Cell Growth and Division Ch 8 Cell Size

Cell Growth and Division Ch. 8

Cell Size and Limitation • Cells come in a variety • What is diffusion? of sizes. – Diffusion limits cell size – DNA content limits size

Diffusion and DNA limit cell size because… • Cells rely on diffusion to carry on proper functions – Cells require a constant supply of glucose and oxygen – Cells must constantly get rid of waste. • DNA is found in all cells. – The larger the cell, the greater number of enzymes – DNA makes enzymes needed for the cell

Is bigger better? • Surface Area to Volume Ratio – As the cell size increases, its volume increases 2 x faster…. why is this a problem? Other ways to solve the problem • If cell size doubled, it would be an 8 fold increase in volume, but the surface area would only increase 4 fold. Therefore, there is not enough membrane for nutrients to flow through to keep the cell alive.

How do cells overcome this problem? • What do you think? – How will you get more membrane to compensate for the volume? • They divide into 2 cells allowing for twice as much membrane to be formed. 1. 7 a Cell growth and division are caused by complex interactions between the different kinds of molecules in the cell.

3 purposes of cell division 1. Growth • 1. 8 a All growth and development within a 2. Repair cell is a consequence 3. Reproduction of an increase in cell a. Asexual- offspring number, size and/or produced only by one products. parent. (bacteria) b. Sexual- produces offspring that have a combination of genetic material from two parent organisms.

Rate of Cell Division • The Pituitary gland secretes a growth hormone that tells cells when to divide and how much. If you lack this hormone, dwarfism may occur. 1. 7 b Molecules from different parts of the cells, such as hormones, can affect cell behavior.

Structure of eukaryotic chromosomes • Before cell division, each chromosome is replicated. • Each chromosome consists of 2 identical sister chromatids. • Each sister chromatid will separate from each other during cell division and go into its new cell. • Centromere region also called kinetochore. • When chromatin coils it becomes _______?

Chromosome Structure Histones are proteins that are wrapped up by DNA in the chromosome structure consisting of chromatin. This is then coiled many times within the chromosome.

1. 1 a All of the cells in your body come from a single cell that differentiates into many different cells, but they all essentially have the same genetic instructions. S IO ME MIT OSIS • 1. 11 All organisms begin their life cycles as a single cell, and in multicellular organisms, new generations of embryonic cells form by cell division.

1. 8 b Cells differentiate from each other because of gene expression and/or environmental influences. • Certain genes can be turned off or on at certain time. (Expresses or not expressed). • The environment can influence what cells are expressed or not. This also causes cells to differentiate.

The Cell Cycle • The cell cycle is the repeated sequence of cell growth (interphase) followed by cell division (mitosis) • 5 phases – – – Interphase Prophase Metaphase Anaphase Telophase Mitosis- process of nuclear division followed by cytoplasmic division. SOMATIC CELLS (body cells)

Mitosis vs. Meiosis • Mitosis – Somatic cells – 1 cell division – 2 daughter identical to parent • Meiosis – Gametes – 2 divisions – Daughter cells have half of genetic info as parent.

Interphase…a busy time (90% of cell cycle) • Cell activities during interphase: – – – – – Make ATP Repairing themselves Excreting wastes Making proteins Producing new organelles Duplicating DNA Chromatin duplicates Metabolism Cell growth in size • 3 phases: – G 1: normal growth phase (9 hours) – S: DNA is replicating (10 hours) – G 2: final growth in preparation for mitosis (2 hours)

Structure of the Chromosome • Each chromosome has two identical partssister chromatids that are held together by a centromere.

Chromosome number • Somatic Cells (body cells) of a particular species have the same number of chromosomes (humans have 46 or 23 pairs). • Chromosome number (n) tells how many of each type of chromosome is in the cell. – 1 n (haploid), 2 n (diploid)

Other structures used. . • Centrioles are a pair of cylindrical structures made of microtubules that are only found in animal cells and found just outside the nucleus. • Spindles are cagelike structures that are made of microtubules and used to separate sister chromatids. • Spindle fibers are the individual microtubules of the spindle.

Prophase- the first phase • Chromatin coils and becomes chromosomes. • The nucleus disappears. • Centrioles migrate to opposite poles of the cell. Made of microtubules. • The spindle forms and attaches to the centrioles and centromere. • Centrosome is where microtubules originate.

Metaphase- the • Chromosomes line up along the equator • Spindle fibers attach to the centromeres. nd 2 phase

Anaphase- the • Sister chromatids separate and centromeres split apart. rd 3 phase

Telophase- the • The “reverse” of prophase – Chromosomes uncoil to make chromatin – Spindle fibers disappear – Nucleus forms – Plasma membrane begins to from between 2 nuclei. th 4 phase

The final step • Cytokinesis- the division of the cytoplasm that results in two new daughter cells. • CELL CLEAVAGE- split in two • In plants, a cell plate forms across the equator, so the membrane doesn’t have to pinch in. • ** Centrioles are not found in plant cells during cell division. Mitosis in motion

The result • Each new daughter cell will have complete set of genetic material.

Apply Chromosome number • • Human somatic cell (46 or 23 pairs) G 1 S G 2 P M A T

Cell Cycle Regulators • Cyclins are proteins that regulate the timing of the cell cycle in eukaryotic cells. – Ex. Kinases end DNA replication. • Internal Regulators- proteins that respond to events inside the cell. • External Regulators- direct cells to speed up or slow down cell cycle. External or Internal? – Make sure cell doesn’t enter mitosis until all its chromosomes have been replicated. – Growth factors. – Prevents cell from entering anaphase until all of its chromosomes are attached to mitotic spindle.

Enzymes control the cell • Some control progression from one phase to another. • Come inhibit progression. • If too much or not enough is produced it can lead to cell death or cancer. • Genes control enzyme production. • Contact inhibition is another way the cell cycle is controlled. Cells normally stop dividing when they come into contact with each other. 1. 7 a Cell growth and division are caused by complex interactions between the different kinds of molecules in the cell.

Cancer. . A Mistake in the Cycle • Cancer is thought to be due to • changes in genes that make enzymes involved in the cell cycle. • Cells divide when they shouldn’t. • Cancer cells do not respond to the • signals that regulate the growth of most cells. • Oncogenes • Malignant vs. Benign • Neoplasm- abnormal masses of cells that have lost control over growth and cell division. Cancer cells can break away from a tumor (large mass) and travel through the blood to other areas in the body. Gene p 53 normally stops the cell cycle until all chromosomes have been replicated, but if there is a defect, growth is not controlled.

Characteristics of cancer 1. Grow and divide abnormally 2. Cell membrane is leaky, cytoskeleton is disorganized. 3. Cells have a weakened capacity for adhesion and may break away to move to other sites in the body (metastasis). 4. Cancer cells can have lethal effects.

Other causes of cancer • • Cigarette smoke Air and water pollution UV radiation Certain viruses – Cervical cancer -HPV – Mesothemioma – Liver cancer- Hep B • Some people may be born with genetic mistakes which may cause cancer. – Gene p 53. • Cancer is the 2 nd leading cause of death in the U. S. Heart disease is #1.

Stem Cells • Stem cells are unspecialized • Neurons are noncells that have the potential to replaceable. differentiate to become specialized in structure and • Embryonic stem cell function into a wide variety of research is very cell types. controversial because the • In early embryonic development, cells are taken from a stem cells produce every type of human embryo. tissue in the body. • Transplants fail- different • Stem cells in bone marrow can genetic info. make more than a dozen types of blood cells.

3 kinds of stem cells 1. Totiopotent- the egg and the cells that result from early cell division. Human fertilized egg has the potential to form a whole organism. 2. Pluripotent- forms five days after fertilization (blastocyst- outer layer of cells and inner cell mass). Inner cells form tissue of human. 3. Mulitpotent- pluripotent cells specialize further to give rise to specialized cells. Present in adults. Which type of cells do you think are used for medical therapies? Why? Pluripotent

Cell Cycle Review • Click on the following link, then click on your book and go to Ch. 10 and take the Self-Test and do the Active Art. • Ch. 10 Review

Meiosis and Sexual Reproduction Ch. 9

Meiosis…. Some terms to know • Haploid (1 n)- a cell with only one complete set of chromosomes (gametes or sex cells). Diploid (2 n)- a cell that contains two complete sets of chromosomes. (all other cells) Which are diploid and which are haploid? How do you know sex cells (eggs and sperm) are only haploid?

Homologous Chromosomes come from a Tetrad • Homologous chromosomes are pairs of chromosomes where each one is identical to the other. • A tetrad is a structure containing 4 strands of DNA tightly paired together.

Meiosis • There is a meiosis I and II. Each are the same steps as mitosis. • You begin with one diploid cell and produce 4 haploid. • This gives you many different combinations of genes to be passed on. It’s all chance on the ones you get.

Crossing Over • Occurs during prophase 1 when homologous chromosomes pair up and form tetrads and exchange portions of chromatids.

Meiosis Provides for Genetic Recombination • 1. 28 a Sorting and recombination of genes in sexual reproduction, allows for a great variety of possible gene combinations. • That is why no two people are alike. (Besides identical twins- why? )

1. 46 A great diversity of species increases the chance that at least some living things will survive in the face of large changes in the environment. • Why is this? • So, is diversity good? Give an example.

The Steps…Let’s review. • • Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase. II • What occurs during each step?

Terms to know • Zygote- diploid cell resulting from fusion of egg and sperm: a fertilized egg. • Embryo- early developmental stage of an organism that takes place within an egg, see, or body of its mother. From time of conception to eighth week of pregnancy.

Gamete Formation in Plants • Plant spores- 1 n • Originate in sporophytes (sporeproducing bodies). • Germinate and form gametophytes (gamete producing haploid bodies)

Gamete formation in Animals • Germ cells gametes • Males: spermatocyte enters meiosis and cytoplasmic division making 4 haploid spermatids that develop into sperm.

Females • Germ cell oocyte (immature egg). Makes 3 polar bodies and an ovum (egg) that receives most of the cytoplasm.

1. 8 c Mitosis vs. Meiosis • Mitosis – Somatic cells – One cell division – Two daughter cells with same number of chromosomes as parent. – Daughter cells are identical to parent. • Meiosis – Sex Cells – Two cell divisions – Four daughter cells with half chromosomes as parent – Daughter cells not identical to parents.