2.1.6 cell division, cell diversity and cellular organisation

2.1.6 cell division, cell diversity and cellular organisation flashcards - PMT

what is cell cycle + stages

regulated cycle division w intermediate growth periods

• interphase

• mitosis/meiosis (nuclear division)

• cytokinesis (cytoplasmic division)

stages of interphase

G1: cell synthesises proteins fr replication e.. tubulin for spindle fibres + cell size doubles

S: DNA replicates = chromosomes consist of 2 ister chromatids joined at a centromere

G2: organelles divide

purpose of mitosis

produces 2 genetically identical daughter cells for

• growth

• cell replacement/tissue repair

• asexua reproduction

stages of mitosis

prophase

metaphase

anaphase

telophase

stages of prophase

1. chromosomes condense, becoming visible. (X-shaped: 2 sister chromatids joined at centromere)

2. centrioles move to opposite poles of cell (animal cells) + mitotic spindle fibres form

3. nuclear envelope + nucleolus break down = chromosomes free in cytoplasm

stages of metaphase

sister chromatids line up at cell equator, attached to mitotic spindle by their centromeres

stages of anaphase

requires energy from ATP hydrolysis

1. spindle fibres contract = centromeres divide

2. sister chromatids separate into 2 distinct chromosomes & are pulled to opposite poles of cell. (looks like ‘V’ shapes facing each other)

3. spindle fibres break down

stages of telophase

chromosomes decondense, becoming invisible again

new nuclear envelopes form around each set of chromosomes = 2 new nuclei, each w 1 copy of each chromosome

stages of cytokinesis

cell membrane cleavage furrow forms

contractile division of cytoplasm

how is cell cycle regulated

checkpoints regulated by cell signalling proteins ensure damaged cells don’t progress to next cycle stage

cyclin-dependent kinase enzymes phosphorylate proteins that initiate next phase of reactions

what happens at key cell cycle checkpoints

G1 - S: cell checks for DNA damage. after restriction point, cell enters cycle

G2 - M: cell checks chromosome replication

Metaphase: cell checks that sister chromatids have attached to spindle correctly

what is meiosis

form of cell division that produces 4 genetically different haploid cells (cells w half number of chromosomes found in parent cell) known as gametes

stages of meiosis I

homologous chromosomes pair to form bivalents

crossing over (exchange of sections of genetic material) occurs at chiasmata

cell divides into 2. homologous chromosomes separate randomly. each cell contains either maternal/paternal copy

what are homologous chromosomes

pair of chromosomes w genes at same locus. 1 maternal + 1 paternal. some alleles may be same while others diff

stages of meiosis II

independent segregation of sister chromatids

each cell divides again, producing 4 haploid cells

how does meiosis produce genetic variation

crossing over during meiosis I

independent assortment (random segregation) of homologous chromosomes + sister chromatids. result in new combinations of alleles

how do cells become specialised

some genes are expressed while others are silenced due to cell differentiation mediated by transcription factors. cells produce proteins that determine their structure + function.

what is transcription factor

protein that controls transcription of genes so that only certain parts of DNA are expressed ex. in order to allow cell to specialise

how transcription factors work

move from cytoplasm into nucleus

bind to promoter region upstream of target gene

makes it easier or more difficult for RNA polymerase to bind to gene. this increases/decreases rate of transpiration

what is a stem cell

undifferentiated cells that can divide indefinitely + turn into oter specific cell types

name + definition 4 stem cell types

totipotent: can develop into any cell type inc. placenta + embryo

pluripotent: can develop into any cell type excluding placenta + embryo

multipotent: can only develop into few diff types of cell

unipotent: can only develop into one type of cell

suggest uses of stem cells

• repair of damaged tissue ex. cardiomyocytes after myocardial infarction

• drug testing on artificially grown tissues

• treating neurological diseases e.g. alzheimer’s + parkinson’s

• researching developmental biology e.g. formation of organs, embryos.

describe 2 groups of specialised cells in blood

erythrocytes (red blood cells): biconcave, no nucleus, lots of haemoglobin to carry oxygen

leucocytes (white blood cells): lymphocytes, eosinophils, neutrophils to engulf foreign material, monocytes

how do specialised cells in blood form

multipotent stem cells in bone marrow differentiate into

• erythrocytes, have short lifespan + cannot undergo mitosis since they have no nucleus

• leucocytes inc. neutrophils

relationship between system + specialised cells

specialised cells → tissues that perform

specific function → organs made of

several tissue types → organ systems

describe structure of squamous + ciliated epithelia

simple squamous epithelium: single smooth layer of squamous cells (thin + flat w round nucleus) fixed in place by basement membrane

ciliated epithelium: made of ciliated epithelial cells (column-shaped w surface projections called cilia that move in synchronised pattern)

specialised structure of a spermatozoon

specialised to fertilise an ovum during sexual reproduction in mammals

structure + function of palisade cells and guard cells in plants

palisade cells: specialised to absorb light energy for photosynthesis, so contain many chloroplasts. pack closely together

guard cells: form stoma. when turgid, stoma opens; when flaccid, stoma closes. walls are thickened by spirals of cellulose

structure + function of root hair cells

specialised to absorb water + low conc minerals from soil

hair like projections increase SA for osmosis/carrier proteins for active transport

many mitochondria produce ATP for active transport

what are meristems

totipotent undifferentiated plant cells that can develop into various types of plant cell, inc xylem vessels + phloem sieve tubes

classified as atypical (at root + shoot tips), intercalary (stem) or lateral (in vascular areas)

structure of vascular bundle

xylem + phloem tissue surrounded by cambium (meristematic tissue)

structure of phloem tissue

sieve tube elements: form tube to transport sucrose in dissolved form of sap

companion cells: involved in ATP production for active loading of sucrose into sieve tubes

plasmodesmata: gaps between cell walls where cytoplasm links, allowing substances to flow

primary cell types in xylem tissue

vessel elements: lignified secondary walls for mechanical strength + waterproofing, perforated end walls for rapid water flow

tracheids: tapered ends for close packing, pits for lateral water movement, no cytoplasm or nucleus

additional cell types in xylem tissue

xylem parenchyma: packing tissue with thin walls transmit turgidity

sclereids

sclerenchyma fibres: heavily lignified to withstand negative pressure

structure of cartilage

avascular smooth elastic tissue made of chondrocytes, produce extensive extracellular matrix (ECM)

ECM mainly contains collagen + proteoglycan

3 categories: hyaline, yellow elastic, white fibrous (dpens on ratio cells:ECM)

3 types of muscle in body + location

cardiac: heart

smooth: walls of blood vessels + intestines

skeletal: attached to incompressible skeleton by tendons

gross structure of skeletal muscle

muscle cells fused together to form bundles of parallel muscle fibres (myofibrils)

arrangement ensures no point of weakness between cells

each bundle surrounded by endomysium: loose connective tissue w many capillaries