B6 - Cell division Flashcards
(49 cards)
1
Q
What are the phases of the cell cycle?
A
- interphase
- mitotic (division) phase
2
Q
What takes place during interphase?
A
- DNA replication/checked
- protein synthesis
- mitochondria grow/divide
- chloroplasts grow/divide
- metabolic processes occur
3
Q
What are the three stages of interphase?
A
- G1= first growth phase
- proteins are synthesised
- organelles replicate
- mRNA made
- cell increases in size
- S = synthesis phase
- DNA is replicated in nucleus (produces chromatids)
- G2 = second growth phase
- cell continues to increase in size
- energy stores increased
- duplicated DNA is checked for errors
4
Q
What are the three checkpoints of the cell cycle?
A
- G1 checkpoint = end of G1
- cell size
- nutrients
- growth factors
- DNA damage
- if it does not meet the requirements, it enters the G0 phase (resting state)
- G2 checkpoint = end of G2
- cell size
- DNA replication
- DNA damage
- spindle assembly = metaphase checkpoint
- all chromosomes should be attached to spindles/aligned
- mitosis cannot proceed until this checkpoint is passed
5
Q
What is G0?
A
- phase where a cell leaves the cycle (temporarily/permanently)
- differentiation = specialised cells are unable to divide (will not enter cell cycle again)
- damaged DNA = unable to divide and enters period of permanent arrest
- number of (senescent) cells increases as you age, which has been linked to diseases such as cancer/arthritis
- lymphocytes are able to go back into cell cycle in an immune response
6
Q
What is the mitotic phase?
A
- mitosis = the division of the nucleus
- cytokinesis = cytoplasm divides and two cells are produced
7
Q
Why is mitosis important?
A
- growth
- tissue repair
- asexual reproduction in plants, animals, fungi
- replacement of old cells
8
Q
What are the main stages of mitosis?
A
- prophase
- metaphase
- anaphase
- telophase
9
Q
What happens during prophase?
A
- chromatins condense to form chromosomes (not visible during interphase)
- nucleolus disappears and nuclear envelope breaks down
- protein microtubules form spindle fibres, linking the poles of the cell
- centrioles (protein bundle) move to opposite poles
- spindle fibres attach to centromeres and begin to move the chromosomes
10
Q
What happens during metaphase?
A
- the spindle fibres move the chromosomes to the centre of the cell
- forms a metaphase plate and is held in position
11
Q
What happens during anaphase?
A
- the centromeres divide, separating each pair of sister chromatids
- the spindle fibres shorten and pull the chromatids to opposite sides of the cell
12
Q
What happens during telophase?
A
- the chromatids are now called chromosomes
- nuclear envelope reforms around them
- chromosomes uncoil and nucleolus forms
- nuclei are genetically identical to each other
13
Q
What is cytokinesis?
A
- the division of the cytoplasm
14
Q
What happens during cytokinesis in animal cells?
A
- cleavage furrow forms around centre of cell
- cytoskeleton pulls the cell membrane inwards to fuse around the middle
- forms two new cells
15
Q
What happens during cytokinesis in plant cells?
A
- vesicles from Golgi apparatus assemble where the metaphase plate was formed (centre of cell)
- vesicles/cell membrane fuse together and forms two new cells
- new sections of cell wall form along new cell membrane
16
Q
What is meiosis?
A
- the formation of gametes (haploid)
- a gamete contains half the chromosome of parent cell
- fertilised egg = zygote
- reduction division
17
Q
Why is meiosis important?
A
- produces genetically unique daughter cells
- crossing over
- independent assortment
18
Q
What are homologous chromosomes?
A
- matching sets of chromosomes (in nucleus)
- diploid
- each chromosome in the pair has the same genes at the same position
19
Q
What are the stages of meiosis?
A
- meiosis I (first division - reduction)
- meiosis II (similar to mitosis
20
Q
What happens during meiosis I?
A
- prophase I:
- chromosomes condense and nucleolus disappears
- homologous pairs pair up and form bivalents
- when moving through the cytoplasm, crossing over takes place as chromatids tangle
- metaphase I:
- pairs of chromosomes assemble along metaphase plate
- orientation of the pairs are random and independent (independent assortment)
- anaphase I:
- the chromatids are still joined together when pulled to opposite poles
- they then break off and rejoin (forms recombinant chromatids)
- telophase I:
- chromosomes assemble at each pole and nuclear membrane reforms
- cell undergoes cytokinesis and forms two cells
21
Q
What happens during meiosis II?
A
- prophase II:
- chromosomes condense and become visible
- spindle formation begins
- metaphase II:
- individual chromosomes assemble at metaphase plate
- more independent assortment/genetic variation
- anaphase II:
- chromatids of individual chromosomes are pulled to opposite poles
- chromatids of individual chromosomes are pulled to opposite poles
- telophase II:
- chromatids assemble at each pole
- chromosomes uncoil and nuclear envelope reforms
- cytokinesis forms four genetically unique daughter cells
22
Q
What are specialised cells?
A
- cells that are differentiated (adapted to carry out specific functions)
23
Q
How are erythrocytes specialised?
A
- flattened biconcave shape = increases SA:V
- no nuclei = increases space for haemoglobin
- flexible = able to squeeze through capillaries
24
Q
How are neutrophils specialised?
A
- multi-lobed nucleus = can squeeze through small gaps
- granular cytoplasm = contains lysosomes (enzymes to attack pathogens)
25
How are sperm cells specialised?
- flagellum/many mitochondria = movement/swimming
- digestive enzymes in head = digest layers around ovum
26
How are palisade cells specialised?
- chloroplasts (can move around) = photosynthesis
- box shape = can be closely packed together
- thin cell walls = increase rate of CO2 diffusion
- large vacuole = maintains turgor pressure
27
How are root hair cells specialised?
- root hairs = increase SA of cell (maximises uptake of water and minerals)
28
How are guard cells specialised?
- lose water = closes stomata to prevent further water loss
- thicker on one side = cell does not change shape symmetrically
29
What are tissues?
- collection of differentiated cells that have a specialised function
30
What are the main tissues in animals?
- nervous = transmission of electrical impulses
- epithelial = cover body surfaces
- muscle = contract
- connective = hold other tissues/transport medium
31
How is squamous epithelium specialised?
- very thin = rapid diffusion
- (forms lining of lungs)
32
How is ciliated epithelium specialised?
- hair-like features = sweeps away mucus from lungs
- goblet cells = secrete mucus to trap air particles
33
How is cartilage specialised?
- contains fibres of elastin/collagen = firm and flexible
- prevents ends of bones rubbing
34
How is muscle specialised?
- (skeletal) contain myofibrils = allow for contraction
- help to move bones in body
35
What are the main tissues in plants?
- epidermis = cover plant surfaces
- vascular = transport of water/nutrients
36
How is epidermis specialised?
- waxy cuticle = prevents water loss
- stomata = allow CO2/H2O/O2 in and out
37
How is xylem tissue specialised?
- vessel elements = transport water/minerals
- lignified walls = structural support
38
How is phloem tissue specialised?
- columns of sieve tube cells (sieve plates) = transport of organic nutrients
39
What is an organ?
- collection of tissues adapted to perform a particular function
40
What are the organ systems in animals?
- digestive = breaks down large insoluble molecules and absorbs nutrients
- cardiovascular = moves blood around body
- gaseous exchange = brings air into body
41
What are stem cells?
- undifferentiated cells that have the potential to become one of the specialised cell types
- able to undergo cell division multiple times
- (uncontrolled division can cause development of cancer)
42
What are the different stem cell potencies?
- totipotent = can differentiate into *any* type of cell
- pluripotent = can form all *tissue* types but not whole organisms
- multipotent = can only form a range of cells found *within a certain type* of tissue
43
What is differentiation?
- when cells become adapted to their specific role
44
What are the sources of animal stem cells?
- embryonic:
- present at early stages of embryo development (*totipotent*)
- blastocyst = *pluripotent*
- adult:
- present throughout life
- can be found in bone marrow
- *multipotent*
- can also be derived from umbilical cords
45
How are erythrocytes and neutrophils produced?
- formed from bone marrow stem cells
- erythrocytes = lose nucleus, builds up haemoglobin
- neutrophils = indentations of nucleus, granules accumulate
46
How are xylem vessels and phloem sieve tubes produced?
- from cambium
- xylem = lose cytoplasm, deposit lignin, lose end walls
- phloem = lose some cytoplasm/organelles, develop sieve plates
47
What are the sources of plant stem cells?
- meristematic tissue (found wherever growth is occurring (roots/shoots))
- located between phloem and xylem tissues (cambium)
- *pluripotent*
48
What are the uses of stem cells?
- repair of damaged tissues
- treatment of neurological conditions:
- Parkinson's
- Alzheimer's
- developmental biology:
- study of the changes that occur as multicellular organisms grow/develop
49
What are ethical issues surrounding stem cells?
- embryonic stem cells destroys 'life'
- lack of consent
