D2.1 Cell and nuclear division

4 purposes of cell division

• grow cells

• repair cells

• maintain cells

• limit cell size growth to maintain high SA:V for efficient material exchange and use

what does genetically identical mean

same # of chromosomes and genome

describe the loose DNA structure

chromatin

• present during interphase

• nucleosome structures

• allow enzymes to read DNA sequence for DNA transcription and replication

• not visible under microscope

describe condensed DNA structure

chromosome

• inc supercoiling makes easier to move, less tangling to minimise DNA damage

• present during mitosis

• visible under microscope

compare and contrast chromatin and chromosomes

• Chromatin is not visible under a microscope, chromosome is

• Chromatin is present during interphase, chromosome is present during mitosis

• Both are structures of DNA

outline events of interphase (3)

• inc cell size

• preexisitng organelles duplicate

• DNA replication within the nucleus (DNA as chromatin)

describe events of prophase (3)

1. DNA condenses into chromosomes

2. nuclear mem breaks down into vesicles

3. forming of spindle fibers

describe spindle fiber’s structure and function

• long fibrous proteins called microtubles + microtubules motor proteins at the base (controls microtubule length)

• move chromosoems around a cell by attaching to the centromere

describe events of metaphase (2)

1. spindle fibers bind to centromeres of chromosomes

2. chromosomes line up along the metaphase plate (moved by spindle fiber microtubules and motor proteins)

describe events of anaphase (2)

1. spindle fiber microtubules shorten via action of microtubule motor proteins

2. pull sister chromatids apart to opposite poles of the cell

describe events of telophase

1. nuclea rmem reforms 2 nuclei

2. chromosomes begin to decondens einto chromatin

3. spindle fibers begin to dissolve

define cytokinesis

the process of splitting cytoplasm of parent cell between 2 daughters

describe events of cytokinesis animal cell

1. contractile ring of motor protin (actin and myosin) pinch plasma mem inward, forming a cleavage furrow

2. splits the cytoplasm

   1. forms 2 separate daughter cells

describe events of cytokinesis plant cell

1. vesicles containing components of the plasma mem line up in the middle

2. fuse to form a cell plate to seprate into 2 daughter cells

describe what makes equal cytokinesis

1. same size daughter cells

2. equal cytoplasm

3. at least one mitochondria and any othe rorganelle duplicated during interphase

compare and contrast equal and unequal cytokinesis

• Equal size of cytoplasm versus unequal

• Equal split of organelles duplicated during interphase versus unequal

• Daughter cells have equal size versus unequal

• Both divided through cytokinesis

• Both has replicated DNA in each daughter cell (?)

explain unequal cytokinesis through two examples

budding in yeast

• a small bud (daughter) forms on the surface fo the yeast cell

• will detach after bud reaches a certain size

• a form fo asexual reproduction

• a process of cell growth and division

ooogenesis

• production of egg cells in the ovaries

• unequal division crates a large egg cell

• contain nutritional reserves and numerous organelles to support hte embryo in its first days

compare and contrast haploid and diploid

haploid has one set of chromosomes, diploid has two

haploid is produced through meiosis, diploid through mitosis

both are referring to # fo chromoomes in a cell’s nucleus

define homologous chromsomes

pair of chromosomes that are the same length, and share the same genes at the same location. work together to make genetic variation

define a chromosomes

a unti of condensed DNA.

not neccessarily replicated, can be a singular chromatid

compare and contrast mitosis and meiosis

• Mitosis has 1 nuclear division, meiosis has two

• Mitosis produces diploid, meiosis haploid

• Mitosis produces 2 cells, meiosis 4

• Both occurs after interphase

describe interphase I

same as mitosis

• inc cell size

• preexisitng organelles duplicate

• DNA replication within the nucleus (DNA as chromatin)

outline events of prophase I

1. DNA condenses into chromosomes

2. nuclear mem breaks down into vesicles

3. spindle fibers form

4. crossing over

   1. homologs align

      homologs pair up to form a tetrad/ bivalent

      forms a chiasmata

      DNA exchange between non-sister chromatids in a homolog pair

defien chiasmata

connection between non sister chromatids of a mologous pair where crossing over happens

purpose of crossing over is to

inc genetic variation

result in 2 pairs of non-identical sister chromatids

describe events of metaphse I (2)

• homologs line up at the metaphase plate

• spindle fibers bind on centromeres of chromosomes

describe events of anaphase I (2)

• spindle fibers shorten via the action of microtubule motor proteins

• homologs pulled apart of opposte poles, sister chromatids remainattached

describe events of telophase I and cytokinesis

• nulcear membrane reforms

• cytokinesis occurs to separate and for 2 haploid daughters

describe events in meiosis II

• same as mitosis

• spearates non identical sister chromatids

• produces new haploids, each chromosome has 1 chromatid

describe fertilisation

• fusion of 2 haploid gametes (egg and sperm) to restore the diploid number fo chromosomes in zygote

• repeated mitosis to grow amount

• random fertilization of gametes also leads to genetic diversity of offspring

describe genetic variation in crossing over

• sister chromatids are no longer identical

• homolog pairs do crossing over to exchange a certain DNA section

• each gamete will receive a diff combination of version of genes

describe genetic variation in random orientation

• tetrads orient randomly on the metaphase plate in metaphase I

• position of each homolog is random

• 50 50 chance, only two possible orientations for each homolog

• total number of possible combinations after meiosis I = 2²3 - > 8 billion

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