C6- Cell Division Flashcards
Karyotype
Number and appearance of chromosomes
homologous chromosomes
Chromosomes in a pair that have the same gene order
Slight variation results in alleles
Chromatid
two identical copies of DNA ( chromosomes) held together at the centromere
> < < is a chromatid
Chromosome structure
pair of chromatids
–> identical genetic information
Joined by a centromere
> .<
Chromatin
uncondensed DNA in a complex with histones
histones= proteins
Diploid Cell
Full set of chromosomes, one inherited form each parent
2n= 23 x ><
4n= 23 x >< ><
Cell cycle
general
3 stages
sequence of cell growth and division
interphase = Cell growth
Mitosis or meiosis = Chromosomes divide
Cytokinesis = Cytoplasm divides
Haploid cells
single set of unpaired chromosomes
n = 23x >
Interphase
G1
Growth 1
Cellular components duplicate
–> e.g ribosomes duplicate
Interphase
S phase
Synthesis
Chromosomes duplicate
–> to a pair of chromatids
Interphase
G2
General order
Growth 2
ATP levels increase
Cell checks duplicated chromosomes for error, making any needed repairs
G1, (G0), S, G2
Interphase
G0
Growth Zero
Cells leave cycle temporarily or for good
–> differentiation or specialisation
DNA Damage, cell can no longer divides
–> hits permanent arrest
Hayflick Limit
The finite number of times a cell can divide
- Limit is reduced by cortisol ( stress hormone)
Telomere
Protects gene, slightly damaged/lost every division
Mended by telomerase, which is inhibited by cortisol
Therefore, cortisol reudces the Hayflick limit
PMAT
Prophase
Metaphase
Anaphase
Telophase
Functions of mitosis
Growth
Repair
Asexual reproduction
Prophase
Chromatin coils and condenses into visible chromosomes
nucleolus disappears
nuclear membrane breaks down
centrioles migrate to poles of the cell
spindle fibres attach to centromeres and begin to move chromosomes
nuclear envelope disappears
Metaphase
Chromosomes moved by spindle fibres to the equator of the cell
chromosomes lined up in a plane called the metaphase plate
Anaphase
The centromeres that hold the pair of chromatids together divide
chromatids are separated
spindle fibres shorten
chromatids pulled to opposite poles
V shape of chromatid caused by centromere being pulled
Telophase
Centromeres that join chromatids reach poles
Chromatids now chromosomes
nuclear envelope reforms around chromosomes
chromosomes uncoil
nucleolus formed
cytokinesis begins
Cytokinesis
The actual division of the cell into two separate cells
Cytokinesis
Plant cells
Vesicles assemble where the metaphase plate was formed
vesicles fuse with each other and cell surface membrane
Cytokinesis
Animal cells
Cleavage furrow forms at the middle of cell.
Cell Surface membrane pulled inwards by cytoskeleton until close enough to fuse around the middle, forming two cells
Meiosis II
Key differences
P- Chromosomes ( 2 chromatids) unlike I
–> Like mitosis
M- independent assortment
A- individual chromatids
T- 4 genetically different daughter cells formed
Meiosis II
independent assortment of sister chromatids
each cell divides again- 4 haploid cells formed
Meiosis I
homologous chromosomes pair up to form bivalents
Crossing over ( exchange sections of genetic material, occurring at chiasmata)
Cell divides into two, homologous chromosomes separate randomly
–> maternal or paternal copy
how is the cell cycle regulated
Checkpoints regulated by cell signalling proteins ensure damaged cells do not progress to next stage of cycle
Between G1 and S = Check for DNA damage
G2 and M = Check chromosome replication
Metaphase= Sister chromatids attached to centromere correctly
What is meiosis
From of cell division that produces 4 genetically different haploid cells known as gametes
Meiosis
Prophase 1
Similarities= chromosomes condense, nuclear envelope dissolves, nucleolus disappears, spindle formation begins
Differences= Homologous chromosomes pair up, forming bivalents
chromatids entangle and cross over
Meiosis
Metaphase I
Independent assortment of homologous pairs
Maternal/ paternal chromosomes end up facing the poles
Genetic variation
Meiosis
Anaphase I
Homologous chromosomes are pulled to opposite poles and chromatids stay joined together
Sections on chromatids entangle, break off and re-join, may result in exchange of DNA
–> happens on chiasmata
Meiosis
Metaphase II
Different form metaphase I
–> individual chromosomes assemble on metaphase plate
independent assortment
Meiosis
Genetic variation
Crossing over during Meiosis I
Independent assortment of homologous chromosomes and sister chromatids
New combination of alleles
Chiasmata
Sections of DNA entangle during crossing over, break and re-join during Anaphase I
Results in exchange of DNA between bivalent chromosomes
–> genetic variation
Organs and organ systems
Group of tissues/ organs working together to perform a specific function
Specialised cells
Erythrocytes
RBC
Flattened biconcave shape, increases surface area to volume ratio, so RBC can transport more O2
No nucleus or mitochondria= more space for haemoglobin
Flexible- squeeze through narrow capillaries
Specialised cells
Neutrophils
WBC
Multilobed nucleus= easier to squeeze through small gaps to get to infection site
Granular cytoplasm, many lysosomes that contain enzymes to attack pathogens
Specialised cells
Sperm cells
Flagellum for movement
Many mitochondria to provide energy for swimming
Acrosome contains digestive enzymes to digest outer layers of ovum to penetrate for fertilisation
Cells
Tissues
cells= basic unit of life
Tissues= group of differentiated cells working together to perform a specific function
Stem cells
Undifferentiated cells
- can replicate many times
- Potential to become different types of cells
Stem cell potency
Totipotent- capable of giving rise to any cell type or complete embryo
Pluripotent- capable of giving rise to any tissue type but not whole organisms
Multipotent- capable of giving rise to only a range of cell types
Sources of animal stem cells
Embryonic-
early stages of embryo development- totipotent
After 7 days, changes to a blastocyst, now pluripotent
Adult- present throughout life
multi potent
found in bone marrow and umbilical chords
sources of plant stem cells
Meristematic tissue
- roots/ shoots= apical meristem
Cambium= wall between phloem and xylem
uses of stem cells
Drug trails- test for efficacy and toxicity
Study of developmental biology
Burn treatments
Parkinson’s
Spinal injuries
Stem Cells
Ethics
Leftover IVF embryos
Religious and moral obligations
–> debate about when life begins
Embryo cannot give consent
Uses up leftover umbilical chords
Specialised tissue
Squamous epithelium
Thin
–> one cell thick
Forms lining of lungs, allowing raid diffusion of oxygen into blood
Specialised tissues
Ciliated epithelium
Cilia on surface move in rhythmic manner
Trachea- Sweep away mucus form the lungs
Goblet cells- secrete mucus
Specialised tissues
Cartilage
Contains fibres of proteins elastin ad collagen
Prevents end of bones form rubbing and causing damage
–> connective tissue
Specialised tissues
Muscle
Skeletal muscle ( muscle to bone)
Contains myofibrils- contractile proteins
Specialised tissues
Plant epidermis
Adapted to cover plant surfaces
Covered by waxy cuticle
–> reduces water loss
Guard cells- control stoma opening size
