6 - Cell division Flashcards
Cell cycle stages (5)
M G0 G1 S G2
What happens in the M phase of the cell cycle? (3)
Cell growth stops
Mitosis (PMAT)
Cytokineses
What happens in the G0 phase of the cell cycle?
The cell may go through:
Apoptosis (programmed cell death)
Differentiation
Senescence (cell can only divide a certain n.o of times)
Some cells can be in the cycle indefinitely
What happens in the G1 phase of the cell cycle? (4)
Cell grows
TRANSCRIPTION of genes - make RNA
Protein synthesis
Organelles duplication
G1 CHECKPOINT (4)
CHECK FOR: cell size DNA damage growth factors nutrients
What happens in the S phase of the cell cycle? (4)
DNA replicates
|—-> therefore each chromosomes has a pair of identical sister chromatids.
Phase happens quickly
|—-> because the exposed DNA are exposed and are susceptible to mutagen agents.
What happens in the G2 phase of the cell cycle? 5
Cell grows
Protein microtubles reassemble into spindle fibres.
G2 CHECKPOINT (3)
CHECK FOR:
cell size
DNA replication
DNA damage
Stages of mitosis (4)
Prophase
Metaphase
Anaphase
Telophase
Interphase
During interphase:
DNA replicated and checked
Protein synthesis occurs in the cytoplasm
Mitochondria grow and divide
Prophase
prepare
Chromosomes copied to form 2 chromatids
Chromosome condense
Nuclear envelope breaks down
Centrioles move to opposite poles of the cell
Spindle fibres extend to the middle of the cell
Metaphase
middle
Chromosomes line up at the equator of the cell forms metaphase plate.
Spindle fibres attaches to the centromere of the chromosomes.
Anaphase
away
Spindle fibres contract - split the centromere - chromatids are separated - dragged to poles - centromere lead
Complete set of chromosomes at each pole
Telophase
two
Chromatids reach the poles and uncoil
Nuclear envelope reforms - forming 2 nuclei
Cytokinesis follows
Importance of mitosis (3)
Assexual reproduction
Growth of cells
Replication and repair of cells
Importance of Meiosis (1)
To produce sex cells (gametes)
Prophase I
Chromatin condense & chromosome supercoils
Nuclear envelope breaks down
Chromosomes are in HOMOLOGOUS pairs = Bivalents
Chromatids entangle = Crossing over
Metaphase I
Chromosomes attach at the equator of the spindle - joined at the centromere
The homologous pairs are arranges randomly = Independent assortment
Anaphase I
Members of each homologous chromosomes are pulled apart by motor proteins
The crossed-over areas separate at the chiasmata leading to an area of swapped alleles/chromosomes
Telophase I
Two new nuclear envelope form and the cell divides via cytokinesis
Each new nucleus has half the number of chromosomes as the original but still has two chromatids.
Prophase II
The nuclear envelope breaks down
Chromosome coil and condense
The chromosomes are no longer identical due to the crossing over from P1 = Independent assortment
Spindle forms
Metaphase II
The chromosome attach to the spindle (by the centromere) and pilled to the metaphase plate
Chromatids are randomly arranged
Anaphase II
Centromeres divide
Chromatids are pulled apart by motor proteins - towards the poles
Chromatids are randomly segregated
Telophase II
Nuclear envelope form around 4 haploid cells
Differentiation
Process which stem cell become specialised into different types of cells.
Erythrocytes
(Red Blood Cells)
ANIMAL
Function: Transport oxygen around the body
Features:
Biconcave shape - increase surface area to volume ratio
Flexible - Squeeze through nervous capillaries
Neutrophills
(White Blood Cells)
ANIMAL
Function: ingest invading pathogens
Features:
Multi-lobbed nucleus
Attracted to infection sites by chemotaxis
Granular cytoplasm —> contains lysosomes —> contains enzymes —> which attack pathogens
Spermatozoa
ANIMAL
Function: Deliver genetic material to the female gamete
Features:
Flagellum - move quicker/easier
Many mitochondria - provide energy and propel the cell
Acrosome - contains digestive enzymes —> digest layers around the ovum —> allow sperm to penetrate
Palisade Cells
PLANT
Function: Absorb large amount of light for photosynthesis
Features:
Cells are rectangular - easy top pack many in a continuous layer
Thin cell wall - increased rate of diffusion
Large vacuole - to maintain turgor pressure
Root Hair Cells
PLANT
Function: Absorb water and mineral ions from the soil
Features:
Long root hairs - to maximise the water uptake from the soil
Guard Cells
PLANT
Function: Necessary for CO2 to enter the plant for photosynthesis to occur
Features: lose water —> less swollen —> more osmotic forces
4 main tissue types
Epithelial
Connective
Muscle - made of cells specialised to contract and move
Nervous - made of cells specialised to conduct electricity
Squamous Epithelium
Function: Allows diffusion to occur
Features:
Thin, flat cells - allows rapid diffusion
Forms the lining of the lungs allows diffusion of oxygen into the blood
Ciliated Epithelium
Function: Traps and swipes away bacteria
Features:
‘Hair-like’ structure - move together not allowing substances to pass
Goblet cells —> release mucus = trap any unwanted particles
Cartilage
Function: Prevents bones from rubbing against each other causing damage
Features:
Firm, flexible - composed of chondrocyte cells
Contains proteins - elastin and collagen
Muscle
Function: Helps move and support the body
Features:
Can contract - to move bones —> to move the body
Epidermis
Function: Covers the surface of plants
Features:
Waxy cuticle - reduce water loss
Xylem & Phloem
Function: Responsible for transport of water/minerals via the cell. Responsible for transport of organic molecules.
Features:
Elongated,dead cells
Strengthened with lignin - provides support for the plant
Sieve tubes - separates the sieve plates
Stem Cells
Undifferentiated cells that are not specialised.
Undergo cell division repeatedly
Stem cells are necessary for …
Growth
Development
Tissue repair
Do stem cells need to controlled? Why?
If stem cells do not divide fast enough then tissues are not replaced efficiently enough = ageing
uncontrolled divisions –> form tumors –> development of cancer
Stem Cell Potency
The stems cells ability to divide into different cell types
Greater of number of cells = greater potency
Totipotent
These stem cells can differentiate into any type of cell
Pluripotent
These stem cells can form all tissue types but NOT whole organism
Multipotent
These stem cells can only form a range of cells within a certain tissue type
Replacement of erythrocytes
Short lifespan around 120 days therefore need to be replaced constantly
Bone marrow produces 3 billion/kg (body mass) to keep up with the body
Replacement of neutrophils
Live for 6 hours
Produce 1.6 billion/kg/hr
This increases during infection
Embryonic Stem Cells
Present a a very early stage of embryo development and are totipotent
Tissue Stem Cells
Present in life from birth
Stem cells can harvest in the umbilical cord
Sources of plant stem cell
Present in meristematic tissue in plants.
Located between the phloem and the xylem this is called vascular cambium
Stem cells have been transported into certain areas to help treat patients, certain diseases;
Heart disease Type 1 diabetes Parkinson's disease Alzheimer's disease Muscular degeneration Birth defects Spinal injuries
Also stem cells are used in:
The treatment of burns
Drug trails
Developmental biology
Ethics of stem cells:
Embryos were donated by those left over after fertility treatment by the new law dictates that the embryos be created in a lab.
This holds back the success of treatment of incurable diseases
