Cell Division Flashcards
1
Q
What is the cell cycle?
A
Sequence of events between one cell division and the next
2
Q
Outline the stages of the cell cycle
A
- Interphase is the longest phase
- Interphase includes G1, S and G2
- In G1 and G2 cell performs normal functions, organelles are replicated and checks are
made to ensure replication has occurred correctly - DNA replicates in S phase
- Mitosis is when nucleus divides
- Stages of mitosis - prophase, metaphase, anaphase, telophase
- Cytokinesis occurs - division of cytoplasm
3
Q
Which phase usually takes the most time in the cell cycle?
A
Interphase
4
Q
During which stage does the cell surface area to volume ratio decrease?
A
Interphase
5
Q
Describe what happens in G1
A
G1 phase
- Cell synthesises mRNA and proteins required for DNA replication
- Some organelles copied
- Cell increases in size
6
Q
Describes what happens in S phase
A
S phase
- Genetic material replicated (DNA replication)
7
Q
Describes what happens in G2
A
G2 phase
- Additional growth and organelle replication
- Cytoskeleton dismantled
- DNA replication checked for errors
8
Q
Describe what happens during G0
A
Cell leaves cell cycle due to:
- Differentiation - cell becomes specialised
- DNA damage - cell ‘dies’ (apoptosis)
9
Q
How is the cell cycle controlled?
A
Checkpoints at end of each stage of interphase
10
Q
Describe the checkpoints that occur during the cell cycle
A
G1 checkpoint
- End of G1 phase
- Check for cell size, nutrients, growth factors, DNA damage
- If anything wrong, cell enters G0
G2 checkpoint
- End of G2 phase
- Check for cell size, correct DNA replication, cell damage
Spindle assembly checkpoint
- During metaphase of mitosis
- Check for chromosome attachment to spindle
11
Q
Describe the structure of a chromosome
A
- Made up of two sister chromatids
- Joined at the middle by a centromere
12
Q
Summarise the stages involved in mitosis
A
- Step 1: Prophase
- Step 2: Metaphase
- Step 3: Anaphase
- Step 4: Telophase
13
Q
Describe the stages in prophase
A
- Chromosomes condense (become visible under light microscope)
- Nuclear envelope breaks down
- Spindle microtubules extend from centrioles at two ends of the cell to its equator
14
Q
Describe the stages in metaphase
A
- Sister chromatids of each chromosome attach to the spindle microtubules
- Via the centromere
- Line up at equator of cell
15
Q
Describe the stages in anaphase
A
- Centromeres divide
- Chromosomes start to migrate to opposite poles of cell
16
Q
Describe the stages in telophase
A
- Chromosomes reach opposite poles of the cell
- Spindle microtubules break down
- Nuclear envelope reforms
17
Q
Define cytokinesis
A
Division of cytoplasm to form two daughter cells
18
Q
Explain how cytokinesis occurs in animal cells
A
- Microtubules form ring around centre of cell
- Microtubules constrict, forming a cleavage furrow
- Cell eventually pinched in two, forming two genetically identical daughter cells
19
Q
Explain how cytokinesis occurs in plant cells
A
- New cell wall produced across the equator of cell from vesicles containing carbohydrates
- Vesicles fuse together to form cell plate, which fuses with existing cell wall
- There is plasma membrane either side
- Cell divides into two to form two genetically identical daughter cells
20
Q
What is the product of one round of mitosis?
A
Two genetically identical daughter cells
21
Q
Why is mitosis necessary in living organisms?
A
- Growth, replacement and repair of tissues
- Asexual reproduction
22
Q
Why do prokaryotes not divide by mitosis?
A
- No nucleus
- Reproduce by binary fission
23
Q
Define fertilisation
A
Fusion of a male (sperm) and female (egg) gamete
24
Q
Define homologous chromosomes
A
- Pair of chromosomes
- Position of the genes on each chromosome is the same
- The alleles may be different
25
What is the same in all parts of homologous chromosomes?
Sequence of genes
26
What is the difference between sister chromatids and chromosomes?
- The DNA molecules formed by replication prior to cell division are called sister chromatids
- After the centromere splits at the start of anaphase, they are individual chromosomes
27
Describe the function of meiosis
- Type of reductive cell division
- Produces genetically varied gametes with a haploid number of chromosomes (n)
- Maintains chromosome number after sexual reproduction
28
Summarise the stages involved in meiosis
- Prophase I & II
- Metaphase I & II
- Anaphase I & II
- Telophase I & II
29
Describe the stages in prophase I
- Chromosomes condense and pair up - the chromosomes in each pair are homologous
- Crossing over between homologous chromosomes occurs before condensation
- Spindle microtubules extend from the two ends of the cell to its equator
- Nuclear envelope breaks down
30
Describe the stages in metaphase I
- Sister chromatids of each chromosome attach to spindle microtubules via the centromere
- Homologous chromosomes randomly assemble at equator of cell (independent assortment)
31
Describe the stages in anaphase I
- Homologous chromosomes pulled to opposite poles (this halves the chromosome number)
- Each chromosome still consists of two chromatids
32
Describe the stages in telophase I
- Sister chromatids arrive at the poles of the cell and decondense
- Nuclear envelope reforms
- After telophase, the cell divides by cytokinesis
33
Describe the stages in prophase II
- Sister chromatids condense and pair up
- No crossing over
- Spindle microtubules extend from the two ends of the cell to its equator
- Nuclear envelope breaks down
34
Describe the stages in metaphase II
- Sister chromatids of each chromosome attach to the spindle microtubules via the
centromere
- Sister chromatids randomly assemble at the equator of the cell (independent assortment)
35
Describe the stages in anaphase II
- Centromeres divide
- Chromosomes move to opposite poles
36
Describe the stages in telophase II
- Chromosomes arrive at the poles of the cell and decondense
- Nuclear envelope reforms
- After telophase, the cell divides by cytokinesis
- Results in four haploid cells
- Each with 23 chromosomes made from a single chromatid
37
What is the end point of the first division of meiosis?
- Separation of homologous chromosomes
- Creating 2 genetically varied haploid cells
38
What is the end point of the second division of meiosis?
- Separation of sister chromatids
- Creating 4 genetically varied haploid cells
39
During which stage of meiosis does crossing over usually occur?
Prophase I
40
How does meiosis promote variation?
- Crossing over of non-sister chromatids in prophase I
- Independent assortment in metaphase I and II
- Second division of meiosis separates alleles further
- Possible combinations of alleles in gametes is 2n
41
Describe two ways in which genetic variation is brought about during meiosis
Crossing over during prophase I
- Homologous chromosomes pair up and sections of non-sister chromatids are
swapped
- Produces chromatids with new combinations of alleles
Random orientation of pairs of homologous chromosomes in metaphase I and II
- For each pair of chromosomes there are two possible orientations when aligned at
equator of cell
Different combinations of alleles can be made in each daughter cell
42
Define bivalent
Pair of homologous chromosomes
43
Define chiasmata
- Physical connection between non-sister chromatids
- Occurs during prophase I
- Hold homologous chromosomes together as a bivalent until anaphase I
- Can result in the exchange of alleles (crossing over)
44
Define recombinant chromosomes
Homologous chromosomes that have exchanged alleles by crossing over
45
Explain how the recombinants are formed during meiosis
- Recombination occurs in prophase I of meiosis
- Homologous chromosomes come together in pairs
- Chiasmata form between non-sister chromatids
- Crossing over takes place
46
Explain how independent assortment of homologous chromosomes in metaphase I leads to variation
- Bivalents are orientated randomly on the equator during metaphase I of meiosis
- Orientation of one bivalent does not affect orientation of other bivalents
- Pole to which allele on one bivalent moves during anaphase I does not affect the pole to
which alleles on another bivalent move
- Independent assortment will not occur if two genes are linked
47
How are gametes responsible for introducing variation?
- Gametes underpin variation within all species which reproduce sexually
- Fertilisation is a random process
- One gamete is from a male, and one from a female
48
Define tissue
A group of cells working together to perform a function
49
Define organ
A group of tissues working together to perform a function
50
Define organ system
A group of organs working together to perform a function
51
Define organism
A group of organ systems working together to perform a function
52
How are specialised tissues produced in multicellular organisms?
- By differentiation
- Some genes in a genome are expressed whilst others are not
53
How are sperm cells specialised for their function?
- Acrosome - contains digestive enzymes
- Helical mitochondrion - produces ATP needed to help sperm swim
- Microtubules - ensure tail beats side to side to propel sperm forwards
- Protein fibres - strengthen tail
- Haploid nucleus - contains 23 chromosomes in humans
- Whiplash tail (flagellum) - propels sperm up vagina
54
How are erythrocytes (red blood cells) specialised for their function?
- Flattened, biconcave shape - increases SA:V ratio
- No nuclei and few organelles - increases space for haemoglobin (carries oxygen)
- Flexible - can squeeze through narrow capillaries
55
How are neutrophils specialised for their function?
- Type of white blood cell
- Multi-lobed nucleus - easier to squeeze through small gaps
- Granular cytoplasm - contains many lysosomes containing hydrolytic enzymes to digest
pathogens
56
How are squamous epithelial cells specialised for their function?
- Line blood vessels
- Flat, smooth and thin - short diffusion pathway
57
How are ciliated epithelial cells specialised for their function?
- Line trachea to ‘waft’ mucus up to the throat
- Hair-like structures - collect and move mucus up the trachea
58
How are palisade cells adapted for their function of absorbing light?
- Lots of chloroplasts - absorb light and carry out
photosynthesis - Rectangular shape - can be packed close
together - Thin walls - increases rate of diffusion of CO2
59
How are root hair cells adapted for their function of absorbing water and minerals?
Long root hairs - increase surface area,
maximises uptake of water and minerals
60
How are guard cells adapted for their function of opening and closing the stomata?
- Found in pairs either side of stomata - Become less swollen when lose water - closes
stomata to prevent further water loss
61
How is cartilage adapted for its function of reducing friction between bones?
Contains fibres of elastin and collagen
62
How is muscle adapted for its function of moving parts of the body?
Contains myofibrils of actin and myosin - allow muscle to contract and relax
63
How is epidermis adapted for its function of covering the surface of leaves?
- Covered by waxy cuticle - reduces water loss - Stomata present - controls gas exchange and
water loss
64
How is xylem tissue adapted for its function of transporting water and ions?
- Cells are dead and hollow - forms tube for water
- Cells strengthened by lignin - provides support for plants
65
How is phloem tissue adapted for its function of transporting sucrose?
Sieve tube elements have few organelles - more
room for transport of sucrose
Companion cells present to provide key
metabolic products for sieve tube elements Sieve plates are perforated - let sucrose through to the next cell
66
What are stem cells?
Undifferentiated cells
67
Define potency
Ability to differentiate into different cell types
68
Define totipotent
- Stem cells that can differentiate into any type of cell
- Including umbilical cord and amnion
- e.g. a fertilised egg or a zygote
Define pluripotent
69
Define pluripotent
Stem cells that can differentiate into all tissue types
- e.g. embryo cells
70
Define multipotent
Stem cells that can differentiate into a range of cells within a specific tissue
- e.g. stem cells in bone marrow differentiate into different blood cells
71
What are the two sources of animal stem cell?
- Embryonic
- Adult e.g. those found in bone marrow
72
Why are stem cells useful in repairing diseased or damaged organs?
- Continuously divide and replicate
- Can differentiate into different types of specialised cell
73
Where are plant stem cells found?
- Meristem tissue
- Present wherever plant is growing e.g. root and shoot tips
- Present in cambium between xylem and phloem
- Produce xylem vessels and sieve tube elements
74
List some potential treatments involving stem cells
- Heart disease - replace damaged muscle tissue
- Type 1 diabetes - replace damaged insulin-producing cells in pancreas
- Parkinson’s disease - replace damaged cells in the brain
75
What is developmental biology?
Study of the changes that occur as multicellular organisms grow and develop
76
What role can stem cells play in developmental biology?
Enable scientists to study differentiation of any type of cell
77
When compared to other body cells, which characteristic of stem cells is the most important for therapeutic uses?
Enable scientists to study differentiation of any type of cell
78
When compared to other body cells, which characteristic of stem cells is the most important for therapeutic uses?
Ability to differentiate into different types of specialised cell (potency)
79
Describe some ethical concerns with using embryonic stem cells
- Embryos count as human life
- Embryos are unable to decide if they want to be used in this way
80
Provide arguments for the use of embryonic stem cells
- Early embryos are ‘only’ small balls of cells
- Large embryos used by IVF are never implanted - surely better use is to help save lives
- No nervous system - embryos unable to feel pain
81
Advantages of adult stem cells over embryonic stem cells
- Adults can give consent for use of their stem cells
- No rejection problems
- No death of embryos used to provide stem
cells
