Limits to cell growth Surface area to volume ratio

Cell Division About 2 trillion cells are produced every day by an adult human body. This is about to about 25 million per second!! Cells undergo growth, development repair and reproduction. The division of somatic cells in eukaryotes is Mitosis (asexual reproduction).. Ex. skin cells, heart cells, blood cells.

A second type of reproduction takes place in prokaryotes. Bacterial cells called binary fission. There are two stages in binary fission: first DNA is copied, second the cell divides, resulting in two identical cells also known as clones. The third type is sexual reproduction of gametes (sperm and egg), this is known as Meiosis.

Chromosomes Chromosomes are located in the _____ of the cell. Each chromosome is made up of segments called genes. Genes produce proteins that determine characteristics and functions of the cell.

Structure of a chromosome

Homologous Chromosomes Humans have 46 chromosomes 23 from each parent These are called homologous chromosomes because: –They are the same length –Have the centromere in the same location –Carry genes for the same trait Same trait different characteristics

Sex cells Every cell contains a full set of chromosomes Only half of these chromosomes are passed on to the offspring Special cells called gametes (sex cells) are produced containing ½ of the original number of chromosomes. –Example: a human has 46 chromosomes in a normal cell. A gamete or sex cell only has 23 chromosomes

Haploid and diploid cells Every species has a different number of chromosomes see table 1 p.121 The letter n is used to represent the number of chromosomes in general terms A gamete with half the number of chromosomes is called haploid and is represented by n

When two haploid cells come together during fertilization a diploid cell is formed and is represented by 2n page 120 fig.3 A zygote is a fertilized egg the first cell of a new individual

Questions Where in the cell are chromosomes located? Each chromosome has segments called? What product do genes code for? What are homologous chromosomes? What is the name given to sex cells? How many chromosomes do (humans) sex cells have?

Chromosomes Continued…. You have 23 pairs of homologous chromosomes. 22 of the pairs are autosomes not involved with determining sex of an individual. the 23 rd pair does determine the sex of an individual. In humans XX is female and XY is male

Karyotype A human has 46 chromosomes and each chromosome has thousands of genes. Each gene plays an important role in growth and function. A karyotype is a picture (see p. 122) of the chromosomes in a dividing cell arranged by size. An extra chromosome 21 means the person has trisomy 21 also known as Down Syndro me.

Karyotype

Mutations Are changes in chromosome structure. There are four types of mutations: 1.Deletion - a piece breaks off and is lost. 2.Duplication - A piece is repeated. 3.Inversion - A piece breaks off and reattaches in the wrong order. 4.Translocation - Apiece attaches to a different chromosome.

Check Point Analysis Describe how a cell might be affected by each mutation if the cell were to receive a chromosome with that mutation?

Cell Cycle Regulates cell size and reproduction Each time a cell completes one cycle a new cell is formed three main stages of the cycle –interphase –Mitosis –Cytokinesis

Cell Cycle

Interphase Animal Cell Plant Cell Photographs from:

Interphase – substage 1 G1 (first stage) – cell growth and daily functions. – Nerve and muscle cells may not ever divide again. So they are suspended in G1 and if they die they are not replaced. –Major portion of cells life is G1

Interphase – substage 2 S (second stage) – Synthesis stage - DNA is replicated. –Chromosomes contain genetic material. Chromosomes are tightly coiled and are located in the nucleus. –Chromatin is the uncoiled form of a chromosome. The chromosome must uncoil and become chromatin before it is replicated.

Interphase – substage 3 G2 (third stage) – cell prepares for mitosis –Microtubules (hollow protein fibers) are formed –The nucleus prepares to divide –Cell makes sure it is ready for division

After interphase Mitosis and cytokinesis –Mitosis – cells nuclear material divides and seperates –Cytokinesis – the rest of the cell divides to form two separate daughter cells

Mitosis During mitosis the cell is replicated The DNA that was copied in the S phase of interphase is now separated equally during mitosis The two new cells are called daughter cells and are identical There are four stages –Prophase –Metaphase –Anaphase –Telophase

The cell between Interphase & Mitosis At the end of the G2 phase of interphase the cell has two copies of its DNA inside one nucleus Mitosis will separate those two copies so that the two new daughter cells have one set of DNA each

Prokaryotic vs. Eukaryotic cells Because eukaryotic cells have membrane bound organelles and a nucleus they must go through the cell cycle Prokaryotic cells are less complex and go through binary fission

Cell Division Check Point What is the purpose of cell division? How many cells are reproduced from each cell? Do cells reproduce throughout your entire life? What are the five stages of the cell cycle? What are the three phases of interphase?

Thursday, January 7, 2010 Do Now: The nerve cells in a human nervous system seldom undergo mitosis. Predict how well you think the body is able to repair damage to parts of the nervous system. Objective: Examine the events that take place in mitosis. Homework: Page 134 #1-7.

Prophase see p First the chromatin recoils to form chromosomes what look like X’s –Each ½ of the X is a sister chromatid (identical copies of the DNA) –The X is held together by a centromere The nuclear membrane & nucleolus dissolves Spindles begin to form between the two nuclei

Prophase Animal Cell Plant Cell Photographs from: Spindle fibers Centrioles

Metaphase Chromosomes line up (in center) along the equator. Spindle fibers connect to sister chromatids. Ensures that each daughter cell have accurate copies of the chromosome

Metaphase Animal Cell Plant Cell Photographs from:

Anaphase The chromatids are pulled apart as the microtubules begin to shorten. The microtubule is pulling on the centromere of each sister chromatid. Separation of the sister chromatids happens all at the same time. Now are chromosomes. At the end of the anaphase the sister chromatids are separated equally and are moving toward opposite sides or poles of the cell

Anaphase Animal Cell Plant Cell Photographs from:

Telophase A new nuclear membrane begins to forms around each set of chromatids and the nucleolus reappears in the nucleus on each side. The spindles disassemble and the microtubules are recycled to be used as part of the cells cytoskeleton. At the end of the Telophase the sister chromatids are separated equally and are on opposite sides or poles of the cell with a new nucleus and nucleolus.

Telophase Animal Cell Plant Cell Photographs from:

Cytokinesis Cytokinesis is the separation of the cytoplasm and the pinching in of the cell membrane. Ex. similar to the way draw sting pants tighten when you pull the string.

Cytokinesis

Animal Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Interphase

Plant Cells The plant cell has a cell wall. Plant cells do not undergo cytokinesis. The cell wall does not pinch in, instead a cell plate is formed between the two new cells. The plate will develop into a cell wall and separate the two cells.

Plants cell plate

Plant Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Interphase

REMEMBER! I Interphase P Prophase M Metaphase A Anaphase T Telophase C Cytokinesis IPMATC I

Cell Cycle 44

The Cell Cycle 45 - Cell Division 45

Cell cycle controls The normal cell cycle is controlled by cyclic proteins. As the cell cycle progresses the cell pauses to check and make sure there are no abnormalities before moving on. When this check point system fail cancer may ensue.

How abnormalities get through Because the cell cycle is so very complex there are many things that can go wrong When the cell misses an abnormality or does not respond to the cyclic proteins a condition called cancer can form Cancer is an uncontrolled cell cycle when cell begins to divide and doesn’t stop

Cancer cell karyotype

What causes cancer Weak organisms as well as healthy ones can get cancer Cancer is caused by mutations in sections of the DNA The mutations are often repaired but when they are not they can cause cancer The mutations in the DNA can be caused by environmental factors such as carcinogens – things that are known to cause cancer

The genetics of cancer Cancer is not the result of one DNA mutation Over a lifetime several changes in the DNA may occur possibly resulting in cancer – multi - hit. The possibility of cancer increases with age Offspring can inherit these changes leading to an increased risk of cancer

The death of a cell Apoptosis is when cells are programmed to die –Examples the cells between the fingers and toes of a developing child Leaves falling off trees in autumn Apoptosis can also protect an organism from defective or mutated cells

Stem cells Stem cells are cells that do not yet have a specialization Embryonic stem cells –The first 100 or so cells of an organism are stem cells –The stem cells, after forming the basis of the organism begin to specialize into tissues and organs Adult stem cells –Found sporadically throughout an organism and are used for repairs in that adult