Module 2 Section 6: Cell Division and Cellular Organisation Flashcards
When does the cell cycle start and end
Starts when a cell has been produced by cells division
Ends with the cell dividing to produce two identical cells
What does the cell cycle consist of
Cell cycle consists of:
A period of cell growth and DNA replication - interphase
A period of cell division - M phase
M phase involves mitosis ( nuclear division ) and cytokinesis ( cytoplasmic division )
What is the interphase divided into
Interphase ( cell growth ) is subdivided into three separate growth stages
These are called G1, S and G2
How is the cell cycle regulated
Regulated by checkpoints
Checkpoints occur at key points during cycle to make sure its okay for the process to continue
What happens in G1 phase
Growth Phase 1:
Cell grows in size
Proteins synthesised
Organelles replicate ( mitochondria, ribosomes etc )
What happens in the S phase
Synthesis phase:
Replication of each chromosome in nucleus
Now called sister chromatids ( joined at centromere )
What happens in the G2 phase
Growth 2 phase:
Cell grows in size
Duplicated DNA checked for errors
Energy stores ( ATP ) are increased
What does the G1 checkpoint check for
Checks:
Cell is the correct size
Nutrients/ chemicals are present
Growth factors present
Any damage to DNA
Before entering S phase
What does G2 checkpoint check for
Checks:
Cell is correct size
DNA has been replicated without damage
If this is correct, cell can enter mitosis
What does the spindle assembly checkpoint ( metaphase checkpoint ) check for
Checks for:
Chromosome attachment to the spindle
Full stages of cell cycle
Gap phase 1
G1 checkpoint
Synthesis
Gap phase 2
G2 checkpoint
M phase
Spindle assembly checkpoint ( metaphase checkpoint )
What is the cell cycle needed for
Growth of tissue/ organism ( not of cells )
Replacement of worn out/ damaged cells
Repair of body tissues ( e.g. bone, muscle )
Asexual reproduction/ cloning
What are the stages that mitosis is separated into
Mitosis is one continuous process
Can be described as a series of division stages:
Prophase
Metaphase
Anaphase
Telophase
What happens during the interphase
Cell carries out normal functions
Prepares to divide
DNA unravelled and replicated, to double amount of chromosomes
Organelles replicated to make spares
ATP content is increased
What happens during prophase
Chromosomes condense, getting shorter and fatter
Centrioles move towards opposite ends of the cell
Form spindle fibres across cell
Nuclear envelope breaks down and chromosomes lie free in the cytoplasm
What happens during the metaphase
Chromosomes ( as two sister chromatids ) line up along the middle of cell
Their centromere is attached to the spindle fibres
Metaphase checkpoint occurs here
What happens during the anaphase
Centromeres divide
This separates each pair of sister chromatids
Spindles contract, pulling chromatids to opposite ends of the cell, centromere first
What happens during the telophase
Chromatids reach opposite poles on spindle fibres
They uncoil and become long and thin
Called chromosomes again
A nuclear envelope forms around each group of chromosomes so there are two nuclei
What happens in cytokinesis
Cytoplasm divides
In animal cells, a cleavage furrow forms to divide the cell membrane
There are now two daughter cells that are genetically identical to original cell and to eachother
Cytokinesis usually begins in anaphase and ends in telophase
Separate process to mitosis
What are multicellular organisms made of
Made up of different cell types that are specialised for their functions
E.g. liver cells, muscle cells, white blood cells
Where do specialised cells come from
These all originated came from stem cells
What are stem cells
Stem cells are unspecialised cells
They can develop into different types of cell
All multicellular organisms have some form of stem cells
Where are stem cells found in humans
Stem cells usually found in early embryos and in a few places in adults
What can stem cells in early embryos do
They can develop into any type of human cell
They are pluripotent
What can adult stem cells do
Stem cells in adults can only develop into a limited range of cells
They can also divide to produce more undifferentiated stem cells, so they can renew themselves
They are multi potent
How do stem cells become specialised cells
Stem cells divide to become new cells, which then become specialised
This process where cells become specialised for their job is called differentiation
What are stem cells used for in animals
Used to replaced damaged cells
E.g. to make new skin or blood cells
What are stem cells used for in plants
Plants are always growing
So stem cells are needed to make new shoots and roots throughout their lives
Stem cells in plants differentiate into various plant tissues including xylem and phloem
How do cells in bone marrow differentiate into blood cells
Bone are living organs, containing nerves and blood vessels
The main bones of the body have marrow in the centres
Here, adult stem cells divide and differentiate to replace worn out blood cells
These can be erythrocytes (red blood cells) and neutrophils (white blood cells that help fight infection)
How do cells in the meristem differentiate into xylem and phloem
In plants, stem cells are found in the meristems (parts of the plant where growth can taken place)
In the root and stem, stem cells of the vascular cambium divide and differentiate to become xylem vessels and phloem sieve tubes
Meristems can be used for repair of damaged tissue
What can scientists use stem cells for
Stem cells can develop into different specialised cell types, so scientists think they can be used to replace tissues in a range of diseases e.g. Alzheimer’s and Parkinson’s
How cans stem cells be used to treat Alzheimer’s disease
With Alzheimer’s, nerve cells in the brain die in increasing numbers
This results in severe memory loss
Researchers hope stem cells can be used to regrow healthy nerve cells in people with Alzheimer’s
How can stem cells be used to treat Parkinson’s
Parkinson’s disease causes tremors that patients can’t control
The disease causes a loss of a particular type of nerve cell in the brain
These cells release dopamine which is used to control movement
Transplanted stem cells may help regenerate the dopamine-producing cells
Structure and function of neutrophils
Neutrophils (a type of white blood cell) defend the body against disease
Their flexible shape allows them to engulf foreign particles or pathogens
The many lysosomes in their cytoplasm contain digestive enzymes to break down the engulfed particles
Lobed nucleus
Structure and function of erythrocytes
Erythrocytes (red blood cells) carry oxygen in the blood
The biconcave disc shape provides a large surface area for gas exchange
They have no nucleus so there’s more room for haemoglobin, the protein that carries oxygen
Structure and function of epithelial cells
Epithelial cells cover the surface of organs
The cells are joined by interlinking cell membranes and a membrane as their base
Ciliated epithelia (e.g. in the airways) have cilia that beat to move particles away.
Structure and function of sperm cells
Sperm cells (male sex cells) have a flagellum (tail) so they can swim to the egg (female sex cell)
They also have lots of mitochondria to provide the energy to swim
The acrosome contains digestive enzymes to enable the sperm to penetrate the surface of the egg
Structure and function of palisade mesophyll cells
Palisade mesophyll cells in leaves do most of the photosynthesis
They contain many chloroplasts, so they can absorb a lot of sunlight
The walls are thin, so carbon dioxide can easily diffuse into the cell
Structure and function of root hair cells
Root hair cells absorb water and mineral ions from the soil
They have a larger surface area for absorption and a thin permeable cell wall, for entry of water and ions
The cytoplasm contains extra mitochondria to provide the energy needed for active transport
Structure and function of guard cells
Guard cells are found in pairs, with a gap between them to form a stoma
This is one of the tiny pores in the surface of the leaf used for gas exchange
In the light, guard cells take up water and become turgid
Their thin outer walls and thickened inner walls force them to bend outwards, opening the stomata
This allows the leaf to exchange gases for photosynthesis
Structure and function of squamous epithelium (tissue)
This is a single layer of flat cells lining a surface
It’s found in many places, including the alveoli in the lungs
Structure and function of squamous epithelia (cells)
Squamous epithelia (e.g. in the lungs) are thin to allow efficient diffusion of gases
Structure and function of ciliated epithelium
Ciliated epithelium is a layer of cells covered in cilia
It’s found on surfaces where things needs to be moved - in the trachea for instance, where the cilia waft mucus along
Structure and function of muscle tissue
Muscle tissue is made up of bundles of elongated cells called muscle fibres
There are three different types of of muscle tissue:
Smooth (e.g. found in be lining of the stomach wall)
Cardiac (found in the heart)
Skeletal (which you use to move)
They’re all slightly different in structure
Structure and function of cartilage
Cartilage is a type of connective tissue found in the joints
It also shapes and supports the ears, nose and windpipe
It’s formed when cells called chondroblasts secrete an extracellular matrix (a jelly-like substance containing protein fibres), which they become trapped inside
Structure and function of xylem tissue
Xylem tissue is a plant tissue with two jobs - it transports water around the plant, and it supports the plant
It contains hollow xylem vessel cells, which are dead, and living parenchyma
Structure and function of phloem tissue
Phloem tissue transports sugars around the plant
It’s arranged in tubes and is made up of sieve cells, companion cells, and some ordinary plant cells
Each sieve cell has end walls with holes in them, so that sap can move easily through them
These end walls are called sieve plates
What is an organ made up of
Organ is a group of tissues that work together to perform a particular function
Example of an organ made up of different tissues in animals
The lungs - they contain squamous epithelial tissue (in the alveoli) and ciliated epithelial tissue (in the bronchi, etc)
They also have elastic connective tissue and vascular tissue (in the blood vessels)
Example of an organ made up of different tissues in plants
Leaves - they contain palisade tissue for photosynthesis, as well as epidermis tissue (to prevent water loss from the leaf), and xylem and phloem tissues in the veins
What is an organ system made up of
Organs work together to form organ systems - each system has a particular function
What is the G0 phase
When the cell leaves the cell cycle, either temporarily or permanently
This can be caused by:
Differentiation
DNA damages
Senescent cells (cell stops dividing but carries on working as an organism ages)
How do plant cells undergo cytokinesis
Plant cells have cell walls so a cleavage furrow cannot form
Vesicles from the Golgi apparatus assemble in the same place as where the metaphase plate was formed
Vesicles fuse with each other and the cell surface membrane, dividing the cell into two
New sections of cell wall then form along new sections of membrane
What happens in sexual reproduction
Two gametes (egg and sperm) join together at fertilisation to form a zygote
The zygote then divides and develops into a new organism
What is meiosis
Type of cell division that happens in the reproductive organs to produce gametes
What type of division does meiosis involve
Meiosis involves a reduction division
Cells that divide by meiosis have the full number of chromosomes to start with, but the cells that are formed from meiosis have half the number
What are haploid cells
Cells with half the normal number of chromosomes are called haploid cells
Are the cells formed by meiosis genetically identical or different to eachother
Cells formed by meiosis are all genetically different because each new cell ends up with a different combination of chromosomes
How many divisions does meiosis have and why
Meiosis involves two divisions: meiosis 1 and meiosis 2
To separate homologous pairs and sister chromatids
The gametes made must have half the number of chromosomes so they can bind to form zygote with complete number at fertilisation
How are meiosis 1 and 2 split up into stages
Like mitosis both meiosis 1 and meiosis 2 are split up into prophase, metaphase, anaphase, telophase
How does the whole of meiosis begin
The whole of meiosis begins with interphase
During interphase, the DNA unravels and replicates to produce double armed chromosomes called sister chromatids
What happens in prophase 1
The chromosomes condense, getting shorter and fatter
The chromosomes arrange themselves into homologous pairs (called bivalents)
Crossing over occurs
Just like mitosis, centrioles start moving to opposite ends of the cells, forming spindle fibres
Nuclear envelope breaks down
What happens in metaphase 1
The homologous pairs line up across the centre of the cell (not individual chromosomes) and attach to the spindle fibres by their centromeres
Independent assortment occurs here
What happens in anaphase 1
Spindles contract
Homologous pairs are separated
One chromosome goes to each end of the cell
Individual chromatids stay joined together
What happens in telophase 1
A nuclear envelope forms around each group of chromosomes
Chromosomes uncoil
What happens in cytokinesis (meiosis 2)
Division of the cytoplasm
Two haploid daughter cells are produced
What are homologous chromosomes
Humans have 46 chromosomes, 23 pairs in total
In each pair of chromosomes 1 comes from the paternal side and 1 comes from the maternal side
This means there are two number 1 chromosomes (one from mum, one from dad) and two number 2s in each cell
The chromosomes that make up each pair are the same size and have the same genes, although they could have different versions of those genes (called alleles)
These pairs of chromosomes are called homologous pairs
What happens in meiosis 2
The two daughter cells undergo prophase 2, metaphase 2, anaphase 2, telophase 2 and cytokinesis
These are a lot like the stages in mitosis
What happens in anaphase 2
Centromeres divide
Chromatids of the individual chromosomes are pulled to either end of the cell
(Same as anaphase in mitosis)
Products at the end of meiosis 1 and at the end of meiosis 2
End of meiosis 1: two diploid daughter cells
End of meiosis 2: 4 haploid daughter cells
How does crossing over work
Chromatids cross over in prophase 1
During this phase, homologous pairs of chromosomes (bivalents) are held together at points called chiasmata
The chromatids twist around eachother and parts of the chromatids swap over
The chromatids still contain the same genes but now have a different combination of alleles
How does meiosis produce genetically different cells
Crossing over of chromatids
Independent assortment of chromosomes
How does the independent assortment of chromosomes cause genetic differences
Each homologous pair of chromosomes in your cells is made up of 1 paternal and 1 maternal chromosome
When the homologous pairs line up in metaphase 1 and separate in anaphase 1, it’s completely random which chromosome from each pair ends up in which daughter cell
So the 4 daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes
This shuffling of chromosomes leads to genetic variation in any potential offspring
What type of cell are gametes
They are haploid cells as they contain half the amount of chromosomes as a normal (diploid) cell
Prophase 2
Chromosomes (consisting of two chromatids) condense and become visible
Nuclear envelope breaks down
Metaphase 2
Different from metaphase 1
Individual chromosomes assemble on the metaphase plate (like in mitosis)
There is independent assortment and more genetic variation due to crossing over
Telophase 2
Chromatids assemble at the poles of the cell (like in mitosis)
Chromosomes uncoil and form chromatin again
Nuclear envelope reforms
Cytokinesis (meiosis 2)
Division of the cells forming four daughter cells in total
Cells are haploid due to reduction division
Genetically different from each other, and parent cell
This is due to crossing over and independent assortment
Microscope pictures for interphase
Cell cycle diagram
Microscope pictures for prophase
Microscope pictures for metaphase
Microscope pictures for anaphase
Microscope pictures for telophase
