2.1.6 - Cell division Flashcards
(122 cards)
1
Q
What is the cell cycle ?
A
The sequence of events that takes place in a cell to enable growth and repair
2
Q
What are the two main phases of the cell cycle ?
A
- Interphase
- Mitotic phase
3
Q
What does a cell do during interphase ?
A
- Cells carry out their major functions
- Protein synthesis occurs in the cytoplasm
- Organelles grow and divide in the cytoplasm
- Normal metabolic processes (some continue throughout cell division e.g. respiration)
- DNA is replicated and checked for errors in the nucleus
4
Q
What are the three stages of interphase ?
A
- G1 - growth phase 1
- S - synthesis phase
- G2 - growth phase 2
5
Q
What occurs in the G1 phase of interphase ?
A
- Proteins for organelle synthesis are produced ; helicase, polymerase and ligase enzymes are produced
- Organelles are replicated
- The cell increases in size
6
Q
What occurs in the S phase of interphase ?
A
Chromosomes are duplicated in the nucleus
7
Q
What occurs in G2 of interphase ?
A
- Cell continues growth
- Energy stores are increased
- Cell double checks duplicated chromosomes for errors and makes any necessary repairs
8
Q
What is G0 of the cell cycle ?
A
- Phase when cells leave the cell cycle either temporarily or permanently.
- A few types of cells that enter G0 can be stimulated to go back into the cell cycle and start dividing again
9
Q
What can be stimulated to go back into the cell cycle after G0 ?
A
Lymphocytes in an immune response
10
Q
Why might a cell leave the cell cycle?
A
- The cell has differentiated
- The DNA of the cell is damaged and therefore becomes senescent.
- Age. The number of senescent cells increases with age and has been linked with age related diseases.
11
Q
What is senescence ?
A
Senescence is the gradual deterioration of functional characteristics in living organisms
12
Q
What occurs in the G1 checkpoint ?
A
- Checks that chemicals needed for replication are present
- Checks for any damage to DNA before S phase
- Checks for cell size
- Checks that the nutrients required for replication are present
13
Q
What occurs in the G2 checkpoint ?
A
- Checks for cell size
- Checks for DNA replication
- Checks for any errors in the DNA and repairs mistakes
14
Q
What occurs in the spindle assembly checkpoint ?
A
- Checks if spindle fibres are connected to the chromosomes properly
- Checks that the chromosomes have aligned ready for metaphase
15
Q
What is the spindle assembly checkpoint also known as ?
A
It is also known as the metaphase checkpoint - mitosis can not proceed until this checkpoint is passed
16
Q
What are the two parts of the mitotic stage of the cell cycle ?
A
- Mitosis - The nucleus divides
- Cytokinesis - The cytoplasm divides and two cells are provided
17
Q
Define chromatid
A
Two identical copies of DNA (a chromosome)
18
Q
Define sister chromatid
A
Two identical DNA molecules joined by a common centromere
19
Q
Define chromatin
A
Uncondensed DNA which is in complex with histone proteins
20
Q
Define chromosomes
A
Structures of condensed and coiled DNA molecules in the form of chromatin
21
Q
Define homologous pairs
A
- A pair of chromosomes, one maternal and one paternal
- Does not necessarily have the same alleles
22
Q
Define centromere
A
- Region at which two sister chromatids are held together
- Point where mitoticspindle fibresattach to pullsister chromatidsapart duringcell division.
23
Q
Define centrioles
A
Component of the cytoskeleton made of microtubules and associated proteins, involved in the development of spindle fibres
24
Q
What are centrosomes ?
A
Centrosomes are pairs of centrioles and they are the sub-cellular region which organise the cell’s microtubules
25
Why are centrioles important in cell division ?
- During mitosis the spindle fibres start at the centrosomes
| - Spindle fibres are responsible for the movement of chromosomes within the cell
26
Define spindle fibres
A structure made of microtubules and associated proteins that assemble from the centrosome to provide the structure that moves chromosomes.
27
What is mitosis ?
Mitosis is the division of the nucleus into two genetically identical nuclei
28
What are the four stages of mitosis, in order ?
- Prophase
- Metaphase
- Anaphase
- Telophase
PMAT
29
Why is mitosis important ?
- It ensures the two daughter cells produced are genetically identical
- Each cell produced has an exact copy of the DNA present in the parent cell, and the same number of chromosomes
- Growth, repair and replacement of cells in multicellular organisms
- Asexual reproduction by Eukaryotic organisms
30
Why do single celled organisms use mitosis ?
To reproduce asexually
31
What is mitosis in bacteria called ?
Binary fission
32
How is DNA packaged ?
- Wrapped around histone proteins to form chromatin
| - Coiled around more proteins to form chromosomes
33
Why does DNA wrap around histones ?
- Makes it more compact
| - Makes it easy to access
34
What happens in prophase ?
- Chromatin fibres condense into chromosomes
- Nuclear membrane begins to break down and nucleolus disappears
- Each duplicated chromosome appears as two identical sister chromatids joined at their centromeres and, in some species, all along their arms by cohesins
- The mitotic spindle begins to form from centrosomes and the microtubules from them.
35
What happens in early metaphase ?
- The nuclear envelope fragments
- Microtubules extending from each centromere can now invade the nuclear area
- The chromosomes have become even more condensed
- Each of the two chromatids of each chromosome now has a kinetochore
- Centrioles taken to opposite poles for formation of the spindle fibres
- Some of the microtubules attach to the kinetochores
- Non-kinetochore fibres interact with those from the opposite pole of the spindle.
36
What happens in late metaphase ?
- Chromosomes are moved by spindle fibres to line up along the equatorial plate of the cell known as the metaphase plate
37
What happens in anaphase ?
- Cohesin proteins are cleaved allowing the sister chromatids to be pulled apart by spindle fibres
- Daughter chromosomes move towards the poles of the cell as their kinetochore microtubules (spindle fibres) shorten
- The cell elongates as the non-kinetochore microtubules (spindle fibres) lengthen
- Results in two poles of cell having equivalent, and complete, collections of chromosomes.
38
What happens in telophase ?
- Two daughter nuclei form in the cell - nuclear membrane forms
- Nucleoli reappears
- Chromatids are now called chromosomes which become less condensed and more distinct
- Remaining spindle fibres are depolymerised
- Mitosis is now complete.
39
What is cytokinesis ?
Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells
40
What occurs in cytokinesis ?
- The cytoplasm divides and the two identical daughter cells are produced
- Starts in late telophase
- Characterised by the formation of a cleavage furrow, which pinches the cell in two, in animal cells.
41
What happens in cytokinesis of animal cells ?
- A cleavage furrow forms
- Microfilaments form a ring around the edge of the plasma membrane pulling the membrane inwards pinching the cell in two
- The plasma membrane fuses in the middle to form two cells
42
What happens in cytokinesis of plant cells ?
- Vesicles carrying cell membrane and cell wall components assemble along the plane of division
- The cell membrane first forms as vesicles fuse
- Cell walls form alongside
43
Define diploid
Normal chromosome number, two chromosomes of each type inherited from each parent
44
Define haploid
Half the normal number of chromosomes, one chromosome of each type
45
Define gametes
Haploid sex cell produced by meiosis in organisms that reproduce sexually
46
Define zygote
The initial diploid cell formed when the nuclei of gametes fuse during the fertilisation stage of sexual reproduction
47
Define reduction division
- The first cell division in meiosis, the process by which germ cells are formed
- Cell division resulting in the production of haploid cells from a diploid cell
48
Define meiosis
Meiosis is a form of cell division where the nucleus divides twice resulting in a halving of chromosome number and producing 4 haploid cells
49
How many cell divisions occur in meiosis ?
2
50
What occurs in meiosis I ?
- The first division, reduction division, when the pairs of homologous chromosomes are separated into two cells
- Cells are haploid, contain one full set of genes instead of two
51
What are the stages of meiosis I ?
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
52
What happens in prophase I ?
- During prophase I the duplicated chromosomes condense, and homologous chromosomes pair up to form bivalents
- The bivalents are connected lengthwise by proteins and crossing over can occur as chromatids entangle
- A chiasma occurs at each point where a crossover has ocurred
- The nuclear envelope fragments as in mitosis
53
Define bivalent
Homologous chromosomes that are associated in pairs physically held together with at least one crossover
54
Define chiasmata
- An x-shaped region in a homologous pair which denotes where sections of DNA have become entangled and crossed over, break and rejoin
- Singular chiasma
55
What is crossing over ?
A genetic rearrangement between two non-sister chromatids involving the corresponding segments of DNA molecules.
56
How does crossing over lead to genetic variation ?
The genes exchanged can be different alleles so the recombinant chromosomes have different sets of alleles to the original chromatids
57
Define recombinant chromatids
Chromatids with a combination of DNA from both homologous chromosomes formed by crossing over at chiasmata.
58
What happens in metaphase I ?
- Homologous pairs line up with one chromosome in each pair facing each pole
- Orientation of homologous pairs on the midline is random and independent of any other homologous pair
- This is called independent assortment
59
Define independent assortment
The random arrangement of bivalents at the metaphase plate.
60
What can independent assortment lead to ?
Variation
61
How can independent assortment lead to variation ?
Different alleles can face the poles e.g. the maternal or paternal chromosomes can therefore end up at either pole during anaphase.
62
What happens in anaphase I ?
- Breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows homologs to separate
- Spindle fibres pull homologous chromosomes to opposite poles
- Random assortment of alleles as pairs move apart
63
What happens in telophase I ?
- Starts with each half of the cell having a complete haploid set of duplicated chromosomes
- Each chromosome is composed of two sister chromatids; one or both chromatids include regions of non-sister chromatid DNA
- Nuclear envelope reforms
64
When does cytokinesis happen ?
Cytokinesis occurs at the same time as telophase I forming two haploid daughter cells (which are not identical )
65
What occurs in meiosis II ?
- The second division
- The pairs of chromatids present in each daughter cell are separated, forming two more cells
- Four haploid cells are produced
66
What are the stages of meiosis II ?
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
67
What happens in prophase II ?
- The chromosomes, which still consist of two chromatids, condense and become visible again
- The nuclear envelope fragments once again, and spindle fibres form and start to move to the chromatids
68
What happens in metaphase II ?
- Individual chromosomes line up along the metaphase plate as in mitosis
- Independent assortment occurs again, leading to more genetic variation following metaphase II
69
What happens in anaphase II ?
- It results in the chromatids of the individual chromosomes being pulled to opposite poles
- Breakdown of the protein holding the sister chromatids together at the centromeres allows this division
70
What happens in telophase II ?
- Is essentially the same as in mitosis, resulting in the nuclear membrane reforming around chromosomes at each pole
- Cytokinesis occurs simultaneously and results in the division of the cells forming genetically different haploid daughter cells in total
71
What two processes occur in meiosis to introduce genetic variation ?
- Crossing over
| - Independent assortment
72
Besides meiosis, what are the two ways in which variation can be introduced ?
- Random fertilisation
| - Gene mutation
73
How does random fertilisation introduce variation ?
- Each gamete has a unique combination of genes
| - Any of the numerous male gametes can fertilise the egg
74
When does random fertilisation occur ?
When two of the nuclei of two gametes fuse to form a zygote
75
How does gene mutation introduce variation ?
Bases with a gene can be altered during DNA replication
76
Define cell
A single repeating unit of an organism
77
Define tissue
A collection of differentiated cells that have a common function
78
Define organ
A group of tissues that work together to carry out a common function
79
Define organ system
A group of organs that carry out a common function
80
Define specialised
Having particular structure to serve a particular function
81
Define differentiated
- The process by which a less specialised cell develops a distinct form and function
- A cell specialising
82
Why do multicellular organisms need specialised cells ?
- Complex communication in a multicellular organism
- Specialised functions need specialised cells
- To maximise efficiency of processes like absorbing nutrients
83
What features does an erythrocyte have to suit it for its function ?
- Biconcave disk, maximises SA to carry oxygen
- No nucleus, more room for haemoglobin
- Flexible, can squeeze through narrow capillaries
84
What features does a neutrophil have to suit it for its function ?
- Multi lobed nucleus, makes it easier for neutrophils to squeeze through small gaps
- Granular cytoplasm, contains many lysosomes which contain enzymes used to attack pathogens
85
What features does a sperm cell have to suit its function ?
- Mitochondria, supplies the energy needed to swim
- Tail, allows for movement to occur
- Acrosome, contains digestive enzymes which digest protective layers around the ovum
86
What features does a root hair cell have to suit its function ?
Root hairs, increase SA:V ratio to maximise the uptake of water/minerals from the soil
87
What features does a palisade cell have to suit it for its function ?
- Rectangular, packs closely to form a continuous layer
- Chloroplasts are able to move in cytoplasm, so can absorb more light
- Lots of chloroplasts
88
What features does a guard cell have to suit it for its function ?
- Cell wall thicker on inside than the outside, so cell does not change symmetrically as its volume changes
- Gap in the centre, allows gases in and out
89
What are the 4 main categories of tissues in animals ?
- Nerve tissues, adapted to support the transmission of electrical analysis
- Epithelial tissues, adapted to cover body surfaces, internal and external
- Muscle tissues, adapted to contract
- Connective tissues, adapted either to hold other tissues together or as a transport medium
90
What features does squamous epithelium have to suit its function ?
- Made up of squamous epithelial cells
- Very thin due to the flat cells that make it up, 1 cell thin
- Forms the lining of the lungs, allows for rapid diffusion
91
What features does ciliated epithelium have to suit its function ?
-
- Made up of ciliated epithelial cells
- Have cilia that line the trachea causing mucus to be swept away from the lungs
- Have goblet cells, release mucus to trap unwanted particles
92
What features does cartilage have to suit its function ?
- Contains elastin and collagen
- Firm flexible tissue, composed of chondrocyte cells embedded in an extracellular matrix
- Prevents the ends of bones from rubbing together and causing damage
93
What features do muscles have to suit their function ?
Skeletal muscle fibres contain myofibrils which contain contractile proteins
94
What are two tissues in plant cells ?
- Epidermis tissue
| - Vascular tissue
95
What features does the epidermis have to suit its function ?
- Covered by a waxy, waterproof cuticle to reduce the loss of water
- Stomata are present, allow for the movement of CO2, O2 and water vapour
96
What features does the xylem tissue have to suit its function ?
- It is a vascular tissue that is responsible for transport of water and minerals throughout plants
- Composed of elongated dead cells, the walls of these cells are strengthened with lignin, provides structural support
97
What features does the phloem tissue have to suit its function ?
- It is a vascular tissue that is responsible for the transport of nutrients from leaves and stems to parts of the plant where it is needed
- Composed of columns of sieve tube cells separated by perforated walls called sieve plates
98
Define undifferentiated
An unspecialised cell originating from mitosis or meiosis
99
Define potency
The ability of a stem cell to differentiate into different cell types
100
Define totipotent
A stem cell that can differentiate into any type of cell and form a whole organism
101
Define pluripotent
A stem cell that can from all types of tissue but not a whole organism
102
Define multipotent
Can only form a range of cells from a certain cell lineage
103
What are stem cells ?
Undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of an organism
104
What are the characteristics of stem cells ?
- Can repeatedly undergo cell division
- Not adapted to a specific function
- Can give rise to specialist cells
105
What are stem cells used for in the body ?
- Growth
- Development, of an embryo
- Tissue repair
106
What happens after they differentiate ?
They can no longer divide and leave the cell cycle into the G0 phase
107
What happens if stem cells do not divide fast enough ?
The tissues are not efficiently replaced, leading to ageing
108
What happens if stem cells divide too fast ?
They can form masses of cells called tumours which can lead to the development of cancer
109
Where are the sources of stem cells in animals ?
- Embryonic stem cells
- Adult stem cells
- Umbilical cords of newborn babies
110
Where are the sources of stem cells in plants ?
Meristematic tissues
111
Where are meristematic tissues found ?
- In the tips of roots and shoots
| - In phloem and xylem tissues, called the vascular cambium
112
How do cells become specialised ?
- All the cells have the same DNA
- Genes are switched on and off by epigenetics
- Different proteins are produced in the cell
- So the cell can undergo a specialised function due to these proteins in the cell
113
What determines the function of the cell ?
The proteins within it
114
Give an example of where totipotent cells can be found in a human
In a zygote
115
Give an example of where pluripotent cells are found in a human
Blastocyst
116
Give an example of where multipotent cells are found in a human
Blood stem cells
117
What can totipotent cells turn into ?
- A whole organism
| - Extra embryonic tissues such as the amnion and the umbilicus
118
What can pluripotent cells turn into ?
Different types of tissues within an organism
119
What can multipotent cells turn into ?
Various types of cell from the lineage of the tissue they are from
120
How long do erythrocytes live for ?
120 days
121
How long do neutrophils live for ?
6 hours
122
What supplies erythrocytes and neutrophils ?
Bone marrow
