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Biology OCR A > Chapter 6 Cell Division > Flashcards

Chapter 6 Cell Division Flashcards

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1
Q

What is the cell cycle?

A

A highly ordered sequences of events that take place in a cell, resulting in division of the cell, and the formation of two genetically identical daughter cells

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2
Q

What are the stages of the cell cycle?

A

Interphase:
G1
Synthetic Phase
G2

Mitosis
Cytokinesis

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3
Q

Which stage of the cell cycle takes the longest amount of time?

A

G1
The replication of the organelles whilst meeting metabolic requirements is a slow process

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4
Q

What are the stages of mitosis?

A

Prophase
Metaphase
Anaphase
Telophase

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5
Q

What happens at each stage of interphase?

A

G1- Proteins which are required for organelle replication are synthesised. Organelles are duplicated. The cell size increases. Regular activities of the cell also, respiration
S- DNA in the nucleus is replicated
G2- Cell size increases, energy stores increased, duplicated DNA is checked for errors

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6
Q

What is G0?

A

The name given to the phase when the cell leaves the cell cycle

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7
Q

Why might the cell leave the cell cycle?

A

Differentiation- Specialised cells are no longer able to divide as they have a designated role
Damage to the DNA- If the DNA is damaged to the point where it cannot be repaired, it can no longer divide. Reduce Cancer risks.
Cells become senescent after a certain number of divisions.

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8
Q

What are cell checkpoints? What are the main cell checkpoints?

A

Control mechanisms of the cell cycle, verifying if a process at each process
G1, G2, Spindle Assembly/ Metaphase

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9
Q

What does the G1 checkpoint check? What happens if the checkpoint is failed?

A

Checks for Cell Size, Nutrients, Growth Factors, DNA damage

If failed, can either enter G0 and re enter under better conditions, try to repair DNA damage, or potentially apoptosis

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10
Q

What does the G2 checkpoint check? What happens if the checkpoint is failed?

A

Checks for Cell Size, DNA replication, and DNA damage.

If failed, the cell cycle is halted. Damaged DNA is tried to repair. If beyond repair, could undergo apoptosis.

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11
Q

What does the Metaphase checkpoint check? What happens if it is not met?

A

Checks that the spindle fibres are all attached to the chromosomes

If failed, the cell cycle is halted, and will not continue until all the spindle fibres that need to be attached are.

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12
Q

What is the importance of mitosis?

A

Ensures that the two daughter cells are identical to each other and the parent cell
This is useful in:
Growth
Replacement/ Repair of tissues
Asexual Reproduction
Proliferation of white blood cells
Body plans
Producing new stem cells

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13
Q

What is the difference between chromosomes and chromatids?

A

The chromatid is one DNA molecule.
Chromosomes is the whole entity of the DNA molecules. E.g before mitosis, there is one chromatid per chromosomes. But after the initial replication, there are two chromatids joined together by a centromere. This whole structure is still only 1 chromosome.

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14
Q

What happens in prophase?

A

Chromatids coil and condense to form chromosomes, visible under a light microscope.
The nucleolus disappears and the nuclear membrane breaks down. The nuclear envelope disappears.
Two centrioles moves to opposite ends of the poles, which begin to form a spindle fibres cage
The spindle fibres begin to attach to the centromeres of the chromosomes, beginning to move them

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15
Q

What happens in metaphase?

A

Chromosomes are moved to the midline of the cell, along the metaphase plate

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16
Q

What happens in anaphase?

A

The centromeres divide
Chromatids are separated by the shortening of spindle fibres
Sister Chromatids are pulled to opposite poles

17
Q

What happens in telophase?

A

Chromosomes assemble at each pole
The nuclear envelope begins to reform
Chromosomes begin to uncoil
The nucleolus is reformed
Cytokinesis begins- new cell membrane forming

18
Q

What is cytokinesis? How does it occur?

A

Cytokinesis is the physical division of the cell into two separate cells
In animals cells, a cleavage furrow forms around the middle of the cell. The cell surface is pulled inwards, fusing to form two cells
In plant cells, due to cell walls, vesicles from the Golgi assemble along the metaphase plate, vesicles fuse, cell membrane divides, cell wall forms around it

19
Q

What is meiosis? What type of division is it?

A

The division of a cell to form 4, unique, haploid gametes
It is a reduction division

20
Q

What is fertilisation?

A

The fusion of the nuclei of a male and female gamete to produce a zygote which develops into an organism

21
Q

What are homologous chromosomes? How do the chromosomes differ from each other?

A

Matching chromosomes, with the same genes, but may have different alleles

(Genes are the same as they code for the same characteristic , but alleles code specifically how that characteristic will be)

22
Q

What are the main stages in Meiosis Division 1?

A

Prophase 1: Same things in Mitosis. But, homologous chromosomes pair up to form bivalents. Crossing over occurs
Metaphase 1: Same as Mitosis except homologous pairs of chromosomes line up along the metaphase plate. Independent Assortment
Anaphase 1: Homologous chromosomes pulled to opposite poles, sister chromatids still together. Crossed over parts of DNA break apart and rejoin, possibly resulting in an exchange of DNA. Points of Rejoin= Chiasmata, chromosomes now recombinant
Telophase 1: Same as in mitosis.

23
Q

What are the main stages in Meiosis Division 2?

A

Prophase 2: Same as Mitosis
Metaphase 2: Chromosomes align along the metaphase plate. Independent Assortment again due to crossing over
Anaphase 2: Same as Mitosis
Telophase 2: Same process as Mitosis, but results in 4 Haploid Cells

24
Q

How does meiosis introduce genetic variation?

A

Independent Assortment- The arrangement of Homologous Pairs of chromosomes in Metaphase 1 is random. Which cell the maternal or paternal chromosomes ends up in is random. Same process for Metaphase 2 when considering recombinant genes

Crossing Over/ Recombination: Exchange of DNA when sections of DNA break off and rejoin at the chiasmata produce new DNA molecules.

Fusion of which two gametes and which two people (their genome) is random

25
Q

How specifically does metaphase 1 introduce genetic variation?

A

Independent assortment
Homologous chromosomes are genetically different, different alleles
When lining up upon the midline of the cell, metaphase plate, Maternal/paternal chromosomes orientation is random, which pole of the cell they end up in is random

Biology OCR A (42 decks)

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