Cell Growth and Division Ch 10 Cell Size

Cell Growth and Division Ch. 10

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) Not much variation. b. Sexual- produces offspring that have a combination of genetic material from two parent organisms. Lots of variation.

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. • When chromatin coils it becomes _______?

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.

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.

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. • The spindle forms and attaches to the centrioles and centromere.

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. • 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.

Cell Cycle Regulators • Cyclins are proteins that regulate the timing of the cell cycle in eukaryotic cells. • Internal Regulators- proteins that respond to events inside the cell. Allow cell cycle to proceed only when certain processes have happened. • 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. • 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.

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 fertlization (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