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AS Human Biology > Chapter 8 - Cell Division > Flashcards

Chapter 8 - Cell Division Flashcards

(67 cards)

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1
Q

What is the name of the process by which cells divide to make exact copies of themselves?

A

Mitosis

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2
Q

How is DNA organised in eukaryotic cells?

A

Into chromosomes

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3
Q

How many chromosomes do human cells have?

A

46

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4
Q

Why can’t you see chromosomes when a cell isn’t dividing?

A

The DNA is ‘unwound’ and spread out in the nucleus

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5
Q

What phase is a cell in if it isn’t dividing?

A

Interphase

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6
Q

What is chromatin?

A

DNA molecule wrapped around histones (proteins)

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7
Q

When does DNA replicate?

A

In interphase

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8
Q

What happens to chromatin when a cell starts to divide?

A

It coils up and folds to form chromosomes

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9
Q

What does a chromosome look like in prophase?

A

It has two sister chromatids, held together by a centromere

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10
Q

Why are there two chromatids?

A

The DNA replicated in interphase

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11
Q

What does the cell do in interphase?

A

Protein synthesis
Cell organelle replication
Respiration

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12
Q

What is interphase divided into?

A

G1, S and G2

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13
Q

What happens in growth phase 1 (G1)?

A

Cell organelle synthesis

Biochemicals produced

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14
Q

What happens in synthesis (S) phase?

A

DNA is replicated

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15
Q

What happens in growth phase 2 (G2)?

A

Energy stores are increased

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16
Q

What are the four phase of mitosis?

A

Prophase
Metaphase
Anaphase
Telophase

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17
Q

What happens in prophase?

A

Chromosomes shorten and thicken
Spindle fibres form
Nuclear envelope disintegrates

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18
Q

What happens in metaphase?

A

Chromosomes are arranged on the equator

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19
Q

What happens in anaphase?

A

Chromosomes migrate to opposite poles

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20
Q

What happens in telophase?

A

Spindle fibres disintegrate

Nuclear envelope develops

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21
Q

What is mitosis important for?

A

Growth
Repair
Asexual reproduction

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22
Q

Explain the importance of mitosis in growth

A

Zygotes are diploid
The chromosomes contain all the information needed to make a whole new organism
The zygote divides by mitosis to ensure every cell has the exact same alleles

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23
Q

Explain the importance of mitosis in repair

A

If cells die or are damaged, they need to be replaced by cells with exact same genetic information as them

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24
Q

Explain the importance of mitosis in

A

All the offspring are identical to the one parent
This is advantageous if environmental conditions aren’t changing
It enables one organism to produce offspring very quickly

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25
Explain what happens in prophase in detail
Chromosomes become visible Centrioles (organelle) move to the poles of the cell They send out microtubules (fibres) which form a system called the spindle
26
Explain what happens in metaphase in detail
The centromeres of the chromosomes attach to the equator of the spindle Centromeres divide The chromatids can be called daughter chromosomes
27
Explain what happens in anaphase in detail
Microtubules attached to the centromeres contract | Daughter chromosomes are pulled to the opposite poles
28
Explain what happens in telophase in detail
Daughter chromosomes reach their poles They unwind to become longer and thinner Spindle fibres break down Nuclear membrane reforms The centrioles divide so each daughter cell can have two The cytoplasm constricts, separating the cell in two
29
What is a tumour?
A mass of cells that have divided too many times
30
What types of tumour are there?
Benign and malignant
31
Describe benign tumours
``` Slow-growing Stay in one tissue Do not spread to other parts of the body Not usually life-threatening When removed, they do not grow back ```
32
Describe malignant tumours
Grow rapidly Invade surrounding tissues Cells can break off from the main tumour Life-threatening unless treated early
33
What are proto-oncogenes?
Genes that stop cells dividing by mitosis too often
34
What is one way a proto-oncogene can work?
Coding for receptor proteins These are then activated by growth factor This switches the genes on to stimulate DNA replication (hence cell division)
35
How else can proto-oncogenes work?
They produce the growth factor needed to stimulate cell division
36
When do proto-oncogenes become oncogenes?
When the base sequence changes; a mutation occurs
37
Describe one way how oncogenes cause uncontrolled cell division
They can produce a different form of receptor protein that stimulates cell division even without growth factor
38
How else can oncogenes cause uncontrolled cell division?
They can produce uncontrolled amount of growth factor
39
What are tumour suppressor genes?
Genes that code for proteins that stop cells dividing | Also, they cause cells with damaged DNA to die
40
What would happen if a tumour suppressor gene mutated?
The cell might carry on dividing uncontrollably, passing on damaged DNA
41
What is a primary tumour?
A mass of cells that has become large enough to develop its own blood and lymph vessels in one place
42
What is a secondary tumour?
When cells from the primary tumour break off and spread into blood and lymph vessels They travel around the body and cause new tumours in other parts of the body - secondary tumours
43
What is the name for the spreading of tumour cells?
Metastatis
44
What are secondary tumours also known as?
A metastatis
45
What are the causes of cancer?
``` Genetic factors Age Ionising radiation UV radiation Chemicals Viruses ```
46
How can genetic factors cause cancer?
Some people have proto-oncogenes which are more likely to mutate This is why it can run in families
47
How does age affect getting cancer?
They have been exposed to environmental factors, such as radiation and chemicals, for longer They have had more of a chance to damage their DNA
48
How does ionising radiation cause cancer?
Includes X-rays, alpha and beta radiation | Has a lot of energy so can penetrate body cells and break bonds in DNA molecules
49
How does UV radiation cause cancer?
Has enough energy to penetrate skin cells | Breaks bonds in DNA and can cause skin cancer
50
How can chemicals cause cancer?
Cancer causing chemicals are called carcinogens | Cigarette smoke, asbestos, some pesticides and diesel exhaust can cause cancer
51
How can viruses cause cancer?
HPV is the best known example | It carries the code for a protein that interferes with a tumour suppressor gene
52
What is the process by which gametes are formed called?
Meiosis
53
What is the diploid number in humans?
2n = 46
54
What is a cell with a homologous pair of chromosomes called?
Diploid
55
Why do gametes have to be haploid (n = 23)?
Because each individual develops from a zygote that divides by mitosis
56
What happens in the first stage of meiosis?
Two cells are formed | Each chromosome still has two chromatids
57
What happens in the second stage of meiosis?
The chromatids divide, making four haploid cells
58
What can go wrong in meiosis?
A gamete can end up with one less or one more chromosome
59
What problems will arise if one of these gametes fuses with a normal gamete?
The zygote will have one extra or one missing chromosome
60
What is this called?
Non-disjunction
61
What causes Down's syndrome?
When someone has 3 copies of chromosome 21 (trisomy 21)
62
How is trisomy 21 formed?
When a gamete with two copies of chromosome 21 fuses with a normal gamete, which has one copy, to get 3 copies
63
When does the risk of having a Down's syndrome increase?
As the woman gets older
64
What are some characteristics of a person with Down's syndrome?
``` Flatter head than normal Smaller ears Protruding ears Shorter than average Single crease along the palm ```
65
What do all Down's syndrome people suffer with?
Learning difficulties
66
Describe the personality and lifestyle of a Down's syndrome person
Very happy Very affectionate Some can enter employment and lead independent lives Some may need lifelong care
67
What is the average life expectancy for someone with Down's syndrome?
60 years

AS Human Biology (4 decks)

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