The Cell Cycle

G1 phase

1st phase in interphase-period before DNA replication-cell grows in size and receives internal and external signals to decide if it should divide-if positive, cell enters S phase to continue cell division(no turning back after this!)-if negative, cell will not divide-prevents too much cell division from happening

tetrads

2 homologous chromosomes join-2 pairs of sister chromatid line up side by side and joined by proteins-

2.)(M) Mitotic phase & 1.)Interphase

2 stages of cell cycle

S phase

2nd phase in interphase-replication of DNA-chromosomes duplicate themselves-sister chromatids produced

G1 to S phase: determines if DNA is intact and suitable for replication-G2 to M phase: determines if DNA was accurately replicating-Metaphase to Anaphase: determines if chromosomes are attached to spindle microtubules, aligned properly along cell equator

3 checkpoints of cell cycle (mitosis stops if checkpoint determines problem)

G2 phase

3rd phase in interphase-period after DNA replication-continued cell growth-cell division occurs after this phase(mitosis and meiosos)

genome

All the genetic information in an organism; all of an organism's chromosomes.

prophase 2

BEGINNING OF MEIOSIS 2-chromosomes recondense-spindle microtubules form-attach to kinetochore-

plant cell wall is too stiff for normal cytokinesis-carbohydrate filled vesicles line along equator of cell and fuse to form cell plate-cell plate merges with plasma membrane and form cell wall between daughter cells

How does cytokinesis in animal cells differ from cytokinesis in plant cells?

cytokinesis 2

MEIOSIS 2-4 haploid daughter cells-each daughter cell genetically different-each daughter cell contains 1/2 of parent DNA-1/2 original # of chromosomes(unduplicated)

anaphase 2

MEIOSIS 2-chromatids separate-independent chromatids(unduplicated chromosomes) move toward opposite poles-1 chromatid from each chromosome at each pole

metaphase 2

MEIOSIS 2-chromosomes line up along equator-chromatids face opposite poles

telophase 2

MEIOSIS 2-spindle microtubules disintegrate-nuclear envelopes reform at poles-nucleoli reappear

cytokinesis 1

MEIOSIS-cell divides into 2 haploid cells-chromosomes are duplicated-1 duplicated chromosome(2 chromatids)

telophase 1

MEIOSIS-chromosomes arrive at poles and spindle microtubules disappear-each pole has haploid set, but each chromosome has two chromatids-nuclear envelope may reform

anaphase 1

MEIOSIS-homologous chromosomes in a tetrad separate from each other and move toward opposite poles-1 chromosome of each homologous pair at each pole

prophase 1

MEIOSIS-post crossing over-tetrads detach from nuclear envelope-nucleoli and nuclear envelope disappear-centrioles move towards poles-spindle microtubules form and attach to chromatid pairs of tetrads at kinetochores

Interphase

MEIOSIS-same to interphase before-G1-->S phase-->G2-duplication of chromosomes-->sister chromatids-sister chromatids attached at centromere

metaphase 1

MEIOSIS-tetrads line up along equator of cell-1 homologue per tetrad faces pole-random orientation--->genetic variation-spindle microtubules attach at kinetochore

Prophase

MITOSIS-Early Prophase: chromosomes condense and become visible-spindle microtubules form between centrioles-centrioles move towards poles of cell-Late Prophase: nucleolus and nuclear envelope disappear-centrioles at opposites poles-spindle microtubules capture chromosomes at kinetochore of centromere-polar microtubules elongate the cell

Metaphase

MITOSIS-microtubules lengthen and shorten-chromosomes line up on equator of the cell(metaphase plate)-sister chromatids face toward opposite poles

Cytokinesis

MITOSIS-often occurs during telophase-division of cytoplasm between daughter cells-plasma membrane pinches cell into 2 daughter cells

Anaphase

MITOSIS-sister chromatids separate-individual chromosomes move toward poles-each pole gets 1 copy of each parental chromosomes-cell continues to elongate

Telophase

MITOSIS-spindle microtubules breakdown-nuclear envelope forms around chromosomes at each pole-nucleoli appear-chromatins uncoil

centrioles

a type of tubulin protein responsible for formation of the mitotic spindle-move towards poles of cell

kinetochore

assemblies of proteins that function in attaching the chromosomes to mitotic spindle

differentiated cells capable of dividing

can only divide for specific part (EX: liver cells-divide to become more liver cells only)

stem cells

capable of dividing and differentiating-self renewable(divide for entire life of organism)-generate cells and tissues for transplant--research-differentiate into variety of cell types (EX: embryonic stem cells, somatic stem cells, ____ cells in bone marrow--->blood cells)

binary fission

cell division in bacteria-parent organism divides & makes 2 genetically identical daughter cells-occurs rapidly 1.)chromosomes replication 2.)membrane elongates until cell is twice its normal size 3.)plasma membrane pinches inward 4.)cell wall forms between two daughter cells

important note

cell division is required for organism reproduction

interphase

cell growth and copying of chromosomes in preparation for cell division(before mitosis and meiosis)-about 90% of cell cycle-divided into sub phases G1, S phase, and G2

cell theory

cells arise from preexisting cells

chromosomes

compacted chromatin-contain 1000 genes

chromatin

complex of proteins and DNA

haploid cells

contain 1 chromosome of each type-sex cells-1/2 set of chromosomes until fertilization occurs-#N-gamete (sex) cells-cells with single chromosome-created by meiosis

diploid cells

contain homologous chromosome pairs-majority of cells EXCEPT sex cells-complete set of chromosomes present-#2N-somatic (body) cells-cells with paired chromosomes-created by mitosis

somatic cells

diploid # 46-22 pairs of homologous chromosomes(also called autosomes)-pairs similar in appearance and size-1 pair of sex chromosomes

46 chromosomes

how many chromosomes are found in a human somatic cell during G2?

22 homologous pairs of chromosomes

how many homologous pairs of chromosomes are found in a human somatic (body) cell during G2?

92 chromatid

how many sister chromatids are found in a human somatic cell nucleus during G2?

permanently differentiated cells

incapable of dividing after differentiation (EX: brain and heart cells)

chromosomes in humans

individually you have 46 chromosomes-22 sets are homologous chromosomes(which means 2 XX make 1 set of homologous chromosomes)(diploid pairs)-1 set is your sex chromosome(23)--22+23=46

centromere

located at center of chromosome-attatchment site for microtubules for chromosome movement -control activity of chromosomes

telomere

located at ends of chromosome-essential for chromosomes stability

Mitotic (M) Phase

mitosis/meiosis/cytokinesis

crossing over of DNA

mutual exchange of DNA segments-occurs between chromatids at chiasmata-result: genetic variation

sexual reproduction

offspring arise from 2 parents-fusion of gametes-each gamete contains half of the parents genetic info-fusion results in 1 complete set of genetic info-more complex but variation can occur

asexual reproduction

offspring arise from single parent-offspring are identical to parent-complete set of genetic info passed from parent to offspring (ex; bacteria)-simple but no variation -all prokaryotes and few eukaryotes(unicellular)-involve period of growth and DNA replication-divide in binary fission

Meiosis

prerequisite for sexual reproduction-occurs in sex cells that produce gametes ((testes(sperm)and ovaries(egg))-end with 4 haploid daughter cells-each contains 1/2 of parents genetic info-NOT genetically identical to each other or parent-consits of: interphase, meiosis (nuclear division), cytokinesis

mitosis

produces 2 daughter cells genetically identical to each other and parent cell-each contains 1 copy of parent chromosomes-division of genetic information between 2 daughter cells-occurs after interphase-4 phases: Prophase, Metaphase, Anaphase, Telophase

microtubules

protein complexes responsible for moving chromosome during cell division

cell cycle

repeating pattern of growth, division, and possible differentiation

gametes

sex cells-sperm and egg-haloid # 23---22 unpaired chromosomes + 1 sex chromosome-become diploid after fertilization

locus

specific location on chromosome

chiasmata

visible linkage site between sister chromatids-2 or 3 may form between homologues

crossing over-random alignment of homologous chromosomes at metaphase plate during metaphase 1-sexual reproduction-mutation in genes

what are some events that can lead to genetic variation?

sister chromatids are identical to each other-homologous chromosomes are not identical

what are the differences between sister chromatids vs. homologous chromosomes?