Cells • Cells are the smallest living unit of life • Cells have a nucleus, cytoplasm, and plasma membrane • Cells make proteins • Cells have DNA in their nucleus • Cells divide to make new cells
Genes and Proteins • Proteins do the work of the cell: growth, maintenance, response to the environment, reproduction, etc. • Proteins are chains of amino acids.
Genes and Proteins • The sequence of amino acids in each protein is coded in the DNA as a specific sequence of A, C, G and T bases: a gene. • Each gene codes for a different protein.
Genes and Proteins • All cells within an organism have the same genes. • What makes cells different from each other is that different genes are turned on and turned off in different cells.
Cell Division • The DNA must be copied and then divided exactly so that each cell gets an identical copy.
Cell Division • Two types of cell division • Mitosis • For growth and repair • Meiosis • For formation of gametes - sperm and egg
Cell Division All complex organisms originated from a single fertilized egg.
Cell Division Every cell in your body started here, through cell division the numbers are increased
Cell Division Cell then specialise and change into their various roles
Mitosis • Mitosis is the process by which new body cell are produced for: • Growth • Replacing damaged or old cells. This is a complex process requiring different stages
Parent cell Chromosomes are copied & double in number Chromosomes now split 2 daughter cells identical to original
Mitosis • All daughter cells contain the same genetic information from the original parent cell from which it was copied. • Every different type cell in your body contains the same genes, but only some act to make the cells specialize – e.g. into nerve or muscle tissue.
Mitosis – bone cell slides 2 1 Parent cell Chromosomes copied 4 3 5 2 daughter cells Copies separating
Animated Mitosis Cycle • Interphase • Prophase • Metaphase • Anaphase • Telophase & Cytokinesis http://www.cellsalive.com/mitosis.htm
Interphaseoccurs before mitosis begins • Chromosomes are copied(# doubles) • Centrioles replicate Nucleus CELL MEMBRANE Cytoplasm
Interphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Early Prophase • Chromosomes appear as threadlike coils (chromatin) during interphase • At the start of prophase, (early prophase), chromatin condenses and coils into chromosomes. CELL MEMBRANE Nucleus Cytoplasm
Prophase 1st and Longest step in Mitosis • Mitosis begins (cell begins to divide) • Centrioles(or poles) begin to move to opposite ends of the cell. • Asters are seen Centrioles Sister chromatids Spindle fibers
Prophase • Chromosomes are condensed into sister Chromotidsheld together by a button-like body called a centromere • Nucleolidissappear • Spindle fibersform between the poles. Centrioles Sister chromatids Spindle fibers
Prophase Plant Cell Animal Cell Spindle fibers Centrioles Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Metaphase 2nd step in Mitosis • Chromatids(or pairs of chromosomes) attach to the spindle fibers. • Chromosomes cluster at the middle of the cells, with their centromeres aligned at the exact center, called the metaphaseplate Centrioles Spindle fibers
Metaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Anaphase3rd and shortest step in Mitosis • Chromatids(or pairs of chromosomes) separate and begin to move to opposite ends of the cell. • Cells elongate. Chromosomes look V-shaped Centrioles Spindle fibers
Anaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Telophase4th step in Mitosis • Two new nuclei form, nuclear envelope forms from rough ER • Chromosomes uncoil and appear as chromatin (threads rather than rods). • Spindle dissappears. Mitosis ends. Nuclei Nuclei Chromatin
Telophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Cytokinesis • Cytokinesis begins during late anaphase and continues through and beyond telephase • A contractile ring of microfilaments forms at the cleavagefurrow and squeezes cells apart
Cytokinesis • Cell membrane moves inward to create two daughter cells – each with its own nucleuswith identical chromosomes.
Mitosis • Cells divide by mitosis to make identical daughter cells
Cell Division • Mitosis – Division of the nucleus • Cytokinesis – Division of the cytoplasm
Summary of Mitosis • Prophase: • Chromosomes condense • Nuclear envelope disappears • Centriolesmove to opposite sides of the cell • Spindle forms and attaches to centromereson the chromosomes
Summary of Mitosis • Metaphase • Chromosomes lined up on equator of spindle • Centriolesat opposite ends of cell
Summary of Mitosis • Anaphase • Centromeres divide: each 2-chromatid chromosome becomes two 1-chromatid chromosomes • Chromosomes pulled to opposite poles by the spindle
Summary of Mitosis • Telophase • Chromosomes de-condense into chromatin • Nuclear envelope reappears • Cytokinesis: the cytoplasm is divided into 2 cells
From Cell to Human …. Part 2
Meiosis Video • http://www.youtube.com/watch?v=mKWxeMMFTEU
Meiosis • There is a special type of cell division to make a sperm or egg • To make gametes, cells must undergo meiosis
Why do we need meiosis? • Meiosis is necessary to halve the number of chromosomes going into the sex cells • Why halve the chromosomes in gametes?
Why do we need meiosis? At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents
Meiosis • The form of cell divisionby which gametes, with half the number of chromosomes,are produced. • Diploid (2n) haploid (n) • Meiosis is sexual reproduction. • Two divisions (meiosis I and meiosis II).