12 Biology > Cell division > Flashcards

Cell division Flashcards

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1
Q

What’s a centromere

A

A specialized sequence of DNA where the sister chromatids are attached to each other

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2
Q

Why might a cell enter G0

A

Its been specialized through cell differentiation
Once a checkpoint identifies cell damage

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3
Q

How is DNA composed in the nucleus?

A

Wrapped around histone proteins to form DNA-Histone complexes and is compacted into structures called chromatin.

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4
Q

Why does DNA usually exist as chromatin?

A

Because it makes it easier for DNA replication to occur as the loosely coiled threads of chromatin make it easy for parts to unwind and for transcription to occur.

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5
Q

What happens to chromatin during cellular division

A

The chromatin condenses into tightly packaged chromosomes.

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6
Q

Why does chromatin condense into chromosomes during cellular division

A

This is essential for proper segregation of genetic material during cell division and prevents DNA from tangling and damaging. Also enables spindle fibers to attach effectively to chromosomes

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7
Q

Whats the 3 phases of the cell cycle

A

Interphase
Nuclear division
Cytokinesis/cell division

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8
Q

Whats apoptosis

A

Programmed cellular death

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9
Q

Whats G0

A

The name given to the stage where the cell moves out of the cell cycle. This happens due to differentiation or when the DNA becomes damaged so cell division is no longer viable. It can be temporary or permanent depending on the signal the cell gets

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10
Q

Whats the 3 interphase stages

A

G1, S phase and G2

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11
Q

Whats G1

A

During G1 the cell prepares to replicate DNA. There is a lot of transcription (synthesis of mRNA) and translation (synthesis of proteins) in order to enable DNA replication. The cell usually grows larger and some organelles are copied as well. There is a checkpoint to check for DNA damage before the cell commits to replicate the DNA

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12
Q

Whats S phase

A

During the S phase, chromosomes are copied by the process of DNA replication. The process of replication generates sister chromatids. Sister chromatids are attached to each other by a centromere. A centromere is a specialised sequence of DNA that links the sister chromatids and is important for throughout mitosis. 2 sister chromatids make up 1 chromosome.

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13
Q

Whats G2

A

During G2 the cell undergoes additional growth, replenishes energy stores and dismantles the cytoskeleton. G2 ends with mitosis, nuclear division begins. There is another checkpoint to ensure the chromosomes have been replicated correctly

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14
Q

Wheres the 3 checkpoints in the cell cycle

A

During G1
During G2
During metaphase

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15
Q

Whats the purpose of the checkpoint in G1

A

To check for DNA damage before the cell commits to replicate the DNA

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16
Q

What’s the purpose of the checkpoint in G2

A

At the end of G2 to ensure the chromosomes have been replicated correctly

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17
Q

Why is it incorrect to say after the S phase and the replication of DNA, that the chromosomes have been doubled

A

Because chromosomes are counted by the number of centromeres not the amount of DNA

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18
Q

Why can’t you say the number of chromosomes have doubled after interphase

A

Because the product of interphase doesn’t produce more chromosomes it just means that the chromosomes are now composed of 2 sister chromatids

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19
Q

What does produce 2 genetically identical daughter cells

A

Mitosis

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20
Q

Whats the acryonym for mitosis phases

A

PMAT

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21
Q

Explain the P in PMAT

A

Prophase

Nuclear envelope disintegrates and we can no longer see the nucleolus as it shrinks. Chromosomes condense (thicken and shorten) and become more visible as they pick up the stain more intensely. Centrioles migrate to opposite ends of the cell.

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22
Q

Explain the M in PMAT

A

Metaphase

Chromosomes are moved by the spindle fibres and moved to line up along the equator/middle of the cell. There is a checkpoint here to ensure the spindle fibres have attached correctly

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23
Q

Explain the A in PMAT

A

Anaphase

They split at the centromere, as spindle fibres move chromatids. Sister chromatids separate to opposite poles of the cell (centromere moves first – hence the distinctive V shape). Each pole of the cell receives one chromatid from each chromosome

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24
Q

Whats the T in PMAT

A

Telophase

Separated sister chromatids are now in 2 groups at opposite ends of the cell. Chromosomes decondense and start to become less visible. The spindle fibres break down and a nuclear envelope starts to reform around each set of chromosomes

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25
Explain cytokinesis of animal cells
In animal cells, both cell membranes and cytoplasm divide/split. Forming 2 genetically identical daughter cells. The cleavage furrow is the indentation of the cells surface that begins the progression of cytokinesis
26
Whats the cleavage furrow
The indentation of the cells surface that begins the progression of cytokinesis
27
Explain the cytokinesis of plant cells
In plant cells, they can’t divide like animal cells because they have a cell wall and are too stiff. Instead vesicles from the Golgi apparatus form membrane structures down the centre of the cell which fuse together to form a central cell membrane. A new cellulose cell wall also has to form.
28
Whats produced in meiosis
4 genetically diverse haploid cells
29
When does crossing over occur
During meiosis 1, in prophase 1
30
Whats a homologous chromosome
A chromosome pair which are the same size, with the same genes in the same position
31
What’s the point that the non sister chromatids overlap at during crossing over
Chiasmata
32
What’s a bivalent
The structures that the homologous chromosomes form during crossing over
33
Why does crossing over take place
DNA is exchanged between the chromosomes. They create genetic variation
34
What’s the products of crossing over called
Recombinant chromatids which are genetically distinct from each other.
35
What’s independent assortment
It’s the random sorting of chromosomes in a line during metaphase meaning that there’s the genetic variation in gametes produced.
36
What’s the mitotic index
The mitotic index is a measure of the proportion of cells which are undergoing the mitotic phase.
37
When does crossing over take place
During prophase 1 of meiosis
38
What happens during the first cycle of meiosis
• Prophase I – Chromatin condenses, the nuclear envelope disintegrates and centrioles migrate to poles of the cell and spindle fibres begin to form.Chromosome match up with their homologous pairs, this means they are the same size with the same type of genes in the same place. Crossing over also takes place, this means that recombinant DNA which has variation are produced. • Metaphase I – Here, there is independent assortment of the chromosomes as they line up in their pairs along the middle of the cell. Independent assortment refers to the maternal or paternal being randomly on either side of the equator. Spindle fibres attach to the centromeres. • Anaphase I – Here the homologous chromosomes are pulled apart from their bivalents by the spindle fibres at the poles. • Telophase I – Maternal or paternal chromosomes have now ended up in either of the new cells. Nuclear envelopes reform, chromosomes decondense and cells undergo cytokinesis. There are now 2 varied diploid cells formed.
39
What happens during the second cycle of meiosis
• Prophase II – Chromosomes re-condense and the nuclear envelope breaks down again. Spindle fibres reform and there is no crossing over. • Metaphase II – The chromosomes line up in a single line rather than their previous homologous pairs. Here there is second independent assortment, this is variation on which direction that the chromatids are facing, this is random. Spindle fibres now attach at the centromere. • Anaphase II – Centromeres are split apart by the spindle fibres and the chromatids move to the poles of the cells. This is the same as anaphase in mitosis. • Telophase II – Chromosomes decondense and a nuclear envelope reforms. The cell undergoes cytokinesis and 4 haploid genetically diverse daughter called have been produced.
40
Why’s it important that gametes have a haploid number of chromosomes
So that diploid number of chromosomes is restored when the gametes fuse. It prevents doubling of chromosome number
41
Whats the 2 defining features of stem cells
It can divide an unlimited number of times It can differentiate into a specialised cell
42
What does a cell enter due to differentiation?
G0 in the cell cycle. It means they can no longer divide
43
What’s the 3 types of potency stem cells
Totipotent Pluripotent Multipotent
44
Describe Totipotent stem cells
Totipotent stem cells are stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (the cells that make up the placenta)). These are found in the zygote formed when a sperm cell fertilises an egg cell, up to the 16-cell stage of human embryo development
45
Describe pluripotent stem cells
Pluripotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into any cell type found. In an embryo but are not able to differentiate into extra-embryonic cells.
46
Describe multipotent stem cells
Mulitpotent stem cells are adult stem cells that have lost some of the potency associated with embryonic stem cells and can only differentiate into a limited range of cell types.
47
Describe bone marrow stem cells
They can be obtained and used through bone marrow transplants. They’ve been successful in replacing faulty bone marrow that produced abnormal blood cells. However the cells cannot develop into all cell types that pluripotent can do and therefore are limited use.
48
Describe embryonic stem cells
Can be used to treat diseases such as neurological conditions. They could even grow new organs and tissues. This can improve and save lives. Although this is controversial as stem cell extraction destroys embryos and therefore a potential life. There is also the risk of the cells dividing uncontrollably or risk rejection by the body’s immune system.
49
Describe induced pluripotent stem cells
Induced pluripotent are stem cells created in a lab from specialised adult cells and reprogramming them to become pluripotent. This could allow adult cells to become as potent as pluripotent embryonic stem cells and could be obtained from adult donors without the same ethical issues. In this way, tissues and organs could then be genetically identical to the patient, reducing risk of rejection and the need for immunosuppressant drugs.
50
How has stem cell advancement aided biological knowledge
We can now understand how cells function Testing on new drugs and there effectivity as well as side effects
51
Where do does cell division and where do stem cells come from in plants
In the meristem Never say that there are meristem cells, always say cells found in the meristem
52
Where can you find meristem regions in plants
In tips of shoots and roots in plants mainly Also some found between the phloem and xylem tissues. These can form xylem vessels and phloem sieve tubes
53
How can meristem tissue cuttings be used in biological research
Creates clones of plants quickly and economically. Acid rare and endangered species of plants and preserve the plant species.
54
Describe the function and adaptations of Erythrocytes
Carry oxygen from the lungs to respiring cells Very small and biconcave shape so large SA/V ratio. Flexibility allows for it to easily reach all regions of the cell Most of their organelles are lost at differentiation, provides more space for haemoglobin molecules housed inside them. Contains haemoglobin which binds to oxygen
55
Describe the function and adaptations of Neutrophils
Ingest invading pathogens - phagocytosis They are attracted to and travel towards infection sites by chemotaxis. Contain many lysosomes with enzymes to digest pathogens Can change shape to engulf pathogens
56
Describe the function and adaptations of Squamous epithelial cells
A lining tissue thats forms thin surfaces for diffusion– In the capillaries and alveoli Flattened in shape to reduce diffusion distance Smooth surface allows rapid movement of substances Form a single layer to maximise diffusion rate
57
Describe the function and adaptations of Ciliated epithelial cells
A lining tissue that’s moves substances– In the intestines, trachea, oviducts Cilia beat in coordinated wave to move materials Many mitochondria to provide ATP for movement High surface area to volume ratio
58
Describe the function and adaptations of sperm cells
To travel along the ovaries and fuse to fertilise an egg cell Many mitochondria to carry out aerobic respiration for energy Small but long and thin – Streamline Releases enzymes from the acrosome in its head that digest the outer protective covering of the ovum The head of the sperm contains the haploid male gamete to restore diploid number after fertilisation
59
Describe the function and adaptations of palisade cells
To carry out photosynthesis within leaves They are long and cylindrical so they can pack together quite closely with a little space for air to circulate They contain many chloroplasts They have a large vacuole so the chloroplasts are positioned nearer to the periphery of the cell, reducing the diffusion distance They contain cytoskeleton threads and moto proteins to move chloroplasts to where sunlight levels are higher
60
Describe the function and adaptations of root hair cells
Absorption of water and mineral ions from soil The hair like projection greatly increases the SA for absorption of water and mineral ions Thin walls reduces the diffusion distance Many mitochondria for the production of ATP used for active transport Large vacuole maintains water potential gradient
61
Describe the function and adaptations of guard cells
Control gas exchange and water loss by opening and closing stomata Unevenly thickened cell walls cause cells to blend when turgid Contains chloroplasts to produce ATP Can change turgidity to open and close stomata
62
Describe the function and adaptations of Squamous epithelium
Provides a thin surface for diffusion and exchange Consists of flattened cells, reducing diffusion distance – 1 cell thick Smooth surface allows for efficient movement of substances Closely packed cells prevent leakage
63
Describe the function and adaptations of Ciliated epithelium
Move substances along surfaces Cilia beat in a coordinated manner to move material in one direction Many mitochondria produces ATP for beating Often associated with goblet cells that secrete mucus
64
Describe the function and adaptations of Cartilage
Provides support, flexibility and shock absorption Chondrocytes embedded in a firm but flexible matrix Matrix contains collagen fibres for strength Smooth surface reduces friction at joints Flexibility allows bending without breakage
65
Describe the function and adaptations of Muscle
Contracts for movement Long muscle fibres can shorten for contraction Contain actin and myosin filaments that slide past each toner Many mitochondria provide ATP for contraction Good blood supply to deliver oxygen and glucose
66
Describe the function and adaptations of xylem
In the vascular bundle of a plant Transports water and mineral ions from roots to shoots Dead cells (lignin) with hollow lumen reduces resistance for water flow Thick walls provide structural support Continuous column allows for mass flow of water Pits allow lateral movement of water
67
Describe the function and adaptations of phloem
In the vascular bundles of plants Transports organic substances by translocation Sieve tube elements form continuous tubes for mass flow Sieve plates allow the movement of solvents between cells Contains mitochondria for active loading of sucrose
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