3 tiers of stem cell potency and explain what this means (and give examples)
Totipotent eg zygotes
- differentiate into all tissue types, AND extra-embryonic tissues, SO whole organism
Pluripotent eg embryonic stem cells
- differentiate into all tissue types (not extra-embryonic or whole organism)
Multipotent eg adult stem cells
- differentiates into a limited range of cell types
2 types of plant stem cells? where are they in the plant? how does the one of them help the other?
Meristematic tissue
- wherever growth occurs (eg roots and shoots)
Vascular cambium
- between xylem and phloem
- stay pluripotent throughout life cycle so provide secondary growth for meristems
2 uses of stem cells (and 2 sub-uses for each)
Medicine (for treatment of damaged tissues and neurological diseases)
Research (developmental biology and drug trials)
2 advantages and 1 disadvantage of embryonic stem cells
- makes use of discarded embryos from IVF
- plentiful, easy to harvest
- EMBRYO RIGHTS
1 advantage and 1 disadvantage of umbilical stem cells
- avoids ethical issues
- only multipotent (so limited)
What are induced pluripotent stem cells (iPSCs) and give 1 advantage?
Adult stem cells that have been genetically modified to be pluripotent
- less chance of rejection
2 adaptations of epidermis tissue
- single layer of many, closely packed chloroplasts
- waxy and waterproof
How does differentiation occur?
Stem cells can use all their genes, and switch certain ones on or off to specialise
Why is it important for neutrophils and erythrocytes to be constantly produced? Why for erythrocytes?
- both have very short lifespans
- erythrocytes have no nucleus + organelles so can’t undergo mitosis
How are erythrocytes and neutrophils produced?
colonies of hematopoietic stem cells in the bone marrow specialize them
How are xylem vessels produced from meristems? (3)
- lignin deposited in cell walls (so waterproof)
- cells die
- end walls break down, forming a continuous, wide tube to carry H20
How are phloem sieve tubes produced from meristems? (4)
- sieve tube elements lose their nuclei
- end walls develop sieve plates
- companion cells retain organelles
- carry out metabolism to obtain ATP to load sugars into sieve tubes
How does cytokinesis produce 2 daughter ANIMAL cells? (3)
- cleavage furrow forms around the middle
- plasma membrane is pinched inwards by cytoskeleton
- fuses in the middle
How does cytokinesis produce 2 daughter PLANT cells? (3)
- cell walls = no cleavage furrow
- SO vesicles assemble at equator and fuse with each other + plasma membrane
- new cell wall forms from new membrane
