Biology 30 16.1,16.2,16.3

Overall ( Somatic Cells )

• lives of somatic cells vary based on their type and their environment

Cell Cycle

2 Parts to the cell cycle:

• Maintenance

• Division - all new cells must function the same as the cells they came from

• DNA is found in each chromosome

  Eukaryote - nucleolus is where the chromosomes are located

Histones

• Highly organized arrangement of proteins

  DNA compacts this material, storing genetic material + intertwines around it forming chromatin > chromosome

Centromere

• pinched in region, where the genetic material in the form of chromatin condenses into chromosomes

Chromosomes

• Human SOMATIC cells = 46 chromosomes

  autosomes -organized into 22 pairs of homologous chromosomes

• 2 Sex Chromosomes ( X & Y ) - determines the sex/gender of an individual

  female (XX)

  male (XY)

  ( counted as a pair even though they are homologous )

• homologous chromosomes carry the same genes at the same location

not identical to each other, has different forms ( alleles )

Diploid

• cell that contains pairs of homologous chromosomes

46 chromosomes, 23 pairs/chromatids

• 2n = 46

Haploid

• cell that contains unpaired chromosomes

• n = 23

Polyploid

• sets of more than two homologous chromosomes

Karyotype

• particular set of chromosomes, prepared by collecting a cell sample and using chemicals go stop them in a cell cycle when chromosomes are most visible > stained to identify each individual chromosome

Stages of the Cell Cycle

2 main stages:

Growth & Division

Growth - most somatic cells life is spent here (interphase)

Interphase

• cells carry out regular metabolic functions and prepare for its next division

Three Phases:

• G1 = cells grow rapidly

• S = midway through interphases, cell’s DNA is copied > DNA chromatin is replicated to create a second identical set of DNA (sister chromatids)

• G2 = cells that have completed S-phase, will rebuild its reserves of energy for cell division

Cell Division

• Mitosis - division of genetic material + contents of the nucleus into two complete and separate sets

• Cytokinesis - division of cytoplasm into 2 functional cells + organelles into separate cells

together they form daughter cells with the same genetic material as the parent cell

Three important functions:

• Growth = enables organism to grow form single-celled zygote into a mature organism that may contain hundreds of trillions of cells

• Maintenance = produce new cells to replace worn out/dead cells

• Repair = regenerate damaged tissues

Mitosis

Prophase:

• Chromatin condenses into tightly packed chromosomes

• nuclear membrane breaks-down, releasing chromosomes into the cytoplasm —> nucleus disappears

• microtubules form spindle fibres

Metaphase ( Middle )

• spindle fibres guide the chromosomes to the equator ( middle )

• spindle fibres from opposite poles attach to the centromere of each chromosome > one sister chromatid faces one pole, other sister chromatid faces the opposite pole

Anaphase (Apart)

• each centromere splits apart —> sister chromatids separate from one another > spindle fibres that link the centromeres to the pole, shorten = chromosomes are pulled to opposite poles

• microtubules in other spindle fibres forces the poles of the cell away from one another

• complete diploid set of chromosomes has been gathered at each pole of the elongated cell

Telophase

• chromatids reaches the opposite pole of the cell

• chromatids begin to unwind into longer less visible strands of chromatin

• spindle fibres breakdown

• nuclear membrane forms around each new set of chromosomes + nucleus forms within each new nucleus

Cytokinesis

animal cells > indentation forms in the cell membrane along the equator

• deepens until the cell is pinched into two

cytoplasm & organelles divide equally between both cells

plant cells > does not have centrioles, but still forms spindle apparatus

does not pinch during cytokinesis, creates a cell plate between the two daughter nuclei + reinforced to create a new cell wall

Regulation of the cell cycle

• Protein interactions = start/stop signal in cell division

  external factors such as particular hormones, availability of nutrients + contact with other cells plays a role

  • anything that interferes with regulatory signals = cell cycle proceeds at an uncontrollable rate

• rapid cell divisions = cancer

  one cancerous cell moves quickly from one cell division to another

  mass of non-functioning cells = tumour

Meiosis notes

• somatic cells reproduce = must have the same information + number of chromosomes as the parent cell

• during sexual reproduction, gamete from paternal + maternal = zygote

• gametes MUST contain HALF = haploid the number of chromosomes as the somatic cells of the organism

• sperm = testes

• egg = ovaries

  in total 23 chromosomes

Meiosis (ACTUAL PROCESS)

interphase - GERM cells produced through G&S

germ cells contain duplicated chromosomes

sister chromatids held together at centromere

PROPHASE 1:

• each pair of homologous ( not identical ) chromosomes align side by side = synapsis

  contains the same genes —> different alleles of these genes

• at synapsis, homologous chromosomes pair up > tetrads = 4 chromatids

  in the middle of the tetrad, two homologous but non-identical chromatids ( non-sister chromatids ) lie side by side

  • Crossing over !!

METAPHASE 1

• spindle fibre attaches to the centromere of each chromsome

• spindle fibre from one pole attaches to one pair of sister chromatids in the tetrad

• opposite pole attaches to the other pair of sister chromatids

• spindle fibre guides each tetrad to the equator of the cell

• does not line up in a single file line —> lines up as homologous place ( placed on one side of the equator )

ANAPHASE 1

• spindle fibres shorten, causing the homologous chromosomes to separate from one another

  moves to opposite sides of the pole

• sister chromatids still together —> single chromosome from each homologous pair moves to each pole of the cell

TELOPHASE 1

• some cells move directly from anaphase 1 to meiosis 2

• homologous chromosomes begin to uncoil —> spindle fibre disappears —> cytoplasm dividided

• nuclear membrane forms around each group of homologous chromosomes —> 2 cells are formed

• each of these new cells contains one set of sister chromatids = haploid

• no chromosome replication (0 interphase)

  • MITOSIS ETC

Reduction

• form of cell division that produces daughter cells with fewer chromosomes than the parent cells

Recombination

• products of meiosis that has different gene combinations

Sources of Genetic Recombination

• creation of gametes that carry different combinations of maternal + paternal chromosome

  exchange of genetic material

Independent Assortment

• during metaphase 1, arranged homologous pairs along the equator

  each pair of maternal + paternal chromosomes fade opposite poles, independent from each pair

Crossing Over

• lined up side by side during synapsis, non-sister chromatids exchange pieces of chromosomes

  can contain genes of both paternal and maternal

Non-disjunction

• chromosomes/chromatids do not separate as they should during meiosis

occurs in anaphase 1 and 2 meiosis

• Anaphase 1, homologous chromosome pairs do not separate in opposite poles, pulled to one pole

• Same for Anaphase 2, except its the sister chromatids

monosomy - when one chromosome is lost

gametes is missing one chromosome pair .. can lead to trisomy + turner syndrome