cell divison (2.0)

cell continuity

when cells develop from other existing cells

cell cycle

series of events that take place between one cell division and the next

cell cycle three phases

interphase, nuclear division, cytokinesis

chromosome structure 

dna and protein

chromatin

elongated chromosomes

haploid cell

one set of chromosomes

function of haploid cells and how 

sexual reproduction as they can fuse with each other 

diploid cell

two sets of chromosomes

homologous pairs 

chromosomes with similar genes that occur in pairs 

interphase def

phase of life cycle of cell when its not dividing

what happens in the interphase

cell is getting ready for mitosis, so its producing identical copies of everything

2 processes involving dna in the interpahse 

dna replication, transcription

other cellular processes occurring in the interphase

photosynthesis, respiration, protein synthesis

two types of molecules formed during the interphase

protein, carbs

dna replication def

process of producing two identical copies of DNA from one original dna molecule

why does dna replication occur 

so mitosis can occur

what, broadly, happens in dna replication (one sentence summary)

single stranded chromosome makes an exact copy of itself to form a double stranded chromosome

events of dna replication

double helix unwinds, two strands of the original double helix separate, incoming bases attach to exposed complementary bases (A - T, G -C), each new double strand rewinds to form a double helix, two new identical strands of dna are formed

complementary bases in dna replication ? 

A TO C, G TO C 

enzyme that catalyses dna replication

DNA polymerase

chromatid

one of the two single identical strands formed after DNA replication

centromere 

point at which two chromatids are held together 

mitosis

is a form of nuclear division in which one nucleus divides two form two identical nucleuses, containing the same number of chromosomes and identical genes

function of mitosis in single cell organisms

asexual reproduction

function of mitosis in multi cellular organism 

growth and repair of cells 

where does mitosis occur in plants

meristem

how does a single cell zygote divide and develop into an embryo

mitosis

4 stages of mitosis 

prophase, metaphase, anaphase, telephase 

what happens in prophase

chromosomes contract and become visible double stranded chromosomes

two spindle fibres appear

nuclear membrane starts to break down

what happens in the metaphase

spinde fibre from each pole attached to each centromere 

chromosomes line up along the equator of the cell

what happens in the anaphase

spindle fibres contract

double stranded chromosomes separate, and are pulled to each end of the cell

telephase events

spindle fibre breaks down

chromosomes at each pole elongate

nuclear membrane forms around each of the chromosomes

two nuclei are now identical

cytokinesis 

dividing of the cytoplasm to form two separate cells immediately after mitosis 

cytokinesis in animal cells

cleavage furrow forms

shallow grove becomes deeper, until it divides the cytoplasm and the cell splits into two

cytokinesis in plant cells

cell plate forms

vesicles containing mainly cellulose forms new cell walls, these join together to form a cell plate

what is cancer 

group of disorders in which certain cells LOSE THEIR ABILITY TO CONTROL the rate of mitosis, and how many times it can occur 

characteristics of cancer cells

dont stop growing and dividing by mitosis

dont stick together (allowing them to spread)

dont repair themselves

what is a tumour

mass of cells that occur when a cell loses its ability to control the rate of mitosis

types of tumours 

benign, malignant 

what is a benign tumour

cells stop dividing after some time, dont spread

(eg warts and skintags)

malignant tumours

dont stop growing

may be life threatening as they invade other cells

move from place to place in body

oncogens def 

cancer forming genes 

carcinogens

cancer causing agents

carcinogen examples

asbestos, uv rays, cigarette smoke

causes of cancer 

Infectious agents (HPV)

Environmental factors (cigarettes, radon gas)

genetic susceptibility 

how do infectious agents cause cancer

alter genes controlling cell division, surpress a persons immune system

how does age contribute to developing cancer

build up of mutations over time

genes that increase risk of cancer 

BRCA1 and BRCA2

four steps to preventing and treating cancer

early detection, treatments, vaccinations, lifestyle changes

meiosis

form of nuclear division where the four daughter nuclei contain half the chromosome number of the parent nucleus

what does meiosis cause 

number of chromosomes in the parent cell to be halved, genetic variation

role of meiosis

produces gametes, allows for greater variation