Biology D2.1 cell division

cytokinesis

for daughter cells to separate, cytoplasm of parent cell must split between daughter cells, both daughter cells must receive at least one mitochondria and organelles that can only be made by dividing a pre-existing structure

cytokinesis animal cell

in animal cell network of myosin and actin proteins form a contractile ring that pinches cell membrane together

cytokinesis plant cell

in plant cells involves assembly of cell plate formed from fusion of vesicles containing cell wall material, grows outward until reaches existing cell wall which it fuses with

oogenesis

process of producing mature egg cells in humans, primary oocyte undergoes two round of cell division resulting in secondary oocyte and polar body in first round, if fertilised undergoes second round of division producing mature ovum and second polar body, polar body usually disintegrates and gets reabsorbed by the body, large size and more cytoplasmic content essential for necessary nutrients and machinery for fertilisation and early embryonic development

budding yeast

asexual reproduction, outgrowth of genetically identical daughter cell or bud from parent cell, bud start small and grows, usually receives less than half of cytoplasm

mitosis

somatic cells and produces diploid daughter cells, genetically identical to parent, I eukaryotes produces cells for growth or to replace lost or damaged cells

meiosis

four haploid genetically unique daughter cells which will form gametes, genetically unique due to crossing over and independent assortment, two rounds of nuclear division

DNA reolication

occurs in interphase, after each chromosome replicated, consists of two genetically identical sister chromatids held together by centromere, at beginning of nuclear division chromatin is supercoiled and condensed by histones results in chromosomes allowing efficient separation of replicated DNA, microtubules and microtubule motors move the chromosomes

Mitosis prophase

chromatin condenses to chromosomes each chromosome has been replicated prior, nuclear membrane breaks down and spindle fibres form

mitosis metaphase

sister chromatids line up on the metaphase plate, spindle fibres bonded to centromeres move them into position

mitosis anaphase

spindles shorten, splitting centromere pulling chromatids to opposite poles of the cell

mitosis telophase

chromosomes decondense nuclear membrane reforms at each pole, spindles disintegrates and cell elongates for cytokinesis

prophase 1

nuclear membrane breaks down and spindle fibres form , chromatin condenses to chromosomes forming sister chromatids (bivalent) pairs of chromatids called homologous pairs, once bivalent forms crossing over can start, exchange f equivalent segments of DNA between non-sister chromatids, results in sister chromatids non-genetically identical

homologous chromosomes

similar in size, shape and same genes at same location although can have different alleles for a gene

anaphase I

unlike mitosis, sites chromatids remain connected at centromere and move to same pole, bivalents are separated

Non- disjunction

genetic error that can happen in meiosis, either failure of homologous pairs to separate during anaphase I or failure of sister chromatids to separate at anaphase II, leading to gametes to extra or missing chromosomes, can also happen in mitosis but effects are rarely noticeable

one extra and one less

trisomy, monosomy, can occur in any of the 23 chromosome pairs, severity depend of chromosome effected, Trisomy 21 (Down syndrome extra copy of chromosome 21)

chiasmata (chiasma)

points where crossing over occurs, can occur almost anywhere

recombinant chromatids

chromosomes that have undergone crossing over

random orientation

during metaphase I homologous chromosomes line up on equator orientated randomly (2^n) also occurs in metaphase 2

cell proliferation

process of cellular division and replication for growth, cell replacement and tissue repair

growth

cell proliferation needed for increase in cell number and or organism size and complexity

cell proliferation plants

growth in concentrated in regions Called meristems in tips of roots and shoots (undifferentiated cells), cells in meristems actively divide and differentiate providing cells needed for extension of roots, stem and development of leaves

animal embryonic division

cells divide rapidly in early embryonic development cell divides approx every 24h, called cleavage, involves division of fertilised egg into multiple totipotent cells (blastomeres)

cell replacement

occurs as routine in replacing skin which is constantly renewing itself in process called skin turnover

tissue repair

important in wound healing, responsible for growth and repair of damaged tissue

stages of cell cycle

Interphase: Gap 1, synthesis, gap 2, followed by mitosis and cytokinesis

G1

cells grow in size, carries out normal metabolic functions including protein synthesis, mitochondria and chloroplasts reproduce through binary fission , cel approx doubles in size, also a checkpoint where cell checks its internal environment to make sure its ready for DNA synthesis

Synthesis

DNA replication occurs

G2

cell continues to grow and prepare for mitosis by synthesising microtubules and other proteins required for nuclear and cellular division, also a checkpoint that DNA replication was successful

cyclins

family of proteins that controls cell cycle, they bind to and activate cyclin- dependant kinases, a group of enzymes that phosphorylate specific proteins to drive the cell cycle forward, each cyclin only activates during specific stages of the cycle and must reach certain threshold for cell to progress to next stage

proto- oncogenes

genes that code for proteins that help promote cell growth and division

tumour suppressor genes

genes that code for proteins that which normally slow or prevent cell division

mutations in genes that control cell division

in proton-oncogenes or tumour suppressor genes can cause uncontrolled cell division by the overproduction of certain cykilns , protooncognes leads to proteins being over expressed can lead to uncontrolled cell division, the mutated genes is now called an oncogene, tumour.. can promote programmed cell death (apoptosis)

tumours

uncontrolled cell division can lead to accumulation of abnormal mass of cells called tumour, they are derived from body’s own cells so immune system might not recognise them as abnormal, they can also secrete signalling molecules that stimulate development of blood vessels which supply nutrients and oxygen to growing mass of cells

bening tumours

growth of abnormal cells that are not cancerous , have well defined boarders and do not spread to other parts of the body, may still require treatment, can usually be successfully surgically removed if let untreated big, rarely transforms to malignant

malignant tumours

are cancerous, grow an divide more rapidly, often lack well defined boarders, so difficult to remove completely . can spread through bloodstreams or lymphatic systems through metastasis, when a malignant tumour metastasises the original tumour called the primary tumour, the one that spreads from it is the secondary tumour , usually more difficult to treat, usually target with combination of treatment eg surgery, radiotherapy, and chemotherapy

mitotic index

measure of proportion of actively dividing cells in a population, expressed as a value between 0 and 1 or percentage, more proliferation higher mitotic index