IB Biology HL D2

cell and nuclear division

cytokinesis

division of cytoplasm of mother cell to form two daughter cells

occurs differently in plant and animal cells

cytokinesis in animal cells

1. cleavage furrow is created by a ring of proteins (actin and myosin)

2. cleavage furrow reaches center

3. cells pinch apart into two daughter cells

cytokinesis in plant cells

1. vesicles move to equator

2. vesicles fuse and form tubular structures

3. tubular structures form two plasma membranes

4. cellulose brought to middle to form cell wall

5. cell wall formed

unequal cytokinesis

yeast budding - outgrowth from mother cell that splits away

oogenesis - 1 large ovum and 3 polar bodies. ensures ova being fertilized has most nutrients and chance of survival

why do cells divide (3)

growth

tissue repair

cell replacement

where do cells come from (2)

all cells from from pre-existing cells

traced back to LUCA

mitosis vs meiosis (4)

genetics, result, function, reproduction

mitosis

continuity

results in 2 diploid cells

ensures every cell has all genes

asexual reproduction

meiosis

variation

results in 4 haploid cells

produces gametes

sexual reproduction

what happens before meiosis and mitosis

DNA replication (creation of identical chromosomes)

chromosomes supercoil and fold before cell division

sister chromatids

held together by cohesin

identical sequences of DNA

movement of chromosomes in mitosis and meiosis (3)

moved by microtubules

subunits moved by kinetochore protein (like molecular motor) that cause microtubules to shorten

sister chromatids will separate to opposite poles

tRNA molecules (2)

carry specific amino acid that corresponds to anticodon loop

3 anticodon bases that bind to complementary codon

ribosomes

large and small subunit

APE sites

phases of mitosis (4)

prophase, metaphase, anaphase, telophase

nondisjunction

when chromosomes don’t separate properly

gamete typically dies

trisomy

nondisjunction that results in extra chromosome

typically fatal

down syndrome

how does meiosis increase genetic variation

crossing over

random orientation

random orientation

random orientation of bivalents (two homologous pairs) in metaphase I

how microtubules arrange homologous chromosomes at equator

each homolog attatch to seperate microtubules

crossing over (4)

happens in prophase I

exchange of DNA segments between non-sister chromatids at the same locus

occurs in random loci

creates new combinations of alleles

synapsis

process of homologs being paired into bivalents

chiasmata

X shape seen in late prophase of DNA

crossing over mechanism

homologs complete synapsis and pair into bivalents

part of DNA segment is cut off at same locus and reattached to opposite sister chromatid

meiosis phases

prophase I, metaphase I, anaphase I, telophase I

prophase II, metaphase II, anaphase II, telophase II

interphase

G1 - normal cell function. respiration, protein synthesis, growth

S - DNA replication, sister chromatids held together by cohesin

G2 - cell activity to prepare for cell division

cyclin

protein that initiates different parts of cell cycle

A, B, D, E

cyclin D

triggers cells to fmove from G1 to S

cyclin E

prepares cell for DNA replication in S phase

cyclin A

activates DNA replication inside nucleus in S phase

cyclin B

promotes assembly of miotic spindle fibres in cytoplasm to prepare for cell division

genotype

combinations of alleles of a gene

phenotype

physical trait of expressed genotype

epigenetics

the relationship between the environment and genetics and how it may change expression of genes

differentiation

process of unspecialized cells taking on specialized characteristics to reach specialized functions and structures

transcriptome

all information encoded in mRNA

proteome

entire set of proteins in cells

epigenetic tags

chemical modification to chromatin that affects gene expression

methylation

methylation

turns off gene by methylating cytosine bases in promotor

or binds to histone proteins that coil DNA. loosens chromatin = more gene expression vice versa

epigenome

sum off all epigenetic tags in an organism

99% removed in DNA for gametes

epigenetics in identical (monozygotic) twins

identical epigenetic tags from parent cells

as they grow, will respond differently to tags

gene expression during transcription

transcription factor binds in promoter to help RNA polymerase find TATA box

repressor proteins bind to silencers sequences to decrease rate of transcription

activator proteins bind to enhancer sequences to increase rate of transcription

gene expression during translation

controlled by length of poly A tail

depends on rate that exonucleases can degrade poly A tail

roles of ligands and receptors in gene expression (transcription)

so cells can respond to environmental stimuli