CELL REPRODUCTION

Chapter 8Miss ColabelliBiology CPA

CHROMOSOMES•Rod shaped structures made of DNA and proteins

•Chromosomes are visible in cells undergoing division

•Chromosomes are made by DNA coiling into tight structures

•Consist of two identical halves

CHROMOSOME STRUCTURE•Histones are proteins that DNA wraps around to make the chromosome shape

•Chromosomes are made of two sister chromatids• Identical to each other

CHROMOSOME STRUCTURE•Each chromosome is made of two “sister” chromatids

•Near center of the chromosome is the centromere

•Chromosomes are tightly coiled strings of DNA called chromatin

CHROMOSOME NUMBERS•There is a specific number of chromosomes in each organism•Ex: Humans have 46, chimpanzees have 48

•Humans have autosomes and sex chromosomes

•We have 2 sex chromosomes• Either X or Y

•We also have 44 autosomes •Which do not code for gender

CHROMOSOME NUMBERS•Every cell of an organism produced by sexual reproduction has two copies of each autosome•One copy from mom and one copy from dad

•The two copies of each pair is called homologous chromosomes•Same size and shape•Carry genes for the same traits

KARYOTYPE•A karyotype is a picture of one set of chromosomes•Shows you sex of organism•Shows your any chromosomal disorders

CHROMOSOME NUMBERS•A diploid cell contains 2 sets of each chromosome•Prefix di = 2•Abbreviated as 2n• n = number of chromosomes

•A haploid cell contains only 1 set of each chromosome•Half of the total number•Usually sex cells

CELL DIVISION IN PROKARYOTES

•Prokaryotes•No nucleus•No organelles•Ex: Bacteria

•Reproduction is very fast•Copy DNA•Split into two identical daughter cells

•Cell division is called binary fission

CELL DIVISION IN EUKARYOTES•Eukaryotes•Have a nucleus•Have organelles• Ex: Humans, plants

•Both nucleus and cytoplasm need to divide

•Process of making new cells is called mitosis• Makes two identical daughter cells

•Complex reproduction • Everything needs to be regulated!

•Much more complex process – about 18 hours!

CELL DIVISION AND REPRODUCTION•Asexual Reproduction•Produces identical offspring from a single parent•Used by many single-celled organisms • Ex: bacteria

•Occurs very quickly

•Sexual Reproduction•Produces genetically different offspring from two parents•Fusion of two parent cells•Creates haploid gametes (sex cells)

THE CELL CYCLE

•A repeating set of events in the life of a cell

•A cell splits to make 2 identical copies

•This occurs in 3 main stages

1. Interphase – growth

2. Mitosis – division of the nucleus

3. Cytokinesis – Splitting of the cytoplasm

INTERPHASE

•Cell growth•Majority of cell’s life span is spent in this phase•3 Part of Interphase: •G1, S, G2

G1 PHASE

•Gap 1 Phase•The cell is growing to mature size

S PHASE

•S = synthesis of DNA•DNA is copied so there is a set for each new cell

G2 PHASE

•Gap 2 Phase

•Cell grows again

•Replication of organelles

•Cell prepares for cell division

MITOSIS Cell Division

MITOSIS

•The part of a cell’s life cycle when the cell’s nucleus divides into 2 identical nuclei

•4 steps:•Prophase•Metaphase•Anaphase•Telophase

PROPHASE•Shortening and tight coiling of chromatin into chromosomes

•Nucleus breaks down and disappears

•Centrioles separate and move to opposite poles of the cell•Centrosomes in plant cells

•Centrioles shoot off spindle fibers

METAPHASE• Spindle fibers are

connected to centromere of chromosomes

• Spindle fibers move chromosomes

• Chromosomes line up at the equator of the cell• Chromosomes are in the

MIDDLE

ANAPHASE•Sister chromatids attach to the short spindle fibers

•Chromatids of each chromosome separate at the centromere•Chromosomes are pulled APART

•Spindle fibers shorten and bring the sister chromatids to opposite poles•After chromatids separate, they are called individual chromosomes

TELOPHASE•Chromatids become chromatin

•Spindle fibers disassemble

•Nuclear envelope forms around each set of chromatin

•Nucleolus reappears

CYTOKINESIS Division on the cytoplasm

CYTOKINESIS

•Once mitosis has finished!

•Last stage of cell cycle

•Process is when the cytoplasm splits apart

CYTOKINESIS IN PLANT CELLS•A cell plate forms between the two nuclei

•The cytoplasm divides

•A cell wall forms two daughter cells

CYTOKINESIS IN ANIMAL CELLS•Cell membrane pinches in at equator

•Cleavage furrow

CELLS IN VARIOUS STAGES OF THE CELL CYCLE

CONTROL OF CELL DIVISION•Checkpoints (Regulatory Proteins)• Repair enzymes fix any mutations

•G1 Checkpoint• Proteins check to see if cell will be able to divide• Check for cell size

•G2 Checkpoint• DNA repair enzymes check results of DNA replication during S phase

•Mitosis checkpoint• If all is correct, proteins will signal cell to exit mitosis• Cell will renter interphase after cytokinesis and start process over again

•If a cell does not meet requirements for checkpoints, the cell will be programmed to die Apoptosis is controlled cell death

Uncontrolled Mitosis

is cancer.

WHEN CONTROL IS LOST•Enzyme proteins are not functioning properly causing cell to reproduce out of control

•Could cause cancer

•Cancer cells do not respond to body’s regulators that control mechanisms

•A mass of cancer cells is called a tumor

COMPARE/CONTRAST