Cell Division Flashcards
Specialised cells
Cells are differentiated specialised to carry out specific functions
Erythrocytes
RBCs - flattened biconcave shape increase sa to vol ratio essential for O2 transport
No organelles space for haemoglobin
Flexible to squeeze through capillaries
Neutrophils
A type of wbc
Multi loved nucleus making it easier to squeeze through small gaps to get to infections
Cytoplasm= many lysosomes that contain enzymes to attack pathogens
Sperm cells
Tail capable of moving to egg
Many mitochondria for energy to swim
Acrosome(head) contains digestive enzymes to penetrate egg
Palisade cells
In mesophyll later
Contain chloroplast to absorb large amounts of light
Rectangular to closely pack
Thin walls diffusion of CO2 easy
Large vacuole to maintain turbot pressure
Chloroplasts can move
Root hair cells
Large sa to vol ratio maximising uptake of water and mineral from soil
Guard cells
Form stomata
Guard cells lose water - change shape stomata closes
Cell wall thicker on one side so doesn’t change shape symmetrically
Tissue catergories
Nervous
Epithelial
Muscle
Connective
Squamous epithelium
Very thin and flat 1 cell thick
forms lining of the lungs
Present when rapid diffusion across surface is essential
Ciliates epithelial cells
Cilia on surface move in rhythmic manner to sweep mucus from lungs
Goblet cells present to release mucus to trap unwanted shit reaching the alveoli
Cartilage
Connective tissue
Fibres of elastin and collagen
Chondrocyte cells embedded in extra cellular matrix
Prevents ends of bones from rubbing
Tissues in plants
Epidermis
Vascular
Epidermis
Single layer of closely packed cells covering surfaces of plants
Covered by waxy cuticle layer to reduce water loss
Stomata present to allow CO2 in and out and oxygen and water out
Xylem and phloem tissue
Vascular tissues found in stems of plants to transport needed materials
Stem cells
Undifferentiated cells
Able to undergo continuous cell division
Source of new growth development and tissue repair
When specialised lose ability to divide
Potency
A stem cells ability to differentiate into different cells
Totipotent
Can differentiate into any type of cell
Fertilised egg or zygote and 8/16 cells from first mitotic devisions
Destined to produce a whole organism
Pluripotent
Stem cells can form all tissue types but not whole organisms
Present in early embryos
Origin of different types of tissue within organism
Multi potent
Stem cells that can only form a range of cells within certain tissue type
Eg haematopoetic stem cells in bone marrow are multi because differentiate to various types of blood cells
Replacement of blood cells
RBCs every 120 days stem cells in bone marrow produce 3 bill per kg of body mass per day
WBCs live for 6 hours and produced at 1.6 billion per kg per hour increasing during infection
Sources of animal stem cells
Embryonic stem cells- totipotent stem cells 7 days later blastocyst forms pluripotent cells
Adult stem cells- bone no arrow multi potent also in umbilical cords - invasive surgery not needed and stored just in case needs in future (no rejection)
Sources of plant stem cells
Meristematic tissues
Tips of roots and shoots (apical meristems)
Located between xylem and phloem called cambium - differentiate into vascular tissue
Constant pluripotent
Uses of stem cells
Heart disease - replace muscle tissue
Type 1 diabetes- stem cells form beta cells
Parkinson’s - form dopamine producing cells in brain
Alzheimer’s - differentiate form new brain cells
Macular degeneration- stem cells in blindness
Birth defects- reverse untreatable birth defects
Spinal injuries - rats spines rebuilt using stem cells
Treating burns
Drug trials
Ethics
Embryonic stem cells in therapies
Destruction of embryo to extract stem cells - this is murder and religious objections embryo has rights etc
Cell cycle
Interphase
Mitotic phase
Interphase
Long periods of growth and normal working separate divisions
- Dna is replicated and check
-Protein synthesis occurs in cytoplasm
- mitochondria and chloroplast grow and divide
- normal metabolic processes
Interphase stages
G1- proteins from organelles are synthesised and produced - replicate
S- synthesis dna is replicated in the nucleus
G2- duplicated dna checked for errors and cell increase in size and energy stores increased
Mitosis
Cell division
Mitosis - nucleus divides
Cutokinesis- cytoplasm divides and 2 cells are produced
G0
Phase when the cell leaves the cycle
- differentiation = cell specialised no longer able to divide
- dna may be damaged no longer viable all cells eventually become senescent (deteriorate)
-No of these cells increase w age- cancer
Only few can return to cycle eg lymphocytes
Controlling cell cycle
Ensure cell only divides when grown to right size
Checkpoints control mechanisms control and verify before progressing
G1 check - if correct trigger dna rep
G2 check - dna check cell initiates mitosis
Metaphase checkpoint - mitosis when all spindles attach to chromo in lines
Chromatids
All dna in nucleus replicated in interphase each chromosomes converted into 2 dna molecules - chromatids
Centromeres
Chromosomes joined together at a region called centromeres
To keep chromo together during mitosis so precisely manoeuvred and equally split into 2 daughter cells
Stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Prophase
Chromatin fibres(proteins dna and rna) coil and condense to form chromosomes
Nucleolus and nucleus membrane disappear
Microtubules make spindles linking poles of cell
Centrioles opposite ends help form spindles- attach to centromeres and move chromosome to the middle
Metaphase
Chromosomes are moved to form a plane in the centre of the cell all in line forming metaphase plate and held in position
Anaphase
Centromeres divide and chromatids are separated by shortening spindle fibres
V shape drag by centromeres through cytosol
Telophase
Chromatids reach poles and are called chromosomes
2 new sets of chromo and nuclear envelope reforms
Cytokinesis
Starts during telophase
Actual splitting into 2 separate cells
Animal = cytoskeleton pulls membrane inwards until close enough to fuse
Plant = vesicles from Golgi assemble in middle and fuse with each other and the cell surface membrane dividing into 2 wall forms here
Meiosis
Process in which gametes are formed
Produce 4 daughter cells
Occur in diploid cells
Fuse mother and father gametes so half no of chromosomes required
Stages of meiosis
Meiosis 1 - first div pairs of chromosomes separated into 2 cells each containing 1 full set instead of two
Meiosis 2 - pairs of chromatids spectated forming 2 more cells
Prophase 1
Homologous chromosomes link together forming chiasmata (bivalents )
1x maternal pair 1x paternal pair
crossing over takes place exchanging certain alleles
Metaphase 1
Homologous pairs aligned on metaphase plate
Orientation of each homologous pair is random cannot predict whether the paternal or maternal chromosome will end up in what gamete - independent assortment
Anaphase 1
Chromosomes are pulled to opposit poles
Sections of crossovers break off and join (chiasmata) resulting in exchange of DNA
Forms recombinant chromatids - combo different to original chromatids
Forms genetic variation
Telophase 1
Chromosomes assemble at each pole and nuclear membrane reforms
Cytokinesis occurs
Diploid to haploid is complete
Prophase 2
Chromosomes condense and become visible
Spindle formation begins
Metaphase 2
Individual chromosomes assemble on metaphase plate
Due to crossing over chromatids are no longer identical independent assortment
Anaphase 2
Chromatids of Individual chromosomes pulled to opposite poles after division of centromeres
Telophase 2
Chromatids assemble at poles
Nuclear envelope reforms
Cytokinesis forms 4 daughter cells genetically different due to crossing over and independent assortment
Chiasmata
Homologous pairs link together to form this
Breaks in anaphase 1 exchanging alleles
Independent assortment
Orientation of homologous chromosomes are random and cannot predict what chromosome will end up in the gamete whether it be maternal or paternal
result in many different combos of alleles facing the poles
How does sexual reproduction lead to genetic variation
Variety of alleles inherited more than one parent
Random fertilisation
Meiosis produces genetically different gametes
Crossing over in prophase 1
Independent assortment in meta 1
