Provide 2 reasons you think cells might divide? Unit 4: Genetics Provide 2 reasons you think cells might divide?

Notes: Intro to Chromosomes & the Cell Cycle EQ: How and why do cells divide?

The Cell Cycle: Process in which cells grow, prepare for division, and divides to form two daughter cells. Reasons cells divide: 1. Size (Surface area to volume ratio) 2. Reproduction ( Asexual vs Sexual) 3. Growth & Development (Multicellular) 4. Repair and Replacement of tissue

**Reminder** DNA is contained in the nucleus… but, DNA can look different depending on what you are interested in…

We are going to focus on… CHROMOSOMES! This is a chromosome! It contains your genetic information centromere Each side is a sister chromatid. They contain identical information.

Sister chromatids are held together by a centromere Chromosomes: Sister chromatids are held together by a centromere A duplicated chromosome is made of 2 sister chromatids Sister chromatids are IDENTICAL A single sister chromatid can also be referred to as an unduplicated chromosome

How many chromosomes does a human have? 46! 23 from your mom 23 from your dad You have 23 pairs of homologous chromosomes

These chromosomes are HOMOLOGOUS Same size Same shape Same type of information Example: A = dimples Dad has dimples a = no dimples Mom does not have dimples

Cells constantly need to make new cells Cells constantly need to make new cells. Each new cell must have identical DNA to the old cell. How is this accomplished in living organisms? THE CELL CYCLE!

Cell Cycle & Mitosis Interphase: a period of growth and preparation for division in cell Mitosis: the division of the cell nucleus (eukaryotic cells)

1. Fold your paper into 8 boxes

2. Cut your paper down the middle horizontal line

3. Tape the two strips of paper together where the dashed line is

4. Draw the lines and label each section --------- INTERPHASE -------- ----------- MITOSIS (PMAT) ------------- CYTO- KINESIS

G1 = growth 1 (Interphase) Cell grows in size Organelles and proteins made

S = synthesis(Interphase) DNA is replicated (“synthesized”) Each chromosome duplicates to make a sister chromatid 2x as much DNA at the end of synthesis

G2: growth 2 (Interphase) Continued cell growth Organelles and molecules needed for division are produced

Prophase (Mitosis) Nucleus disappears Chromosomes condense and become visible Centrioles move to opposite sides of cell Spindle starts to form X X X

Metaphase (Mitosis) X X X Chromosomes line up in the middle Spindle fibers connect centriole to centromere X X X

< < < < < < Anaphase (Mitosis) Sister chromatids separate (break apart) as spindle fibers pull them to opposite sides of cell Chromatids look like “A” < < < < < <

Telophase (Mitosis) Chromosomes are at opposite sides of the cell Nuclear membrane reforms Chromosomes unwind Spindle breaks apart Nucleolus visible in each daughter cell < < < < < <

Cytokinesis: Division of the cytoplasm and organelles Animal: Division of the cytoplasm and organelles and pinching off into 2 IDENTICAL daughter cells. Plant: Cell plate forms and creates a new cell membrane to make 2 IDENTICAL daughter cells

Cell Cycle Overview

Cell Cycle Follow-Up Questions Homework!