Biology > 6 - Cell division > Flashcards

6 - Cell division Flashcards

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1
Q

phases of the cell cycle

A

Interphase
-> G1
——> G1 checkpoint
-> S
-> G2
——> G2 checkpoint

Mitotic phase
-> mitosis
——-> spindle assembly checkpoint
-> cytokinesis

G0

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2
Q

interphase

A

long periods or growth and normal working , where the cell is carrying out its major functions
-> G1 - first growth phase
-> S - synthesis phase
-> G2 - second growth phase

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3
Q

during interphase

A
  • DNA is replicated and checked for errors in the nucleus
  • protein synthesis
  • mitochondria grow and divide, increasing in number
  • chloroplast grow and divide in plant and algal cell
  • normal metabolic processes occur - respiration
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4
Q

stages of interphase

A

G1 - the first growth phase: proteins from which organelles are synthesised are produced and organelles replicate, cell increases in size
s - synthesis phase: DNA is replicated in the nucleus
G2 - second growth phase : cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors

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5
Q

mitotic phase stages

A
  • mitosis - nucleus divides
  • cytokinesis - cytoplasm divides and two daughter cells produce
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6
Q

what is G0

A
  • the name for when the cell leaves the cycle, either temporarily or permanently
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7
Q

why would a cell go into G0

A
  • differentiation - a cell that becomes specialised to carry out a particular function is no longer able to divide. it will carry out this function indefinitely and not enter the cell cycle again
  • DNA of a cell may be damaged, if so it is no longer viable, therefore it wont divide and enters a period of permanent cell arrest (G0)
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8
Q

Control of the cell cycle

A

checkpoints are the control mechanism of the cell cycle- they monitor and verify whether the processes at each phase have been carried out accurately before the cell progresses onto the next phase

it ensures the fidelity of cell division

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9
Q

what are the checkpoints of the cell cycle

A

G1 Checkpoint (Restriction Point):

This checkpoint occurs at the end of the G1 phase before the cell enters the S phase.
It assesses whether the conditions are favourable for DNA replication to proceed.
If conditions are not suitable it enters G0

G2 Checkpoint:

This checkpoint occurs at the end of the G2 phase before the cell enters the M phase (mitosis).
It ensures that DNA replication has been completed accurately and that the cell is ready for mitosis.
If DNA damage is detected , the cell cycle may be halted

Spindle Assembly Checkpoint:

This checkpoint occurs during metaphase, after the chromosomes have aligned at the metaphase plate but before the sister chromatids separate.
It monitors the attachment of spindle fibres to the kinetochores of sister chromatids.
If all chromosomes are not properly attached to the spindle apparatus, the cell division process is delayed until proper attachment is achieved, preventing errors in chromosome segregation.

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10
Q

why is mitosis important

A

ensures that both daughters produced are genetically identical
- each have the exact copy of DNA present in the parent cell and have the same number of chromosomes
- growth replacement and repair of tissues
- necessary for asexual reproduction
-

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11
Q

chromosome structure and subsets

A

before replication:
one chromosome has one chromatid

after replication:
one chromosome has two chromatids

after mitotic division:
one chromosome has one chromatid

centromere is where two sister chromatids are joined
together

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12
Q

stages of mitosis

A

prophase
metaphase
anaphase
telophase

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13
Q

Prophase

A
  • Chromatin condenses into visible chromosomes.
  • The nucleolus becomes less distinct or disappears entirely
  • nuclear envelope/membrane breaks down.
  • spindle formation begins
    centrioles migrate to opposite poles
  • spindle fibres attach to centromeres and start to move chromosomes
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14
Q

metaphase

A

chromosomes are moved by the spindle fibres to form a plane at the centre of the cell, called the metaphase plate, and then held in position

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15
Q

anaphase

A
  • centromeres divide
  • chromatids are separated and pulled to opposite poles by shortening spindle fibres
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16
Q

telophase

A
  • chromatids reach the poles and are now called chromosomes
  • nuclear envelop forms around each chromosome
  • chromosomes start to uncoil and the nucleolus if formed
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17
Q

cytokinesis in animals

A
  • a cleavage furrow forms around the middle of the cell
  • the cell-surface membrane is pulled inwards by the cytoskeleton, until its close enough to fuse around he middle forming two cells
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18
Q

cytokinesis in plant cells

A
  • cant form cleavage furrow as cell wall is too strong
  • vesicles from Golgi apparatus assemble at the centre of the cell
  • they fuse together as well as the cell surface membrane- forming two cells
  • new sections of the cell wall form along the new sections of the membrane
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19
Q

what is meiosis

A

the nucleus divides twice to form 4 daughter cells which contain half the number of chromosomes than the parent cell- haploid

  • this is to form gametes
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20
Q

what are homologous chromosomes

A

are pairs of chromosomes that contain similar genetic information.

They are inherited, one from each parent, and are similar in size, shape, and gene sequence.

Homologous chromosomes carry alleles for the same genes at the same loci, but these alleles may be different variants (alleles) of the gene.

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21
Q

allele

A

different versions of the same gene - have the same locus

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22
Q

stages of meiosis

A

meiosis I - firs division where the homologous chromosomes are separated into two cells

meiosis II - second division the pairs of chromatids are separated forming two more cells- 4 haploid cells are produced

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23
Q

Meiosis I

A

Prophase I
Metaphase I
Anaphase I
Telophase I

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24
Q

Meiosis II

A

Prophase II
Metaphase II
Anaphase II
Telophase II

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25
Prophase I
chromosomes condense, nuclear envelope disintegrates, nucleolus disappears and spindle formation begins -homologous chromosomes pair up to form bivalents - crossing over also occurs- the exchange of genetic material between homologous chromosomes
26
metaphase 1
- homologous pairs assemble along the metaphase [;ate - independent assortment happens - the orientation of each homologous pair is random and independent. this results in genetic variation
27
Anaphase 1
- homologous chromosomes are pulled to opposite poles and the chromatids stay joined together - sections of DNA on the chromatids which became entangle during crossing over break off and rejoin - resulting in the exchange of DNA - the point where the chromatids break and rejoin is called chiasmata - this forms recombinant chromatids, with genes being exchanged, which could be different alleles of the same gene, meaning the alleles are different from the original chromatid genetic variation arises
28
telophase 1
chromosomes assemble at the poles and the nuclear membrane reforms, chromosomes uncoil cell undergoes cytokinesis and divides into two cells haploid cells form
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Prophase II
chromosomes condense and become visible nuclear envelop breaks down and spindle formation begins
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metaphase II
individual chromosomes line up on metaphase plate independent assortment and genetic variation
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anaphase II
chromatids of the individual chromosomes are pulled to opposite poles after division of centromeres
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telophase II
chromatids assemble at the poles chromosomes uncoil to form chromatin nuclear envelop forms and nucleolus is visible cytokinesis to form 4 daughter haploid cells -> they are genetically different from each other and the parent cell (due to crossing over and independent assortment
33
Crossing Over
Bivalents develop. Homologous chromosomes come together to form bivalents. Chiasmata form. Non-sister chromatids wrap around each other, and they join up at certain points (called chiasmata) Chromosomes break. The chromosomes can break up at the chiasmata, and sections of chromosomes may swap over between non-sister chromatids. The swapping over is only between non-sister chromatids. Recombination occurs. The final chromatids still have the same genes, but they may have different alleles
34
Independent Assortment
independent assortment means that each chromosome is inherited randomly and independent of other chromosomes In meiosis II, each pair of homologous chromosomes is split up. Remember, in any cell the homologous pair consists of two chromosomes which may or may not be identical. When the pair splits up, each daughter cell will receive one chromosome. The allocation of this is completely random – hence we call it independent assortment.
35
Why is meiosis important for producing variation?
Meiosis is important for producing variation because it shuffles the genetic material in a way that leads to the formation of new combinations of alleles, or different versions of genes. This variation contributes to the diversity of traits found in a population and is an important mechanism for the evolution of species.
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How does meiosis contribute to evolution?
Meiosis contributes to evolution by producing genetic variation that can be selected by natural selection. This variation allows species to adapt to changing environments and helps to drive the process of evolution over time
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erythrocytes
- flattened biconcave shape = increases surface area - in mammals they don't have a nucleus = increases space for haemoglobin - flexible = able to squeeze through narrow capillaries
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Neutrophils
- role in the immune system - multi-lobbed nucleus= easier to squeeze through gaps to get to the site of infection - granular cytoplasm contains many lysosome that contain enzymes used to attack pathogens
39
sperm cell
- male gametes - deliver genetic info to the female gamete - tail/flagellum so they are capable of movement - contain any mitochondria to supply the energy to swim - acrosome in top of head contains digestive to digest layers of the ovum and let the sperm penetrate and fertilise
40
Palisade cell
- present in mesophyll - contains chlorophyll to absorb large amounts of light for PHS - rectangular and can be closely packed to form a continuous layer - thin cell walls = increase ROD - chloroplasts can move in cytoplasm to absorb more light
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root hair cells
- present in the surfaces of the roots near growing tips - have long extension called root hairs = increase surface area for RO movement
42
Guard cells
- on the surfaces of leaves and form the stomata - necessary for CO2 to enter for PHS - when they lose water they become less swollen and change shape and the stomata closes to prevent water loss - cell wall of guard cell is thicker on one side so they cell doesn't change shape symmetrically
43
main categories of tissue in animals
- nervous tissue - adapted to support the transmission of electrical impulses - epithelial tissue - adapted to cover surfaces - muscle tissue - contraction - connective tissue - adapted to hold tissues together or as a transport material
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squamous epithelium
- made of squamous epithelial cells - flat - very thin due to the flat cells that make it up- one cell thick - to increase ROD - forms the lining of the lungs - basement membrane
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ciliated epithelium
- made of ciliated epithelial cells -have hair like structures called cilia that move in a rhythmic manner - it lines the trachea - has goblet cells that release mucus to trap any unwanted particles in the air
46
cartilage
- a connective tissue found in outer ear, nose and between bones - contains fibres of elastin and collagen' - t is a firm, flexible connective tissue made of chondrocyte cells embedded in an extra cellular matrix - prevent bones from rubbing together and causing damage
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muscle
- tissue needs to shorten in length to move bends - skeletal- contains myofibrils
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types of tissue in plants
- epidermis - covers the plant - vascular tissue - adapted for transport of water and nutrients
49
epidermis
- single layer that covers the surface of plants - closely packed cells - covered by a waxy, waterproof cuticle to reduce the loss of water - contains pairs of guard cells that form the stomata which can open close allowing CO2 O2 and H2O in and out
50
xylem
a vascular tissue that transports water and minerals throughout plants - composed of dead elongated cells strengthened with lignin which provides structural support
51
phloem tissue
vascular tissue transports organic nutrients like sucrose from the leaves and stems where it is made by PHS to other areas - made of sieve tubes cells separated by perforated walls called sieve plates
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organ
collection of tissues that are adapted to perform a particular function un organism
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organ systems
composed of a number of organs working togehter to carry out a major function in the organism
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differentiation
the process of a cell becoming specialisd -> it involves the expression of some genes but not others in the cells genome
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undifferentiated cells
- cells begin as this (after mitosis and meiosis) - not adapted for a particular function - have the potential to differentiate to become any type of cell - called stem cells
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stem cell potency
-the ability of a stem cell to differentiate into different cells - greater the number of cells it can differentiate into, the greater the potency totipotent pluripotent multipotent
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totipotent
stem cells that can differentiate into any type of cell - a fertilised egg/ zygote
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pluripotent
stem cells can form all tissue types but not organisms - present in early embryos and are the origin of the different type of tissue within the organism
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multipotent
stem cells that can only form a range of cells within a certain type of tissue Haematopoietic cells in bone marrow
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replacement of RBC and WBC
- have no nucleus so and lack of organelles so have a short lifespan - so need to be replaced constantly - stem cell colonies in bone marrow produce large amounts or RBC - WBC last for 6hrs RBC las 120 days
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sources of stem cells
- embryonic - tissue
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embryonic stem cells
- cells present at early stages of embryo development - totipotent - after 7 days a mass of cells- blastocyst has formed and cells ow pluripotent
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tissue stem cells
- present throughout life - found in specific areas like bone marrow - multipotent - or the umbilical cord
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sources of plant stem cells
- present in meristematic tissue - found in roots and shoots (apical meristems) - also found between the phloem and xylem - the vascular cambium -> cells here differentiate into into cells in the xylem and phloem - pluripotent
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