THE CELL CYCLE

THE CYCLE OF LIFE

Multicellular

You

Mitosis Meiosis

Unicellular You Unicellular Offspring

Cells must be smallAs cells grow bigger, problems developDNA Overload

Same amount of DNA must serve larger and larger areas

Surface Area/Volume RatioCytoplasm increases faster than cell membrane

Cell can’t exchange enough materialMaterial can’t reach center fast enough

WHY MUST CELLS DIVIDE?

SURFACE AREA/ VOLUME RATIOS

Surface Area (cube) = 6 x width2

Volume (cube) = width3

Surface Area/ Volume

COMPARING ORGANISMS

Unicellular Single cell will go through

cycle When cell gets too large,

it will divide Produces two new cell,

each one is its own organism

Form of asexual reproduction called binary fission

Each “offspring” is identical to the parent cell

Multicellular Beginning Cell- Zygote Cell(s) go through cell

cycle to form parts of organism

Cell division continues through development, growth, repair, and wear and tear

Each division creates 2 new cells identical to the parent cell

In some species, can be used for asexual reproduction such as budding and fragmentation

DNA REVIEW

Chromatin- Form of DNA during interphase

Chromosome Form of DNA during cell division

Centromere center point holding two sister chromatids together

Sister chromatids two copies of a chromosome held together by a centromere

Diploid (2n)Cells have 2 sets of chromosomes one inherited from mom and one

from dad

Found in somatic cells (all cells except sex cells)

Different number in different organisms Humans diploid # is 46

Homologous chromosomes- name of the 2 alike chromosomes from each set

DIPLOID

Haploid (n)Cells have 1 set of chromosomes

Found in gametes (sex cells)

Diploid # / 2 Human # is 23 (46 / 2)

When fertilization occurs, the organisms will have the diploid number again

HAPLOID

All cells in a multicellular organism except sex cellsBeginning cell- zygote (fertilized egg)

Totipotent- able to divide and create all the cell types needed in the body

Starts dividing to form early embryo (at 5 days is called a blastocyst) Pluripotent- able to divide and create many of the cell types

needed in the bodyContinues to divide to form the all the structuresAdult stem cells- found in various parts of the body

Multipotent- able to divide and create some of the cell types needed in the body

SOMATIC CELLS

Also called cell differentiation

Many different cell types Each has identical copies of DNA

Each type has a unique shape and function

CELL SPECIALIZATION

THE CELL CYCLE

INTERPHASE

INTERPHASE

Gap phase

Cell grows and carries out normal functions

G1

S PHASE

Gap phase

Cell grows and carries out normal functions

Other organelles replicate

G2

Some cells will never leave interphase or will stay in interphase for a very long time

Phase looks like G1These cells will not divide

G0

CELL DIVISION

Division of the nucleus of somatic cellsOne division with 4 phasesCell divides into two identical daughter cellsCells start diploid and end diploid

MITOSIS

PROPHASE

PROMETAPHASE

METAPHASE

ANAPHASE

TELOPHASE

CYTOKINESIS

ANIMAL VS PLANT CYTOKINESIS

AnimalCell membrane pinches together to form two cells

PlantCell plate forms Will become cell wall to form two new cells

External ControlsGrowth Factors and Hormones- stimulate cell division

Crowding- inhibits cell divisionInternal Controls

Cyclins- proteins whose levels rise and fall during the cell cycle; must reach a certain amount and interact with kinases to create cell division

Checkpoints- check that cell cycle is proceeding correctly S phase- checks if all DNA has been copied correctly Metaphase- checks if all chromosomes are on spindle

fiber

CONTROLLING CELL DIVISION

Uncontrolled cell divisionUsually results from mutations to

Oncogenes- accelerate the cell cycle Genes that stop the cell cycle

p53 gene- normally stops cell division from occurring until all chromosomes are replicated

Cells are undifferentiated and don’t do their job

Benign tumors- stay clustered togetherMalignant spread into other area creating problems (metastisize)

CANCER

Occurs in Unicellular prokaryotes Unicellular eukaryotes Some multicellular eukaryotes

Done by mitosis or processes similar to mitosisExamples

Binary fission Budding Fragmentation

ASEXUAL REPRODUCTION

Combines genetic information from two parentsCreates a unique offspringParents create gametes (sex cells) using meiosis

In humans, egg and sperm

SEXUAL REPRODUCTION

MEIOSIS

Meiosis Occurs in games (sex cells) 2 divisions with 4 phases each (8 phases total) creating 4 unique

cells Cells start out diploid and end haploid

CHARACTERISTICS

PROPHASE I

PROMETAPHASE I

METAPHASE I

ANAPHASE I

TELOPHASE I

CYTOKINESIS I

Similar to mitosisTwo haploid cells created by Meiosis I both divideCreates four haploid cells

MEIOSIS II

Formation of spermStarts at pubertyForms 4 sperm during each meiosisMen will make 5 to 200 million sperm/day

SPERMATOGENESIS

Formation of the eggMeiosis starts inside the womb,

continues is some during every cycle after puberty

1 egg and 3 polar bodies created after every meiosis

Egg must contain lots of cytoplasm to support the developing embryo after fertilization

OOGENESIS