CELL CYCLE NOTES – UNIT 6



CELL CYCLE NOTES – UNIT 6

1. WHY ARE CELLS SO SMALL?

A. They obtain nutrients/oxygen by diffusion

B. They get rid of wastes by diffusion

C. Water balance is controlled by osmosis

D. If they get too large, diffusion/osmosis can’t happen fast enough to keep them alive

E. Therefore, they will “split in half” before they get too large (more on this later)

2. WHAT IS THE “CELL CYCLE?”

A. Basically it is the life cycle of a cell

B. Includes: Interphase (G1, S, G2), Mitosis, and Cytokinesis (these are the parts of the cell cycle)

C. Summary: a parent cell grows, make a copy of all DNA, split in half to make two identical daughter cells

3. WHAT ARE CHROMOSOMES?

A. Humans have 46 chromosomes; they are arranged in 23 pairs (like shoes)

B. Pairs 1-22 are known as autosomes; used in making cells, keeping us alive, etc.

C. 23rd pair is known as the sex chromosomes; used to reproduce (make new humans!)

D. Female sex chromosomes are “XX;” male sex chromosomes are “XY”

E. Chromosomes carry genetic information (DNA); this is the genetic code for life!

4. WHAT IS A CHROMOSOME MADE UP OF?

A. A chromosome has two halves (left and right side) called sister chromatids

B. Sister chromatids are connected by a centromere

C. Chromatids are made up of unbelievable amounts of material called DNA

D. DNA is tightly coiled around proteins called histones

E. DNA consists of segments called genes

F. DNA, again, is the genetic code used to build proteins/living material

5. WHAT IS GOING ON IN THIS THING CALLED THE CELL CYCLE?

A. G1 – the cell is basically growing, and preparing the chromosomes for replication

B. S – the cell is making a copy of all DNA (replicating)

C. G2 – the cell continues to grow and make final preparations for Mitosis

D. G1, S, G2 are all known as INTERPHASE

E. Mitosis occurs (includes the steps prophase, metaphase, anaphase, and telophase)

F. Cytokinesis is when the cell actually divides into two cells

G. Mitosis and Cytokinesis together make up what is known as the “M” phase

i. Mitosis is the division of the nucleus

ii. Cytokinesis is the division of the cytoplasm

6. WHAT IS THE RESULT OF THE CELL CYCLE?

A. Cells split before they get too large to survive

B. Each original parent cell splits to become two identical daughter cells

C. The cell cycle (mitosis) makes new body cells, which are everything except reproductive cells (sperm/egg)

D. Cell cycle allows four things to happen:

1. Growth (more cells means organisms increase in amount of living material)

2. Repair (replace dead/damaged cells)

3. Reproduction (reproduces at the cellular level; asexual reproduction in single-celled organisms)

4. Keeps our cells small; this allows them to diffuse needed materials fast enough to stay alive!

7. TIME TO DRAW WHAT’S ON THE BOARD NOW!

8. MEIOSIS – HOW GAMETES (SEX CELLS) ARE MADE

A. Gametes is a fancy name for sex cells; sperm (male sex cells) and eggs (female sex cells)

B. Each original parent cell will replicate once, then split twice to form four (4) daughter cells

C. The four daughter cells produced will contain ½ as many chromosomes as the parent cell (because of the two cell divisions that occur)

D. Gametes are haploid (n), meaning that they contain one copy of each chromosome

E. Somatic cells are diploid (2n), meaning that they contain two copies of each chromosome

F. The haploid (n) number for humans is 23; the diploid (2n) number for humans is 46

G. Why do gametes contain the haploid number of chromosomes (1/2 as many as somatic cells)?

***so that when a sperm cell (with its ½ set of chromosomes-“n”) joins with an egg cell (with its ½ set of chromosomes-“n”), the resulting zygote will have a full set of paired chromosomes (diploid-“2n). For example, when a haploid human sperm cell with 23 chromosomes joins with a haploid human egg cell with 23 chromosomes, the zygote (baby) will have 46 chromosomes, which is the correct diploid number for humans.

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