3.2.2 All Cells Arise From Other Cells Flashcards
How’s dna passed onto the next generation
Through gametes
Who do dividing cells pass on their genetic info to
Produced daughter cells
What is dna made up of
Nucleotides containing deoxyribose sugar, organic base and a phosphate group
What forms between bases in dna structure
Hydrogen bonds
2 gametes
Egg + sperm cells
What’s the opposite of a gamete
Somatic (body) cell
What cells are gametes known as
How many chromosomes do they have
Haploid cells
23
What cells are somatic (body) cells known as
How many chromosomes do they have
Diploid
46
In the nucleus, what’s genetic information stored as
Chromosomes
How are chromosomes arranged in humans
In pairs (homologous chromosomes)
On homologous chromosomes what’s the locus
Position of gene within the chromosome
Pairs have same locus’
When are sister chromatids formed
During replication of dna which must occur before cell division 5
What’s a centromere
Circle in centre of a chromatid
What do sister chromatids make up
Chromosomes
What’s mitosis used for
Growth and repair
What does meiosis produce
Gametes with 1/2 required genetic information
What are the chromosomes in the nucleus surrounded by
Free nucleotides used to build new dna molecules
What 2 enzymes are used to build new dna molecules
DNA helicase
DNA polymerase
What does dna helicase do and so cause
Breaks hydrogen bonds that hold bases together
Causes dna to unwind, exposing 2 single strands
What does DNA polymerase use as a template
The exposes single strand from dna helicase
What does DNA polymerase do
What are the new strands like and why
Assembles free nucleotides into a new strand alongside the template
New strands are complementary due to the base pairing rule
What’s dna replication
Unwinding + synthesis of new strands continuing along the entire dna molecule
Why is dna replication known as semi-conservative replication (2)
- Each dna molecule contains 50% original dna
2. Both new molecules are identical to each other + original
What’s the first part of the cell cycle which must occur before a cell divides
What’s this stage known as
DNA replication
Interphase
How many parts is interphase divided into (all before mitosis)
3
What are the 3 stages of interphase
G1 phase
S phase
G2 phas3
What happens in G1 of interphase (2)
The cell grows in size (gets 50% bigger)
New nucleotides + histones (proteins) are made ready for dna replication
What happens in s phase of interphase (3)
DNA is replicated (with dna helicase and DNA polymerase) synthesising new dna
Doubles chromatin in nucleus
Cell continues to grow
What’s chromatin like
Tangles (spaghetti) dna + histones
What are histones
What are they used to do
What charge are they
Circular proteins
Used to coil dna
Are positively charged (+)
What do histones bind to and what happens
how is this useful
Bind to negatively (-) charged dna which wraps round them
This condenses dna so it can fit in the nucleus
What’s synthesised in G2 of interphase
What forms
Tubulins (specialised proteins) are synthesised
Form spindle fibres
What do spindle fibres do that makes them needed for mitosis
They pull apart chromosomes
What’s the cell like in G2 of interphase
50% bigger than it should be
How long does the cell cycle roughly take in humans
24 hours
When does mitosis occur
After the cell growth + dna replication (preparation)
What does mitosis involve
Involves division of nucleus and then the cell itself. Producing 2 daughter cells
How many stages of mitosis are there
What are they
4 stages
Prophase
Metaphase
Anaphase
Telophase
Anagram for cell cycle and mitosis
IPMAT
I Play Monopoly At Tea
What happens in 1. Prophase (3)
Chromosomes coil
Chromatids become vision,e
Nuclear envelope begins to break down
What’s present prior to prophase
Chromatin
Why does the nuclear envelope begin to break down in prophase
So chromosomes can be separated into 2 new cells
What are centrioles
Poles of a cell
Where do spindle fibres (Tubulin proteins) come from
Centrioles (poles)
What’s all the spindle fibres known as
Spindle apparatus
What happens during metaphase (3)
Spindle fibres are formed (from tubulin)
Centromeres attach the chromatids to the spindle
Chromatids are arranged in the centre of the cell
What’s the centre of the cell called
Equator
Where do chromosomes line up in the cell
What is needed for this to happen
Equator
Spindle fibres
What happens in anaphase
Spindle fibres shorten + pull sister chromatids to opposite poles Centromeres divide (into 2)
What shape are sister chromatids as they get pulled to opposite poles
V shaped
In what situation might chromatids remain at the equator during anaphase
If chemicals are added to destroy the spindle
What happens during telophase (4)
2 sets of chromosomes gather at opposite poles
Spindle fibres break down
New nuclear envelope forms
Chromosomes uncoil to form chromatin (spaghetti)
What’s the process when cytoplasm divides producing 2 new daughter cells
Cytokinesis
What are the 2 new daughter cells like to each other and the original
Genetically identical
3 types of cells where mitosis occurs constantly
Hair
Small intestine
Skin
What has to be tightly controlled to have a healthy organism
Cell cycle
When do liver cells only divide
When it’s necessary
What prevents cells from dividing too rapidly by mitosis
Control mechanisms
3 control mechanisms
Need nutrients to divide
Need growth factor (protein) - triggers mitosis
Anaphase only starts if all chromosomes attach to spindle
Why are naturally occurring protein structures in dividing cells
To regulate mitosis and make sure it’s safe
What do checkpoints check
That all crucial processes have been carried out. If not, the cell becomes a non-dividing cell
What’s G1, G2 and Metaphase controlled by
Stop + go signals
What can lead to uncontrolled division
A mutation
What 2 things control mitosis
2 genes
What are the 2 types of tumours
Benign - safe, stays in 1 site
Malignant - dangerous, can spread
What cells don’t adhere to control mechanisms
Cancer cells
When can cancer cells be almost ‘immortal’
If given a continual supply of nutrients
What can tumours be caused by
Mitosis at a checkpoint (division not stopping)
What’s transformation
Turning a normal cell to a cancer cell (due to dna mutation impacting checkpoints )
What are cancer cells normally destroyed by
The immune system
What can cancer cells be affected by
E.g
Choice of lifestyle
E.g UV light, alcohol, cigarettes, genetic factors
What immune systems can make cancer worse
E.g
Weak immune systems
E.g diabetes
5 common organs where tumours can occur
Lungs Prostrate gland Breast Ovaries Large intestine Stomach Oesophagus Pancreas
2 examples of cancer treatment
What do they both do
Chemotherapy
Radiotherapy
Both block part of the cell cycle to kill cells
What’s chemotherapy in the form of
What does it target
Drugs put into bloodstream
Targets fast dividing cells but also healthy cells
What 2 things does chemotherapy prevent
Prevents dna replication (interphase)
Prevents spindle fibre forming (metaphase) - stops tubulin proteins
What’s radiotherapy
More targeted radiation
What does radiotherapy also disrupt
But what’s most affected
Also disrupts the cycles of healthy cells
Rapidly dividing cells are most affected
What can many mutations in cells dna make the cell over time
Malignant
What increases risk of mutations
E.g
Carcinogens
E.g UV light exposure, cigarette chemicals
What’s a virus
Tiny particles of nucleus acid (dna/rna) enclosed within a protein coat (capsid)
What type of organism are viruses
Why
Acellular organisms
Aren’t made from cells
What’s the capsid of a virus formed from
Formed from protein
Made from individual units called capsomeres
What on the capsid attaches to cell surface proteins of a host cell
Attatchment proteins
When a ci4us is attached to a host cell what does it do
It penetrates the cell and hijacks the machinery forcing the cell to produce viral rna/dna and protein to build new virus copies
How does the virus eventually destroy the host cell
When is eventually bursts out of the host cell, destroying it in the process
Are bacterial cells or viruses smaller
Viruses
What do some viruses have that’s additional which the attatchment proteins are on
E.g
Some have a lipid envelope
E.g HIV
When can viruses only show they’re living (reproduce)
If they’re inside a host cell
What are the 2 ways in which new virus copies can be released
Budding
Bursting
What happens during budding of viruses
Virus is released in a vesicle formed from part of the cells membrane
How does a virus grow if it contains RNA
Virus enters host cell + capsid is removed
The rna goes to the ribosomes of the host cell
Ribosomes produce enzymes needed to make viral proteins
How does a virus grow if it contains DNA
Virus enters host cell + capsid is removed
The DNA provides the code to produce viral RNA
The RNA goes to the ribosomes of the host cell
Ribosomes produce enzymes needed to make viral proteins
What type of reproduction is bacterial replication
Asexual reproduction
How long does bacterial replication take
About 20 minutes
What do prokaryotic cells divide by
Binary fission
5 parts of binary fission process
- Circular naked dna replicates + both copies of dna attatch to the cell membrane at opposite ends of the cell
- Plasmids are replicated too
- Cell grows in size
- Cell membrane grows between the 2 dna molecules. It pinches inwards and cytoplasm begins to divide
- A new cell wall forms between the 2 copies of dna. Original prokaryotic cell becomes 2 identical daughter cells
3 conditions prokaryotes need for binary fission
Warm, moist, oxygen rich
