Friday in Biology Get out journal Pick up scissors and glue

First page of Journal ____your name’s __________ Biology Journal Biology Wikipage

THE CELL CYCLE and Mitosis: Cells at Work!!

Review: DNA & Chromosomes DNA – the molecule that carries the genetic information Ex. The toilet paper Gene – a section of DNA that codes for a protein/trait Ex. A small piece of toilet paper Histone – Proteins that the DNA wraps around to form chromosomes Ex. The toilet paper roll Chromosome – a long DNA molecule found in the nucleus Ex. The toilet paper on the toilet paper roll

Chromosome Structure Sister chromatids – duplicated chromosomes that are attached to each other Centromere – narrow waist where sister chromatids are attached

Chromosome Structure Telomeres – ends of chromosomes that protect DNA from damage (hard hats) Kinetochores – disc-shaped proteins that attach chromosomes to the spindle (handles)

Chromosomes vs. Chromatin Chromosomes -Toilet paper on the toilet paper rolls -Organized for distribution (information cannot be used) -Mitosis Chromatin -large pile of toilet paper unwound off the roll -information in DNA can be used by cell -Interphase

What is the cell cycle? Continuous sequence of growth and division of a cell. 2 parts: Interphase & Mitosis Busiest and longest section is INTERPHASE After DNA is replicated (during Interphase), mitosis can begin

Cell Cycle

Interphase: first phase of Cell Cycle G 1 phase – cell grows, makes proteins and other products, and does its cell business S phase – “synthesis” phase, when chromosomes (DNA and histone proteins) are replicated G 2 phase – cell prepares for division Centrosomes and centrioles replicate Proteins associated with division accumulate

Cell Cycle – Mitotic Phase Mitosis – division of the nucleus and the chromosom es within it Cytokinesis – division of the cytoplasm

What is Mitosis?? Part of the cell cycle Nuclear cell division during which chromosomes are equally distributed to the 2 identical daughter cells that are formed Results in growth Continuous process 4 stages

Stage 1: Prophase Chromatin coils up into chromosomes Nucleus begins to disappear Centrioles migrate to opposite ends of cells and spindle forms

Stage 2: Metaphase Chromosomes attach to spindle fibers Chromosomes line up along the equator of the spindle Very short phase

Stage 3: Anaphase sister chromatids separate Centromeres split apart Chromatids are pulled to opposite poles of the cell

Stage 4: Telophase chromatids reach the poles Chromosomes unwind and spindle breaks down New nuclei form around each set of chromosomes Plasma membrane separates

Cytokinesis: Division of the cytoplasm Animal cell Plasma membrane pinches along equator Forms a cleavage furrow that deepens until the cell is pinched in two Plant cell Plasma membrane does not pinch in b/c of rigid cell wall Cell plate forms at the equator that divides the cytoplasm

I Pour Milk And Tea I—Interphase “The Xerox phase” P—Prophase “Cell PREPARES and chromosomes become visible” M—Metaphase “The chromosomes line up in the MIDDLE” A—Anaphase “The chromosomes pull APART” T—Telophase “The TWO identical daughter cells separate”

Purpose of Mitosis (Cell Division) DNA makes an exact copy of itself so that AFTER mitosis, the 2 new daughter cells will be identical. The process of mitosis ensures that each new cell receives the correct number of chromosomes for that organism (Humans = 46 chromosomes) 23 from mom, 23 from dad When both sets of chromosomes are in a cell, it is said to be diploid. All somatic (body) cells are diploid.

Cell Cycle Regulation

Internal check points External cues Cyclin and kinases (proteins) that are made during G 2 phase

Cancer Cancer cells do not respond to cell cycle signals – they divide continuously divide or they stop and start dividing at random places in the cell cycle