Chapter 8 Cell Growth

In most cases, a living thing grows because it produces more and more cells

Limits of Cell Growth

Number 1 Cell membrane- food oxygen and water enter and wastes leave

How fast things enter and leave depends on the surface area How fast products are used up and waste is produced depends on the volume

Fig 8-2 Surface Area and volume do not increase at the same rate so this is a problem

Number 2 All the information a cell needs to survive and function is stored in the DNA When a cell is small enough RNA is made to make all the proteins a cell needs

As a cell gets bigger it does not make more RNA so there is an information crisis As the cell grows there is not enough RNA to support its growth The cell becomes inefficient

The Solution: Cell Division The process where by the cell divides into two daughter cells Draw picture in notes

Rates of Cell Growth E. coli – divides every 30 minutes 1 day – 14kg mass 3 days – mass of earth Ideal conditions do not last long

Controls on Cell Growth Cell behavior – cell growth and cell division are carefully controlled Heart and nervous system – cells rarely divide

Skin and digestive tract – cells divide through life

When cells come in contact with other cells they stop growing Scientists are still working on why this is true

Cell growth can be turned on Example – a cut, broken bone Cell growth stops when fixed

Uncontrolled Cell Growth Results are severe Cancer – disorder where cells have lost the ability to control their own growth

8-2 Cell Division: Mitosis and Cytokinesis

Eukaryotic Cells Nucleus and membrane bound organelles Eukaryotic cells divide in two steps

1. Mitosis – the process by which the nucleus of a cell is divided into 2 nuclei, each with the same number and kinds of chromosomes as the parent cell

2. Cytokinesis – process of the cytoplasm dividing to form 2 new cells

The process is complex Large amounts of DNA need to be separated. Each cell needs one copy of a chromosome

Chromosomes Structures in the cell that contain the genetic information that is passed from one generation to the next

The cells of different organisms contain different numbers of chromosomes Humans – 46 Goldfish – 94 Dog – 78 Cat – 32

Chromosomes are made of chromatin. Chromatin is made of DNA and proteins.

When a cell is not dividing chromatin is lose and spread out When a cell is going to divide chromatin condenses and chromosomes become visible

The proteins in chromatin help in the folding of DNA. Helps it fit and keeps it organized. Total length of DNA 10,000x the length of a chromosome

Histones Circular proteins that the DNA is wrapped around

Nucleosome Bead like structures of DNA wrapped around a few histones

Chromosome Structure Ready to divide DNA replicated Chromosomes become visible by condensing

Section 8.2 Summary – pages 201 - 210 The structure of eukaryotic chromosomes Centromere Sister chromatids Supercoil within chromosome Chromosome Continued coiling within supercoil Histone H1 Nucleosome DNA Section 8.2 Summary – pages 201 - 210

The chromosome has two identical parts – 2 Chromatids

The two chromatids are often called sister chromatids Centromere – holds sister chromatids together

The Cell Cycle

The period of time from one mitosis to the next A cell grows, prepares for division, and divides to form two daughter cells Includes mitosis

                               ` Mitosis – M phase

Interphase G1 – growth and activity S- DNA replication G2 – growth and activity

Some cells in the body go through the cell cycle every 6 hours Some cells never do (nerve and muscle)

Interphase Long Period between cell divisions 3 phases – G1, S, G2 G1 – (gap1) – growth and development

S (DNA synthesis phase) – replication Proteins associated with chromosomes are also made G2- gap 2 – shortest phase Synthesis of materials needed for cell division

During interphase the cell is active Proteins are made DNA is copied ATP is made and used Cells that are specialized do their thing Example - secretion

Do Now What are the 2 phases of the cell cycle? What happens in g1? What happens in S phase? What happens in the g2 phase? What is chromatin? What are histones and nucleosomes? What do uncopied chromosome s look like? What do copied chromosomes look like? How many chromosomes do humans have?

Mitosis is divided into 4 stages.

Prophase (Ready) Metaphase (Middle) Anaphase (away) Telophase (two)

Prophase Longest phase 50-60% of total mitosis time Chromosomes become visible – coil tightly Centrioles separate and move to opposite sides

Chromosomes attach to the spindle Nucleolus disappears Nuclear envelope breaks down

Spindle Meshlike structure that develops from the centrioles Helps chromosomes move

Metaphase Shortest – few minutes Chromosomes line up at the center of the cell

Anaphase Centromeres that join sister chromatids split Sister chromatids separates into individual chromosomes Chromosomes separate into two groups near the poles

Over when chromosomes separate

Telophase Chromosomes loosen up – go back to chromatin Occurs in the area where the nucleus will form Nuclear envelope reforms Nucleolus becomes visible Mitosis is over

Cytokinesis Last step in cell division Two nuclei form – each with a set of chromosomes Cytokinesis – division of the cytoplasm

Animal Cells – cell membrane pinches in Plant cells – cell plate forms down the middle The cell wall forms in the cell plate

Plant Cell undergoing Mitosis

Mitosis Movie

9-3 Meiosis A type of cell division that gametes (eggs and sperm) undergo

A cell has two copies of each chromosome. Humans have 46 chromosomes or 23 pairs.

Homologous Chromosomes Two chromosomes that make up a pair Carry the same types of information One originally came from mom and one originally came from dad

Diploid A cell with pairs of chromosomes One from mom and one from dad Diploid number for humans is 46

Haploid A single set of chromosomes 1N

Autosomes Body cell chromosomes Humans have 22 pairs

Sex Chromosomes X and Y Humans have two Females have 2 X chromosomes Males have an X and Y chromosome

Karyotype A picture of all of the chromosomes found in one cell. Can be used to determine gender and genetic diseases.

Meiosis 2N produces 1N Process of reduction division in which the number of chromosomes per cell is cut in half 2 rounds of cell division Meiosis I and Meiosis II Produces gametes (eggs and sperm)

Meiosis I Prophase I Metaphse I Anaphase I Telophase I Tetrad

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Meiosis II Prophase II Metaphase II Anaphase II Telophase II Telophase II produces gametes (IN) (eggs or sperm)