Cell Reproduction Prokaryotes Bacteria Eukaryotes Plants animals Prokaryotes

Cell Reproduction Ø Ø Prokaryotes Bacteria Eukaryotes Plants & animals

Prokaryotes Ø Lack a nucleus Ø Have a single chromosome Ø Reproduce by binary fission Ø Include bacteria

Steps in Binary Fission Used by bacteria Ø Cells increase their cell mass slightly Ø the single, circular bacterial chromosome is replicated Ø Each cell divides into 2 daughter cells Ø

4

Binary Fission of Bacterial Cell

E. Coli Dividing by Binary Fission

Eukaryotes Contain a nucleus & membrane bound organelles Ø Asexually reproduce cells by mitosis Ø Begins with 1 cells, ends with two cells that are genetically identical to each other and genetically identical to the original cell Ø Occurs in somatic cells Ø Since a human somatic cell has 46 chromosomes (23 pairs) how many chromosomes will a cell produced by mitosis have? Ø

Cell Cycle l The cycle from the beginning of the one cell until the time that one cell divides into two cells l Mitosis is division of the nucleus Cytokinesis is division of cytoplasm and organelles Often the whole cell cycle is called mitosis, although this is not technically accurate

Purpose of Mitosis New cells for – Growth – Replacement (healing)

Cytokinesis Ø Occurs after chromosomes separate Ø Forms two, identical daughter cells

Cytokinesis Cell Plate Forming in Plant Cells

What is DNA like during cell division? DNA is always made of nucleotides with phosphate and sugar and nitrogenous bases, but what is the difference between DNA, genes, and chromosomes?

Chromosome, DNA, Gene demonstration

l Chromosome- a DNA helix that is supercoiled, compacted, and organized around proteins; they appear as mitosis begins and uncoil into DNA and protein during l Gene- a section of DNA that codes for a particular protein l Chromatin- DNA and its associated proteins that are not coiled and compacted; form that DNA maintains during interphase l DNA must be unwound to be able to be transcribed much like thread must be unwound to be used.

Details of Interphase

Cell Cycle Ø Interphase Ø G 1 Phase Ø S Phase Ø G 2 Phase Mitosis -M Phase Ø Cytokinesis Ø

Interphase – Resting Stage Ø Ø Ø Cells carrying on normal activities Chromosomes aren’t visible, instead they are in the form of chromatin – a complex of protein and DNA Cell metabolism is occurring Centrioles (microtubule-organizing centers) replicate and one centriole moves to each pole. Some sources make it the first stage of mitosis, some say it occurs before mitosis

Interphase - G 1 Ø First growth stage Ø Cell increases in size Ø Cell prepares to copy its DNA through the process of _______ replication

Interphase – Synthesis Ø Replication - Copying of all of DNA’s instructions Ø Chromosomes duplicated

Eukaryotic Chromosomes must be replicated before cell division. -Replicated chromsomes are connected to each other at their centromeres -sister chromatids: 2 copies of the chromosome within the replicated chromosome 20

21

What are Homologous Chromosomes? • In body cells, chromosomes occur as pairs. • Each set of chromosomes is a homologous pair; each member is a homologous chromosome or homologue. • One member of each homologous pair is inherited from the male parent, the other member from the female parent. • look alike, have the same length and centromere position, and have a similar banding pattern when stained. • A location on one homologue contains genes for the same trait that occurs at this locus on the other homologue, although the genes may code for different variations of that trait (alleles). www. treachercollins. co. uk (Mader 2007)

Interphase is composed of: G 1 (gap phase 1) – time of cell growth S phase – synthesis of DNA (DNA replication) - 2 sister chromatids are produced G 2 (gap phase 2) – chromosomes condense 23

Interphase Following S phase, the sister chromatids appear to share a centromere. In fact, the centromere has been replicated but the 2 centromeres are held together by cohesin proteins. Proteins of the kinetochore attached to the centromere. Microtubules attach to the kinetochore. 24

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Cohesin proteins Centromere region of chromosome Kinetochore microtubules Chromatid Kinetochore Metaphase chromosome 25

Interphase

27

Interphase - G 2 Ø Time between DNA synthesis & mitosis Ø Cell continues growing Ø Needed proteins produced

Eukaryotic Cell Cycle The eukaryotic cell cycle has 5 main phases: 1. G 1 (gap phase 1) 2. S (synthesis) interphase 3. G 2 (gap phase 2) 4. M (mitosis) 5. C (cytokinesis) The length of a complete cell cycle varies greatly among cell types. 29

Details of Mitosis and Cytokinesis

Mitosis - M Phase Ø Cell growth & protein production stop Ø Cell’s energy used to make 2 daughter cells Ø Called mitosis (nuclear division)

Stages of Mitosis Ø Prophase Ø Metaphase Ø Anaphase Ø Telophase

Cells Undergoing Mitosis

Steps in Prophase Ø DNA coils tightly & becomes visible as chromosomes Ø Nuclear membrane disappears Ø Nuceolus disappears Ø Centrioles migrate to poles Ø Spindle begins to form

Prophase

Eukaryotic Chromosome

Human Chromosomes

Steps in Metaphase Ø Spindle fibers from centrioles attach to each chromosome Ø Cell preparing to separate its chromosomes Ø Cell aligns its chromosomes in the middle of the cell

Metaphase

Steps in Anaphase Ø Cell chromosomes are separated Ø Spindle fibers shorten so chromosomes pulled to ends of cell

Mitotic Spindle

Anaphase

Steps in Telophase Ø Separation of chromosomes completed Ø Cell Plate forms (plants) Ø Cleavage furrow forms(animals) Ø Nucleus & nucleolus reform Ø Chromosomes uncoil

Telophase Plant Animal

Cytokinesis Ø Occurs after chromosomes separate Ø Separation of cytoplasm and formation of new cells each with one of the new nuclei Ø Forms two, identical daughter cells

Cytokinesis Cell Plate Forming in Plant Cells

Cleavage in Animal Cell

Eukaryotic Cell Cycle The eukaryotic cell cycle has 5 main phases: 1. G 1 (gap phase 1) 2. S (synthesis) interphase 3. G 2 (gap phase 2) 4. M (mitosis) 5. C (cytokinesis) The length of a complete cell cycle varies greatly among cell types. 48

Meiosis Creating Cells for Sexual Reproduction

Meiosis produces a haploid with only one set of chromosomes (reprented by N). Remember in somatic cells chromosomes come in pairs (2 N) , but meiosis produces haploid cells (gametes) that do not have pairs of chromosomes. They only have one set. Since human somatic cells have 46 (23 pair) of chromosomes, how many chromosomes are in a human gamete?

l Diploid Definitions Cells- (2 N)cells that have pairs of chromosomes. There are 2 of each chromosome in diploid cells. l Haploid Cells- (N)cells that have only one of each chromosome. Haploid cells are used for sexual reproduction.

Meiosis is divided into Meiosis I and Meiosis II

Meiosis I

Prophase I l Chromosomes are already copied l Centrioles separate l Nuclear membrane breaks down l Crossing over occurs here

Crossing Over Synapsis- Homologous Pairs line up = Tetrad l During synapsis the chromatids within a homologous pair may twist around each other and break off and attach to the other homologous pair = Crossing Over l l Results in exchange of genetic material between maternal and paternal chromosomes = genetic recombination