MRS. WILLIAMS FRESHMAN BIOLOGY - HONORS SEMESTER TWO Chapter 5: Cell Growth and Division

Origin Statement – November 18 th, 2013 If you’re a cell, is it better to be small or large?  Justify your answer! How do organisms grow? Do the cells that they have get bigger or do they grow more cells? In your own words, describe “cell division”.

Introduction Intro to the Cell Cycle with Bill Nye

Cell Growth Most living things grow by producing more cells. Cells don’t necessarily get larger, there are just more of them. As cells get bigger, their volume increases much faster than their surface area. Reasons why cells DIVIDE rather than grow larger:  The bigger the cell, the more demands the cell places on the DNA  The bigger the cell, the more trouble the cell has moving enough nutrients and wastes across the cell membrane  The bigger the cell, the more quickly food and oxygen are used up

RA Activity Turn to page 136 in the Alligator text  Read “Cell Size is Limited” (second half of page 136 through page 137) with your partner and do a Think Aloud.  Focus on the ratio of surface area to volume in cells and discuss how that relates to cell growth  Think, Pair, Share

Chromosomes In eukaryotic cells, genetic info that is passed from one generation to the next is carried on chromosomes Made up of DNA and proteins Each cell has a specific number of chromosomes (humans have 46) Before cell division, each chromosome is copied in to two sister chromatids that hold identical genetic info One chromatid goes to each of the new cells

Diploid vs. Haploid Diploid (2n) cells have two sets of chromosomes  One inherited from mom; one from dad All somatic (body) cells are diploid (all cells except sex cells) Humans’ diploid number is 46, but other species have other numbers. The chromosomes that are alike from each set are called homologous chromosomes. Haploid (1n) cells have one set of chromosomes Gametes (sex cells) are haploid Humans’ haploid number is 23, but other species have different numbers. When fertilization occurs, the organism will again be diploid.  23 chromosomes from male parent + 23 chromosomes from female parent = 46 total (diploid)

Chromosome Structure

Chromosome Structure Continued Before replication  Each chromosomes is a single strand After replication  Each chromosome is made of two identical copies stuck together by a centromere  Each copy is called a sister chromatid

The Cell Cycle A series of events that cells go through as they grow and divide During the cell cycle, a cell:  Grows  Preps for division  Divides to form two daughter cells (has nothing to do with gender!)

Phases of the Cell Cycle There are three main phases of the cell cycle  1. Interphase  G1 SS  G2  2. Mitosis  Prophase  Metaphase  Anaphase  Telophase  3. Cytokinesis

Interphase Interphase: divided into three phases – G 1, S, G 2 G 1  Gap phase  Cell grows and carries out normal function  Some cells may stay in G1 indefinitely (called G 0 ) S  Synthesis phase  Chromosomes replicate  DNA synthesis takes place G 2  Gap phase  Cell grows and carries out normal functions  Other organelles replicate

Cell Division Happens in two stages:  Mitosis  Cytokinesis Mitotic reproduction is asexual since the new cells produced are genetically identical to the parent cell

Origin Statement – 11/20/13 What are the three major stages of the cell cycle? Draw a picture showing the following:  A chromosome before replication  A chromosome after replication  Sister chromatids  Centromere What is the difference between haploid and diploid cells? What happens during S phase of interphase?

Exit Slip Without the use of your notes, answer the following on a scrap piece of paper that you CAN turn in: 1. What is the difference between a haploid and a diploid cell? 2. Name the three stages of interphase and describe what happens during each.

Review (from exit slips) Haploid  One SET of chromosomes – not one chromosome! Diploid  Two SETS of chromosomes – not two chromosomes! Not all organisms have 46 chromosomes per cell! Stages of Interphase  G 1 – Cell grows and carries out normal function  S – DNA is replicated/synthesized  G 2 – Cell grows, carries out normal function, and organelles are replicated

Cell Division Mitosis  Division of the nucleus  Occurs in somatic cells (body cells, NOT sex cells)  One division with 4 phases, creating 2 identical daughter cells  Cells start diploid and end diploid! Cytokinesis  Division of the cytoplasm

Mitosis Four Phases  Prophase  Metaphase  Anaphase  Telophase Refer to page 141 in your “Alligator” text for great pictures!

Mitotic Phases in Detail: Phase One Prophase  Chromatin condenses into chromosomes  Centrioles separate  Spindle begins to form  Nuclear envelope breaks down

Mitotic Phases Detailed: Phase Two Metaphase  Chromosomes line up across the center of the cell  Each chromosome is connected to a spindle fiber at its centromere

Mitotic Phases Detailed: Phase Three Anaphase  Spindle fibers shorten and pull apart the sister chromatids  Individual chromosomes are moved apart

Mitotic Phases Detailed: Phase Four Telophase  Chromosomes gather at opposite ends of the cell and lose their distinct shapes  Two new nuclear envelopes form  Mitosis Online Lab Mitosis Online Lab  Mitosis with Tim & Moby Mitosis with Tim & Moby

Cytokinesis NOT part of mitosis; last step of cell cycle During cytokinesis:  The cytoplasm pinches in half  End product: 2 daughter cells that are IDENTICAL to the parent cell (so if parent has 46 chromosomes, each daughter cell has 46 chromosomes!)  Varies slightly in animal and plant cells

Cytokinesis in Plant and Animal Cells Animals  In most animal cells, the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts  Each part contains its own nucleus and organelles Plants:  A cell plate forms midway between the divided nuclei  Cell plate gradually develops into a separating membrane  Cell wall begins to appear in the cell plate

Cell Division Controls and Problems Generally, when cells come into contact with other cells, they stop growing Timing of cell growth regulated by proteins called cyclins See fig. 5.10, page 146 Sometimes cells don’t respond to the signals that regulate the growth of most cells This can lead to cancer – a disorder in which some of the body’s own cells grow out of control p53 is a gene that halts the cell cycle until all chromosomes are replicated; found to have mutations in cancer patients These cells grow uncontrollably and form masses called tumors

Cell Cycle Flow Map Create a Flow Map showing the 6 major steps of the cell cycle Each large box should have a picture of what the cell looks like in that stage The small boxes beneath should describe what happens during that step!

CHAPTER 6, SECTIONS 1 & 2 Meiosis

Comparing Mitosis and Meiosis During the video, take notes comparing the two processes These notes will be useful for a later activity, so be thorough! Mitosis/Meiosis Video

Characteristics of Meiosis Meiosis occurs in gametes (sex cells) ONLY TWO divisions with 4 phases each (8 phases total) creating 4 unique cells Cells start out diploid and end haploid

Meiosis I: Prepping for Meiosis Interphase I  Cells replicate DNA ONCE, forming duplicate chromosomes There will only be ONE interphase during the whole process of meiosis. Meiosis I has four stages:  Prophase I  Metaphase I  Anaphase I  Telophase I Cytokinesis Page , figure 6.5 (A)

Meiosis I: Stage One Prophase I  Each chromosome (2 sister chromatids) pairs with its corresponding homologous chromosome to form a tetrad  Crossing-over occurs  Results in the exchange of alleles between homologous chromosomes and produces new combos of alleles

Meiosis I: Stage Two Metaphase I  Spindle fibers attach to the chromosomes  Still attached at the centromere

Meiosis I: Stage Three Anaphase I  Spindle fibers pull apart homologous chromosomes toward opposite ends of the cell

Meiosis I: Stage Four and Cytokinesis Telophase I  Nuclear membranes form Cytokinesis  The cytoplasm separates (just like in mitosis)  Cell splits into two haploid (n) cells

Meiosis II Meiosis II is very similar to mitosis; however there is NO chromosome replication that takes place before it begins (no interphase II) Both haploid (n) cells created in meiosis I divide Ends with four new haploid (n) cells  Sperm or egg cells Four stages:  Prophase II  Metaphase II  Anaphase II  Telophase II Cytokinesis

Meiosis II: Stage One Prophase II  The two haploid (n) daughter cells that were produced at the end of meiosis I have half the number of chromosomes as the original cell  NO REPLICATION OF CHROMOSOMES happens during meiosis II

Meiosis II: Stage Two Metaphase II  Chromosomes line up in the center of each cell  Spindle fibers are attached at centromeres of sister chromatids  Like metaphase in mitosis

Meiosis II: Stage Three Anaphase II  Spindle fibers shorten  Sister chromatids separate and move toward opposite ends of each cell

Meiosis II: Stage Four and Cytokinesis Telophase II  Nuclear envelopes reform in both cells Cytokinesis  The cytoplasm in both cells splits to form 4 haploid (n) daughter cells with HALF the number of chromosomes as the original cell  So if parent cell has 46 chromosomes, each cell at the end of meiosis II would have 23 chromosomes.

Origin Statement – November 26 th What are the steps of the cell cycle, in order? What two steps make up what is referred to as “cell division”? What type of reproduction is mitosis? Meiosis? List three similarities and three differences between mitosis and meiosis.

Spermatogenesis & Oogenesis Spermatogenesis  Formation of sperm  Starts at puberty  Forms 4 sperm during each meiosis  Men will make 5 to 200 million sperm per day!! Oogenesis  Formation of the egg  Meiosis starts inside the womb and continues in some during every cycle after puberty  1 egg and 3 polar bodies are created after every meiosis  The egg must contain a lot of cytoplasm to support the developing embryo after fertilization  Fig. 6.6, page 176