M2 - Chapter 6 - Cell Division Flashcards
what is the cell cycle
a sequence of ordered events that takes place in a cell, resulting in division happening and then the formation of 2 genetically identical daughter cells.
a cell spends most of its time in what stage
Interphase
What happens in interphase
- DNA is replicated and checked for errors.
- Protein synthesis (enzymes and hormones are replicated)
- The number of chloroplasts in plants also divides (it increases in size first and then it splits)
- Mitochondria will also grow and divide (again grows and then splits) This is because mitosis requires a lot of energy, obtained from mitochondria.
Stages in interphase
G1- Growth stage 1 - The protein content and the amount of cell organelles increases (by growing and then splitting), to hold everything together.
S- Synthesis stage - DNA is replicated here
G2- Growth stage 2 - Cells continues to increase in size. The energy stores are also increased (ATP, glucose, fats and oils). The duplicated DNA is checked for errors. If there is damage, it will fix it by using free nucleotides.
Mitotic phase
The actual cell division takes place here.
4 stages here
After this is cytokinesis, which is the actual splitting of the cells into 2 daughter cells.
What is G0
This is called the “resting stage”, where there is no growth that can be caused. The cell will leave the cycle, but this can be temporary or permanent.
- Differentiation (if the cell becomes specialised to carry out a specific task and can no longer divide at all)
- DNA of a cell may be damaged so it can’t differentiate. It can enter a period of Permanent cell arrest.
- As you age, the number of ineffective (called senescent) cells increases, which are related to many age-related diseases.
How does exercise affect the number of senescent cells
As you exercise more, you force your cells to keep being used up and hence they duplicate more. This way there are more cells, and more ATP created, leading to more movement.
What is a checkpoint
Control mechanisms of the cell cycle. It monitors and verifies whether the processes at each phase have been completed accurately, to allow the next phase to occur.
3 checkpoints
- Spindle assembly
- G1
- G2
Explain G1 checkpoint
It looks for: - cell size - nutrients - growth factors - any DNA damage If these criteria aren't met, then it goes to the resting state. It does this before it goes to the S stage.
G2 checkpoint
It looks for: - Cell size - DNA replication - DNA damage Happens before going into the mitosis
Spindle assembly checkpoint
It is in the mitosis stage, just before it finishes.
it is also called the metaphase and it ensures that all the chromosomes are attached to spindle fibres. If it isn’t mitosis can’t happen.
Cell- cycle regulation and cancer
The passing of a cell cycle checkpoint is done by kinase, which is an enzyme that catalyses the addition of a phosphate group to a protein (called phosphorylation). When kinases binds to a variety of checkpoint proteins called cyclins. It creates a “Cyclin- Dependent kinase complex”. By having them, it ensures that a cell progresses through phases at the correct times.
Define cancer
caused by uncontrolled division of cells
Define tumour
an abnormal mass of cells.
They are caused by the damage or spontaneous mutation of genes.
Define benign
If the tumour stops growing and don’t travel.
Define malignant
If the tumour can move and continues to grow.
CDK can also be used as…
A target for chemical inhibitors to treat cancer. It would reduce CKDs, and reduce cell division, hence cancer cell formation.
what is mitosis
When a cell divides to create 2 daughter cells that are identical to the parental cell. Generally good for growth, replacement, repair or asexual reproduction.
Before and after of replication of chromosomes.
Before: there’s a single chromatid per chromosomes.
After: 2 chromatids per chromosomes.
4 stages of mitosis
Prophase
Metaphase
Anaphase
Telophase.
Prophase
Nuclear membrane disintegrates and breaks down.
The chromatin fibres condense into individual chromosomes as they begin to coil.
The nucleolus disappears.
Centrioles will move to the poles.
The centrioles form protein microtubules.
Metaphase
In this stage, the chromosomes move to the equator and the middle, creating a mitotic spindle.
The spindle fibres attach to the chromosomes at the centromere.
Anaphase
In this stage, the chromosomes are actually pulled apart to the opposite ends. This is because the centromere actually divides as well. Motor proteins can help sometimes too.
Note for anaphase
This process needs a lot of ATP, so mitochondria gathers around the spindle fibre.
Telophase
The chromatids reach the ends of the poles and are now called chromosomes.
The nuclear membrane forms again.
Chromosomes begin to uncoil.
Nucleolus is also formed again
Cytokinesis
It begins during the telophase.
The cleavage furrow pinches the cell together. An indentation of the plasma membrane, as it folds inwards by the cytoskeleton, until it is close enough to fuse together.
Plant cells and cytoskeleton
They have cell walls that can’t allow a cleavage furrow to be formed. Instead vesicles from the Golgi form along the equator and they fuse to create a “cell plate”, dividing into 2 cells.
Explain meiosis
The nucleus divides twice to produce 4 daughter cells (called gametes (sex cells)).
How many chromosomes does a haploid gamete have
- it only has 1 set of chromosome.
What is meiosis often called
A reduction division
Explain homologous chromosomes
You have 46 chromosomes in your cells, of which, you get 23 from your mum, and another 23 from your dad. Each 23 chromosomes is called a set of chromosomes. This means that chromosome 1 from your mum and chromosome 1 from your dad will not be the same, however it will code for the same type of genes. They will have different or maybe the same allele, depending on what characteristic it codes for and if your parents have that same characteristic.
What do homologous chromosomes have in common
same length
same size
centromeres in the same position
same genes in the same position
stages in meiosis
meiosis 1: first division
Each cell contains only 1 full set of genes rather than 2 (haploid)
meiosis 2: second division
The chromosomes in each daughter cell are separated, forming 2 more cells, resulting in 4 haploid cells in total.
Interphase in meiosis 1
The chromosomes replicate, they create 2 sister chromatids that are joined together by a centromere
Prophase in meiosis 1
Nuclear envelope disintegrates
Chromosomes condense and they coil
Nucleolus disappears
The homologous chromosomes join together, to create a bivalent (a homologous chromosome pair).
As the chromosomes move, they often get tangled together, which creates crossing over. When this happens, the alleles that get crossed over can swap. This causes genetic variation.
Metaphase in meiosis 1
The chromosomes line up along the metaphase plate.
The orientation of each bivalent is completely independent. The father chromosomes can face the north or the south pole, but it results in genetic variation. This is due to the independent assortment of homologous chromosomes.
Anaphase in meiosis 1
The centrioles pull the chromosomes to either side of the pole. The chromatids stay together, but split at the chiasmata (which is the allele that has been swapped, also the breaking point).
When this exchange of genes happens, it creates a recombinant chromatid. Again, resulting in genetic variation.
Telophase in meiosis 1
The chromosomes uncoil.
They undergo cytokinesis.
Then cytokinesis happens.
overall meiosis 2
It is the same as mitosis.
There is no interphase stage.
Prophase in meiosis 2
chromatids condense
Nuclear envelope breaks
Metaphase in meiosis 2
centrioles line them up along the middle.
another independent assortment of sister chromatids here can result in genetic variation.
Are the alleles (that are swapped) on the same side or different side?
Anaphase in meiosis 2
Splitting of centromere.
Separates sister chromatids.
Telophase in meiosis 2
Chromosomes uncoil.
Nuclear envelope reforms and the nucleolus becomes visible again.
Same thing happens to the other cell that was made in meiosis 1, so it results in 4 haploid cells being made.
Another cause of genetic variation here is whether or not the the allele swapped is in the same cell, or different cells?
what does specialised mean
They have adapted to carry out a specific function
how can you summarise the organisation of a multi cellular organism
specialised cell -> tissues -> organs -.>organ systems
-> whole organism
Examples of animal specialised cells
Erythrocytes
Neutrophils
Sperm cells
Erythrocytes
Red blood cells
- Flattened biconcave shape to increase SA:V ratio
- No nucleus, to carry more oxygen
- Flexible to fit through narrow capillaries.
Neutrophils
A type of white blood cell
they have a multi-loaded nucleus ( to make it easier to squeeze through at the site of infections)
- granular cytoplasm ( contains many lysosomes to attack pathogens)
Sperm cells
Flagellum to move
Mitochondria (energy)
Acrosomes (Digestive enzymes to digest the layers of the sperm cell)
Specialised plant cells
Palisade cells
Root hair cells
Guard cell
palisade cell
large amount of chloroplasts cells are rectangular (can be packed closely) thin walls (increase rate of diffusion) large vacuole (maintain turgor pressure) chloroplasts can move within cytoplasm
root hair cells
increase SA of the cell
maximises the uptake of water and minerals
vacuole contains cell sap (low water potential)
guard cells
change shape
thicker walls on the inside so it doesn’t change shape symmetrically.
what is a tissue
a collection of differentiated cells that have a specialised function
Categories of tissues
- Nervous tissue transmission of electrical impulse - Epithelial tissue adapted to cover body surface both internal and external - Muscle tissue contract - Connective tissue either to hold other tissues together or as a transport medium.
Specialised animal cells
squamous epithelium
ciliated epithelium
cartilage
muscle
squamous epithelium
made up of specialised squamous epithelial cells
very thin
present when rapid diffusion is needed
forms the lining of the lungs to allow rapid diffusion
ciliated epithelium
made up of ciliated epithelial cells
they have cilia to move mucus
Goblet cells release mucus to trap bacteria.
Cartilage
Found in the outer ear, nose and in between bones
It contains fibres of protein elastin and collagen
Composed of chondrocyte cells embedded in an extracellular matrix
prevents bones from rubbing against each other.
muscle cells
They contain myofibrils, that contain proteins.
Types of tissues in plants
epidermis (adapted to cover plant tissues) Vascular tissue (adapted for transport of water and minerals)
Epidermis
Allow gases to move in and out
Xylem
Transport of water and minerals
Composed of vessel elements (elongated dead cells)
walls of xylem are strengthened with a waterproof material called lignin for structural support.
Phloem
Transport of organic nutrients, mainly sucrose
Composed of columns of sieve tube cells separated by sieve plates.
what is an organ
A collection of tissues that are adapted to perform a particular function in an organism.
Examples of an organ
digestive system
cardiovascular system
gaseous exchange system
What is a stem cell
Undifferentiated cells that aren’t adapted to a function and can become specialised
Why do stem cells have to be controlled
If they divide too quickly, then a tumour might form. If not enough, then cells won’t be replaced quickly enough
What is stem cell potency
A stem cell’s ability to differentiate into different cell types is called its potency
Totipotent
They can differentiate into any cell type.
They can form a whole new organism.
Pluripotent
These stem cells can form all tissue types but they can’t form whole organisms.
They are present in early embryos and are the origin of different tissues.
Multipotent
They can only form a range of cells within a certain type of tissue
Differentiation
All multicellular organisms have evolved from unicellular. This is because certain groups of cells have different function and they work together as 1 unit. This means they can use resources better than single cells.
Replacement of red blood cells
Because they don’t have many organelles or a nucleus, it means that they have a small life span of 120 days. Colonies of stem cells in the bone marrow have to make 3 billion red blood cells per kg of body mass everyday.
Replacement of white blood cells
They only live for 6 hours. Colonies of stem cells have to make 1.6 billion white blood cells per kg per hour.
Embryonic stem cells
Are totipotent
After 7 days, a blastocyst (a mass of cells) has formed and the cells remain in the pluripotent.
Tissue adult stem cells
Multipotent
From birth to life
Found in specific areas (like bone marrow)
No evidence if they can be artificially triggered to become pluripotent.
Where else can stem cells be found
In the umbilical cord. Can be stored just in case
Sources of stem cells in plants
Present in the meristematic tissue
Found wherever there in growth (roots or shoots)
Also found in between the phloem and xylem tissues, called vascular cambium.
Pluripotent nature
Uses of stem cells
Treat heart disease
Type 1 diabetes
Parkinson’s disease (death of dopamine-producing cells in the brain. So far only drugs can delay it.)
Alzheimer’s disease (brain cells destroyed due to abnormal protein)
Macular degeneration (blindness in the elderly)
Birth defects
Spinal injuries
Where have stem cells have already been used
Treatment of burns (stem cells grown on biodegradable mesh for new skin)
Drug Trials (can be tested on culture of stem cells)
Developmental biology- studying them
Ethics about stem cells
Law in UK changes so that embryos can be created in the labs.
Removal of stem cells from embryos usually kills embryos. However, research in being done to undo this.
Religious: where does life begin? should the embryos have rights?
Using adult stem cells can be okay but are more likely to acquire mutations.
Discuss the ways in which genetic variation is produced, including the role of nuclear division
In prophase I, crossing over occurs. Here, alleles are swapped between the 2 chromatids.
In metaphase I, an independent assortment of homologous chromosomes can also occur.
In metaphase II, an independent assortment of sister chromatids occurs.
Also, the alleles swapped will be different because they have come from 2 different people.
The fusion of gametes is random and since they are all different, it can create a large number of chromosomes.
Explain why meiosis needs to have twice as many stages as mitosis.
So that the number of chromosomes halve as gametes are meant to be haploids. It’s also so that the homologous pairs and the sister chromatids can separate because the DNA Replicated at the beginning.
Discuss how cells are organised into tissues using xylem and phloem as examples
Xylem consists of vessels and it has lignified walls, that are strong. It allows the movement of water and mineral, called the transpiration stream.
Phloem is made up of sieve tubes elements and companion cells. It contains no nucleus in the sieve tube elements and is for movement of sucrose (called translocation).
Specialisation of xylem
waterproof walls lignified walls no end walls it has bordered pits (acts as a safety valve) no organelles no cell contents
Specialisation of phloem
Sieve plates (in sieve tube elements)
No nucleus in sieve tube
Little cytoplasm in sieve tube
Many mitochondria in companion cells
Definition of a tissue
A group of specialised cells that work together to perform a function
Definition of an organ
A group of tissues working together to perform a specific function
Definition of organ system
A group of organs working together as a biological system to perform a specific function
Give one way in which gamete cells can increase variation?
Each gamete is different
The fusion of gametes is random
Each gamete contains DNA of 2 different people.
Why are the root tips placed in HCl?
The acid allows the stain to diffuse into the cells. It hydralyses the middle lamella.
Why are the root tips stained?
It binds to chromatin DNA, staining it a deep blue colour, which increases contrast and allows the cells to be seen.
Why are the root tips squashed?
To produce a layer that is only 1 cell thick. This is so that it doesn’t obscure the view of the chromosomes. They should be squashed very gently, though. This way, the tips aren’t damaged, or a coverslip.
How could the experiment could be changed to improve how well the chromosomes are seen?
Increase the time spend with HCl, increase temperature, etc.
