Cell Division Flashcards
what is cell cycle?
cellular events, that repeat in order between one cell division and the next. occurs in all body cells of multicellular organisms
what are the 3 stages in cell cycle?
interphase - cell growth, DNA replicates, cell organelles replicate, ATP is built up
mitosis- nucleus divides forming 2 genetically identical daughter nuclei
cytokinesis- cytoplasm divides to form 2 daughter cells
how much of the cell cycle is interphase ?
90%
another name for interphase?
resting stage
interphase
period of intense biochemical activity
what 3 stages is interphase subdivided into?
G1= cell increasing in size
Synthesis= DNA replicates, checking DNA for errors
G2= cell keeps increasing in size, protein synthesis, ATP stores built up
when does amount of DNA double?
at interphase
when are chromosomes visible?
when cell is dividing, otherwise they consist of a widely spread area of darkly stained material called chromatin
what are chromosomes in eukaryotic cells made up of?
70% protein(histones)
15% DNA
10% RNA
how many strands is a chromosome made up of ?
made up of 2 strands ( as DNA replicated in interphase) called sister chromatids joined by a centromere
what is loci?
where the gene is
how many chromosomes do humans have?
46 - half from father half from mother
23 and 23
what is ploidy level?
number of complete sets of chromosomes in an organism
what feature is used to put chromosomes in order?
size order
term used for ‘matching’
homologous
what pairs are autosomes?
1-22
what is the 23rd pair?
sex chromosomes
what chromosomes do males have?
X + Y
what chromosomes do females have?
X + X
photograph used for chromosomes?
karyotype
what is mitosis?
type of cell division in which two daughter cells have the same number of chromosomes and are genetically identical with each other and the parent cell
= giving genetic stability
mitosis is needed in multicellular organisms for ?
genetic stability
growth of tissues
repair/replacement of tissues
asexual reproduction
stages of mitosis
PMAT
Prophase
Metaphase
Anaphase
Telophase
what occurs in prophase?
- chromosomes condense (shorten thicken) and become visible
- nucleolus disappears
- spindle develops
- nuclear envelope disintegrates
what is a spindle?
protein microtubules
what occurs in metaphase?
- chromosomes line up at the equator
what occurs in anaphase?
- chromosomes split and chromatids separate
- spindles contracts and the chromatids are pulled to the opposite poles of the cell centromere first
what does the movement of chromatids rely on?
cell cytoskeleton and ATP
what occurs in telophase?
- spindle disintegrates
- nucleolus reforms
- nuclear envelope develops
after telophase cytokinesis occurs, what happens in cytokinesis?
the cell membrane constricts around the equator, forming two daughter cells that are genetically identical to the original cell
what does the term clones mean?
offspring are genetically identical to the original, parent organism
budding in yeast cells
- parent yeast cell swells on one side, forming a bud at the cell surface
- the nucleus divides by mitosis
- the nucleus (and cell organelles and cytoplasm) move into the swelling/bud
- cytokinesis occurs and the bud pinches off and separates from the plant cell, producing a new genetically identical yeast cell
differences in mitosis between animal cells and plant cells
ANIMAL
1. cells become rounded
2. occurs in most cells
3. centrioles form spindles
PLANT
1. no change in shape
2. only occurs in meristem
3. no centrioles (form from tubulin)
what is cancer?
uncontrolled cell division
what is a tumour?
an irregular mass of cells
definition of an oncogene?
any gene that could potentially cause cancer
what happens in stages of meiosis?
s phase= DNA is replicated so the mass of DNA doubles
meiosis i = the homologous pairs of a separate number of chromosomes half aswell as a mass of DNA
meosis ii= the sister chromatids seperate so each daughter cell has only one chromatid so mass of DNA halves again
why must the chromosome number be halved in meiosis?
at fertilisation it will restore the diploid number
meiosis i
prophase
- the chromosomes condense and become visible
- the chromosomes come together as homologous pair(a process called synapsis) each H is bivalent
- non-sister chromatids wrap round each other and attach at points called chiasmata
- they swap sections of chromatids with one another in a process called crossing over
- the nucleolus disappears and the nuclear envelope disintegrates
- centrioles move to opposite poles and spindle forms
what is each homologous pair called?
bivalent
what does crossing over do?
gives chromatids new combination of alleles
metaphase i
- bivalents line up at the equator of the cell randomly, attached to spindle fibres at their centromeres
- this allows independent assortment
what is independent assortment ?
process where the chromosomes move randomly to separate poles
with 23 pairs of chromosomes there are ..
2^23
anaphase i
- the homologous chromosomes in each bivalent are separated, spindle shortens, and chromosomes are pulled to opposite poles
- the centromeres do not divide
telophase i
- the nuclear envelope reforms around each set of haploid chromosomes
- there is a brief interphase and the chromosomes uncoil
the cell now divides by mitosis
meiosis ii
PROPHASE II
nuclear envelope breaks down and nucleolus disappears
chromosomes condense
spindles form
METAPHASE II
the chromosomes line up at equator and attach to spindles by centromere
independent assortment occurs because the chromatids of the chromosomes can face either pole - increases GENETIC VARIATION
ANAPHASE II
the centromeres split and the chromatids are pulled to opposite poles
TELOPHASE II
nuclear envelope and nucleoli reform and the spindle disintegrates
the chromosomes elongate and are no longer visible
CYTOKINESIS OCCURS
4 haploid, genetically different daughter cells
