Chapter 8 - Cell Division Flashcards
What is the name of the process by which cells divide to make exact copies of themselves?
Mitosis
How is DNA organised in eukaryotic cells?
Into chromosomes
How many chromosomes do human cells have?
46
Why can’t you see chromosomes when a cell isn’t dividing?
The DNA is ‘unwound’ and spread out in the nucleus
What phase is a cell in if it isn’t dividing?
Interphase
What is chromatin?
DNA molecule wrapped around histones (proteins)
When does DNA replicate?
In interphase
What happens to chromatin when a cell starts to divide?
It coils up and folds to form chromosomes
What does a chromosome look like in prophase?
It has two sister chromatids, held together by a centromere
Why are there two chromatids?
The DNA replicated in interphase
What does the cell do in interphase?
Protein synthesis
Cell organelle replication
Respiration
What is interphase divided into?
G1, S and G2
What happens in growth phase 1 (G1)?
Cell organelle synthesis
Biochemicals produced
What happens in synthesis (S) phase?
DNA is replicated
What happens in growth phase 2 (G2)?
Energy stores are increased
What are the four phase of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens in prophase?
Chromosomes shorten and thicken
Spindle fibres form
Nuclear envelope disintegrates
What happens in metaphase?
Chromosomes are arranged on the equator
What happens in anaphase?
Chromosomes migrate to opposite poles
What happens in telophase?
Spindle fibres disintegrate
Nuclear envelope develops
What is mitosis important for?
Growth
Repair
Asexual reproduction
Explain the importance of mitosis in growth
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
Explain the importance of mitosis in repair
If cells die or are damaged, they need to be replaced by cells with exact same genetic information as them
Explain the importance of mitosis in
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
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
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
Explain what happens in anaphase in detail
Microtubules attached to the centromeres contract
Daughter chromosomes are pulled to the opposite poles
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
What is a tumour?
A mass of cells that have divided too many times
What types of tumour are there?
Benign and malignant
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
Describe malignant tumours
Grow rapidly
Invade surrounding tissues
Cells can break off from the main tumour
Life-threatening unless treated early
What are proto-oncogenes?
Genes that stop cells dividing by mitosis too often
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)
How else can proto-oncogenes work?
They produce the growth factor needed to stimulate cell division
When do proto-oncogenes become oncogenes?
When the base sequence changes; a mutation occurs
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
How else can oncogenes cause uncontrolled cell division?
They can produce uncontrolled amount of growth factor
What are tumour suppressor genes?
Genes that code for proteins that stop cells dividing
Also, they cause cells with damaged DNA to die
What would happen if a tumour suppressor gene mutated?
The cell might carry on dividing uncontrollably, passing on damaged DNA
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
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
What is the name for the spreading of tumour cells?
Metastatis
What are secondary tumours also known as?
A metastatis
What are the causes of cancer?
Genetic factors Age Ionising radiation UV radiation Chemicals Viruses
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
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
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
How does UV radiation cause cancer?
Has enough energy to penetrate skin cells
Breaks bonds in DNA and can cause skin cancer
How can chemicals cause cancer?
Cancer causing chemicals are called carcinogens
Cigarette smoke, asbestos, some pesticides and diesel exhaust can cause cancer
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
What is the process by which gametes are formed called?
Meiosis
What is the diploid number in humans?
2n = 46
What is a cell with a homologous pair of chromosomes called?
Diploid
Why do gametes have to be haploid (n = 23)?
Because each individual develops from a zygote that divides by mitosis
What happens in the first stage of meiosis?
Two cells are formed
Each chromosome still has two chromatids
What happens in the second stage of meiosis?
The chromatids divide, making four haploid cells
What can go wrong in meiosis?
A gamete can end up with one less or one more chromosome
What problems will arise if one of these gametes fuses with a normal gamete?
The zygote will have one extra or one missing chromosome
What is this called?
Non-disjunction
What causes Down’s syndrome?
When someone has 3 copies of chromosome 21 (trisomy 21)
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
When does the risk of having a Down’s syndrome increase?
As the woman gets older
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
What do all Down’s syndrome people suffer with?
Learning difficulties
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
What is the average life expectancy for someone with Down’s syndrome?
60 years
