2.6 Cell division Flashcards
What is the cell cycle?
Sequence of events that take place, resulting in the division of the cell
What are the two main phases in the cell cycle
Interphase and mitotic phase
What is interphase
Long periods of growth and normal workings
What happens during interphase?
DNA is replicated and checked for errors in the nucleus, Protein synthesis occurs in the cytoplasm, Mitochondria grow and divide, (chloroplasts grow and divide), Normal metabolic processes if cells occur
What are the three stages of interphase?
G1
S
G2
What occurs during G1 of interphase
Proteins from which organelles are synthesised and produced, organelles replicate, increasing cell size
What occurs during S of interphase?
DNA is replicated in the nucleus
What occurs in G2 of interphase
Cell increases in size, energy stores are increased and duplicated, DNA is checked for errors
What is the difference between mitosis and cytokinesis
Mitosis - nucleus divides
Cytokinesis - cytoplasm divides, two cells are produced
What is G0
During stage G1 Cell leaves the cycle, either temporarily or permanently
Why might a cell enter G0?
Differentiation - cell becomes specialised and is no longer able to divide (does not re-enter)
DNA of a cell may be damaged - No longer viable, normal cells can only divide a limited number of times, eventually becoming senescent (does not re-enter)
What are checkpoints in the cell cycle
Monitor and verify whether the processes have been accurately completed, before the cell can progress
Where is the G1 checkpoint? What do this check for? Where does an unsatisfactory cell go?
G1 checkpoint - end of G, before entry into S, checks for cell size, nutrients, growth factors, DNA damage
Cell travels to G0 (resting state)
Where is the G2 checkpoint? What do this check for? Where does an unsatisfactory cell go?
End of G2 phase, before mitotic phase, checks for cell size, DNA replication, DNA damage
If not cell goes to resting state
Where is the Spindle assembly (metaphase) checkpoint? What do this check for? Where does an unsatisfactory cell go?
During metaphase, all chromosomes should be attached to spindles, Mitosis cannot occur until this checkpoint is passed
What enzyme allows the passing of a cell cycle checkpoint? What does this enzyme do?
Kinases
Catalyse the addition of a phosphate group to a protein (cyclins), Forming a CDK (cyclin dependent kinase) changing the tertiary structure
What is cancer? What is a tumour
Uncontrolled division of cells, abnormal mass
What is the difference between benign and malignant tumours
Benign - Stop growing and do not travel to other locations
Malignant - Does not stop growing, can break off and spread to other areas
What can cause tumors?
Damage or mutation of genes that encode proteins needed to regulate cell cycle.
Overexpression of cyclin gene, disrupts cell cycle, leading to uncontrolled division
Why is mitosis important?
Growth, replacement and repair, asexual reproduction
What is a chromatid? What is a centromere
Chromatid - identical DNA molecules
Centromere - area that joins the chromatids
What are the four stages of mitosis?
PMAT
Prophase
Metaphase
Anaphase
Teleophase
What is Prophase? Draw a diagram
Chromosomes condense, Nucleolus disappears and the nuclear membrane begins to break down, Spindle structures at poles of cell formed, centrioles migrate to poles. Spindle fibres attach to centromere and begin to pull them to the centre of the cell
What is metaphase. Draw a diagram
Chromosomes are moved by spindle fibres, chromosomes line up in the middle of a cell, caused the metaphase plate
What is anaphase. Draw a diagram
Centromeres divide, chromatids are separated due to the shortening of spindle fibres
What is telophase. Draw a diagram
Chromatids have reached the poles, and are now called chromosomes, two new sets of chromosomes assemble, nuclear envelope reforms, chromosomes start to uncoil and the nucleolus is formed
What is cytokinesis
Actual division of cell into two separate cells
What is a cleavage furrow?
In animal cells, a cleavage furrow forms around the middle of the cell, cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to close enough to fuse
What happens in plant cells during cell division?
Cell wall prevent formation of a cleavage furrow, Vesicles from the Golgi apparatus assemble and fuse with one another, cell surface membrane divides in two, cell wall forms along cell membrane
Compare diploid cells and haploid cells
Diploid - two chromosomes of each type (one from each parent)
Haploid - One chromosome of each type (gamete)
What is a gamete? What is a Zygote
Gamete - Haploid sex cell (sperm or egg)
Zygote - fertilised egg, combination of two gametes
How are gametes formed? What division is this?
Formed by meiosis, reduction division
What are homologus chromosomes
matching sets of chromosomes, has the same genes at the same loci
What is the loci of genes
Position of genes on a chromosome
What is an allele
Different versions of the same gene. (eg different eye colours)
Compare Meiosis and mitosis
Mitosis - 2 identical daughter cells
1 division
PMAT
Meiosis - 4 genetically different daughter cells
2 divisions
PMAT PMAT
What is the stages in meiosis
Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II
What happens in Meiosis I
First division, each cell only contains one full set of genes, instead of two, cells are haploid
Prophase I, Metaphase I, Anaphase I, Telophase I
What happens in Meiosis II
Second division, forming 2 new cells, four haploid cells are produced
When does crossing over of chromosomes occur, What does this cause
Crossing over occurs in Prophase I, this causes genetic variations
What happens in Prophase I
Chromosomes condense, nuclear envelope disintegrates, nucleolus disappears.
Homologous chromosomes pair up, forming bivalents, chromosomes entangle, causing crossing over
What happens in Metaphase I
same as mitosis, but
Orientation of each pair of homologous pairs is random, maternal (female parent of parent) or parental (male, parent of parent) chromosomes can end up facing either pole, resulting in independent assortment
What happens in Anaphase I
Homologous chromosomes are pulled to poles, chromatids remain joined.
Sister chromatids become entangled, break of and re-join, (break is called chiasmata), if exchange occurs, this forms recombinant chromatids (alleles are exchanged). This leads to genetic variation
What happens in telophase I, and after telophase I
Chromosomes assemble at poles, nuclear membrane reforms, chromosomes uncoil.
After - cytokinesis - reduction in chromosome number, from diploid (two chromatids) to haploid (One chromatid)
What happens in Prophase II
Chromosomes (two chromatids) condense and become visible, nuclear envelope breaks down, spindle formation begins
What happens during Metaphase II
Individual chromosomes assemble on the metaphase plate. Due to crossing over, chromatids are no longer identical so there is independent assortment and more genetic variation
What happens in Anaphase II
Chromatids are pulled apart
What happens in Telophase II, What happens after
Chromatids assemble at the poles, chromosomes uncoil and and form chromatin, nuclear envelope reform and nucleolus becomes visible
Cytokinesis - divisions of cells form four genetically different haploid daughter cells.
Why are the four daughter cells at the end of meiosis genetically diffrent?
Independent assortment - Maternal and parental chromosomes face either poles during metaphase
Crossing over - Chromosomes entangle, during Prophase I and anaphase I, During anaphase I, parts of the chromatids break of and re-join (called Chiasmata), these are recombinant chromatids, with genes being exchanged
Mutation - random mutation can cause genetic variation
What is specialisation?
unspecialised cells become specialised and have different roles
How are Erythrocytes (red blood cells) specialised
flattened biconcave shape - increases surface area to volume ratios
no nucleus - increases space for haemoglobin, so more oxygen can be carried
Flexible - able to fit through capillaries
How are Neutrophils (white blood cells) specialised?
Multi-lobed nucleus - easier for them to move through small gaps and get to site of infection
Granular cytoplasm - contain many lysosomes used to attack pathogens
How are sperm cells specialised?
Flagellum - capable of movement
Contain many mitochondria - supply energy for swimming
Acrosome (head) contains digestive enzymes - digest protective layers around the ovum
How are palisade cells specialised?
Contain chloroplasts - absorb large amounts of light
Rectangular shaped - closely packed together
Thin cell walls - increase rate of diffusion of CO2
Large vacuole - maintain turgor pressure
Chloroplasts can move in the cytoplasm to absorb more light
How are root hair cells specalised?
Long extensions - increase surface area, maximising uptake of water and minerals
How are guard cells specialised?
When guard cells lose water and becomes less swollen they change shape - stomata closes to prevent further water loss
What is a tissue?
Collection of differentiated cells that have specialised function
What are the four main category’s of tissues in animals
Nervous - electrical impulses
Epithelial tissues - cover body surfaces (internal and external)
Muscle tissue - adapted to contract
Connective tissue - adapted to hold other tissues together or act as a transport medium
What is the squamous epithelium, how is it adapted? One example
Flat and Thin - one cell thick, allows for rapid diffusion
Alveoli - needs diffusion of oxygen and carbon dioxide
What is the ciliated epithelium , how is it adapted? One example
Hair-like structures called cilia
Goblet cells - release mucus to trap unwanted particles
Bronchi - prevent pathogens or bacteria reaching the alveoli
What is the cartilage , how is it adapted? One example
Contains fibres of of elastin and collagen
Firm and flexible - prevents end of bones rubbing together
Trachea - prevents collapse
What is the muscle , how is it adapted? One example
Need to contract and relax
What is the Epidermis, how is it adapted?
layer of cells on surface of plants,
covered by a waxy cuticle - prevents water loss
Stomata - allow for movement of gasses
What is the Xylem tissue , how is it adapted?
responsible for transport of water and minerals
Composed of dead cells and strengthened by lignin - provides structural support
What is the phloem tissue, how is it adapted?
Responsible for transport of nutrients
Composed of sieve tube cells
What is an organ
collection of tissues that are adapted to perform a particular function
What is an organ system?
composed of many organs working together working together to carry out a function in the body
What are three examples of organ systems
Digestive system
Cardiovascular system
Gaseous exchange system
What are stem cells
Undifferentiated cells
Stem cells loose the ability to do what once they become specialised
Divide, they enter the G0 phase of the cell cycle
What is stem cell potency
Cells ability to differentiate into different cells
What is totipotent?
Cell can differentiate into any type of cell.
Give an example of a totipotent cell
A zygote, or the first 8-16, egg cells from the first few mitotic divisions
What is a pluripotent cell
Can form all tissue types but not the whole organisms
Give an example of a pluripotent cell
Early embryos
What is a multipotent cell
Can only form a range of cells within a certain types of tissue
Give an example of a multipotent cell
Hematopoietic stem cells in bone marrow, produce various types of blood cell
Why is it important that cells differentiate?
They can become adapted to a specific role, and become more efficient
Why is it important that red blood cells be replaced? How many are made per day
short lifespan - around 120 days
Around 3 billion per kilogram per day
Why is it important white blood cells are replaced. How many are made per hour, why might this increase?
Short life span - 6 hours. Produce 1.6 billion per hour, increases during infections
What are two sources of Animal stem cells
Embryonic stem cells - very early stage = totipotent, After 7 days, a blastocyst has formed = pluripotent
Adult stem cells - found in specific areas, multipotent
Where are plant stem cells found, what type of stem cells are these?
Meristem tissue - wherever growth occurs in plants (roots and shoots)
Between phloem and xylem tissues, these are pluripotent
What could stem cells be used for?
Heart disease, type 1 diabetes, Parkinson’s disease, Alzheimer’s disease, macular degeneration, birth defects, spinal injuries, burns, drug trials, development biology
How are embryonic stem cells harvested
Left over embryos from IVF
Why are embryonic stem cells better then adult stem cells
Pluripotent, so can differentiate into any stem cell
Give both sides of embryonic stem cells
For - can help cure life altering diseases, like Alzheimer’s and type 1 diabetes
Against - involves destruction of ‘possible life’.
What are the medical uses of plant stem cells
Medical drugs can be created from stem cells, for cheap
