Biology Unit 2 Notes and Explanation

Section 5.1 The Cell Cycle “The circle of life!” (skip pg. 1, 2, and 8 in your unit 2 SAW)

The cell cycle is a pattern of growth that all cells follow; just like you have a cycle or routine to do dishes! There are four main stages:

1.) Gap 1 (G1)a.) First stage where cell does its normal duties (contracts, absorbs nutrients, etc)b.) Increases in size and the amount of organelles; most of cycle time spent herec.) Before going on to next stage, have to pass checkpoints (like a driver’s ed course!) like having

enough nutrients or healthy DNA2.) Synthesis (S)

a.) Means “combining of parts to make a whole”

b.) DNA is copied into two complete sets3.) Gap (G2)

a.) Continued normal cell functions along with more cell growth

b.) More checkpoints are met (like behind-the-wheel training before driver’s license test!)

4.) Mitosis (M)a.) Mitosis is the division of the cell nucleus and its

contentsb.) Several mini-stages that dissolves the nuclear envelope (“skin” of nucleus), wraps up DNA and

then separates it into two nucleic.) Cytokinesis is the division of the cell cytoplasm leaving two daughter cells identical to parent

cell

Rate of cell division and size

Cells divide at different rates according to their need and function. For example: skin cells last two weeks, red blood cells last 4 months, and liver cells last up 500 days. G0 stage is where division rarely occurs like neurons.

Cells need to be a certain size which is why they have upper and lower size limits. Think of a car, would it really be functional if it was really small or really big? Cells need to be big enough to have organelles and nutrients to survive.

However, they can’t be too big either! If the ratio of surface area to volume is too small (bloated cell) then materials can’t be diffused/transported quick enough.

**complete p. 3-5 #1-11 with your notes buddy**

Section 5.2 Mitosis and Cytokinesis – Cells copy and then split!

DNA is your blueprint for how your body is built and every cell has a complete set of your DNA. If you took your DNA and stretched it out it would be 3 meters (10 feet) long; or from the ground to the ceiling! All of that can be tightly packed into a microscopic cell.

Chromosomes are long threads of DNA that have certain genes with regulatory information. There are 46 chromosomes in your body cells. Before dividing, the DNA is like spaghetti where it is loosely organized. Once division begins, the DNA wraps around a group of proteins called histones which makes it look like beads on a string.

The DNA keeps wrapping and coiling (like a telephone cord) until you eventually get small, thick rods that look like the letter ‘X’, otherwise known as a chromosome. Each half of the ‘X’ is a duplicate of the other half (DNA copied during S phase), also known as the chromatid. These two chromatids, or “sister” chromatids are held together in the middle by the centromere, a region that looks pinched.

The ends of chromosomes are called telomeres which are made of repeating nucleotides that don’t form genes and prevent chromosomes from sticking together. They also protect important DNA from being lost when it’s copied (like the crust of sandwich bread getting chopped off!).

Draw your Own Chromosome Structure!

Draw a figure of how DNA “coils” into chromosomes; make sure to label the DNA and histones. Then, draw a chromosome structure and label the chromatid, centromere, and telomeres. Use p. 139 as a reference.

The Cell Cycle in Detail – “IPMAT”

You learned about the four main stages of the cell cycle but there are more detailed mini-stages that happen during mitosis. Take a minute and make any words you want for the acronym IPMAT:

I:_________________ P:________________ M:________________ A:________________ T:______________

GAP 1, Synthesis, GAP 2 – getting ready!

Interphase – Gap 1 , Synthesis, and Gap 2 stages fall under interphase, which prepares the cell for division by allowing growth and DNA to replicate (copy).

Mitosis – saying goodbye! Great mitosis video here! http://www.youtube.com/watch?v=LLKX_4DHE3I

Prophase – The DNA coils into chromosomes and the nuclear envelope breaks down. Spindle fibers form (microtubules or “ropes”) that will help move around materials later on.

Metaphase – The spindle fibers “rope” around the centromere (“pinched region”) of the chromosomes and lines them up along the middle of the cell.

Anaphase – The sister chromatids (each half of the ‘X’) separate from each other as the spindle fibers pull them apart towards opposite sides of the cell.

Telophase – Two complete identical sets of chromosomes are at opposite sides of the cell and the nuclear envelope begins to form (nucleus skin). The spindle fibers falls apart and chromosomes uncoil.

Cytokinesis – Splitting up!

Cytokinesis typically happens at the same time as telophase where the cytoplasm is divided and two cells are formed. Then, the cell cycle begins again!

LABEL IT! – Label the stages of mitosis and cytokinesis next to the numbers in the diagram to the right.

WRITE IT! – Turn to page 19 in your unit 2 SAW and complete the chart with your notes buddy!

Section 5.3 Regulation of the Cell Cycle

The Terminator is a movie about a future where robots could no longer be controlled by humans and they rebel! This can happen in your body where cells, if not regulated, can grow out of control and lead to cancer.

Factors that Control Cell Division & Cell Death!

External factors (outside of cell) include physical and chemical signals. A physical example is when cells make contact with each other, they stop dividing (scientists don’t really know why!). Chemical signals are released by growth factors, or a group of proteins that stimulate cell division. An example would be platelets that store growth factors that help your body repair wounds. Internal factors, such as shape changing proteins, can be trigged by external factors that affect the cell cycle.

Apoptosis is when the cell dies. Signals activate genes to make self-destructing enzymes. An example of is when you are an early fetus, you have webbed digits. However, by birth the webbings are gone due to apoptosis!

Benign and Malignant Tumors

Ucontrolled cell division is a class of diseases known as cancer. This occurs when cell regulation is not working properly. As they grow, they form unorganized clumps called tumors. Tumors can be benign, which means harmless and removable since they are typically clumped together. If they are malignant, that means cancer cells have metastasized, or broken away from the tumor and traveled to other parts of the body in the bloodstream.

These cells are harmful because they don’t perform any vital functions and require lots of energy and blood, leaving healthy cells in danger. Cancers cells come from normal cells that have gene damage through mutations. Carcinogens are substances that cause cancers and they range from air pollutants, UV light, and viruses.

**SAW TIME – Complete p.24 in your unit 2 SAW**

Section 5.5 Multicellular Life – Specialization (p 151 text) Skip SAW p. 29-30

Your body is a multicellular organism that is organized in different levels of structure and function.

Example of an organ system in your body:

Cell Differentiation in Stem Cells – From embryo to full grown

All your cells came from a single fertilized egg. From that egg, cells went through a process called cell differentiation where unspecialized (“sleeping”) cells develop (“awake”) and perform their special functions.

Stem cells are special body cells that can:

1.) divide and restore themselves for a long time2.) remain undifferentiated (“asleep”)3.) turn into specialized cells (“awake”)

They are important because they turn into many different specialized cells (“morphing cells”).

** complete p. 31-32 in your SAW with your notes buddy**

Section 6.1 – Chromosomes and Meiosis (skip p.41 in your SAW)

Vocabulary Terms to Know

Somatic Cells – body cells that make up most of your tissues and organs (kidney, skin, blood, etc)

Germ Cells – cells in the reproductive organs that develop into gametes

Gametes – Sex cells located in the eggs and sperm; DNA is passed on to offspring

Homologous chromosomes – “same structure” chromosomes that are in pairs; one from father and one from mother; 23 pairs (46 total) in humans (fruit fly has 4 pairs, 8 total and a fern has 1200 total!).

Autosomes – Chromosomes that do not determine the sex of the organism; numbers 1-22 in humans.

Sex chromosomes – 23rd chromosome that determines sex of organism; known as X and Y chromosomes

FEMALE SEX CHROMOSOMES: _______ MALE SEX CHROMOSOMES: ______

Fertilization – The fusion of an egg and a sperm cell where their nuclei come together to form one nucleus.

Diploid – These are cells that have two copies of each chromosome (one from each parent); represented as 2n. ALL BODY CELLS ARE DILPOID! (germ cells are diploid)

Haploid – These are cells that have only one copy of each chromosome and are represented as n. ALL GAMETES (SEX CELLS) ARE HAPLOID! (remember, germ cells are diploid that make gametes which are haploid)

Meiosis – A form of nuclear division that divides a diploid cell (germ cell) into haploid cells (gametes). This is necessary for sexual reproduction.

Section 6.2 – Process of Meiosis (2 round of division)

Remember that mitosis divides the cells contents and duplicated DNA into two identical cells. In meiosis, you have two rounds of division and the result is 4 unique cells.

Know the difference! Homologous Chromosomes are two separate chromosomes: one from the mother and one from the father. Each half of a chromosome is a sister chromatid.

Meiosis I (round 1)

Prophase I – nuclear envelope breaks down, spindle fibers form, and homologous chromosomes pair up (not done in mitosis).

Metaphase I – The spindle fibers line up the homologous chromosomes randomly in the center of cell (creating genetic diversity).

Anaphase I – Paired homologous chromosomes separate to opposite sides while sister chromatids remain together.

Telophase I – Nuclear membrane forms (skin), spindle fibers break away, and cytokinesis creates two cells with unique combination of chromosomes from parents.

Meiosis II (round 2)

Prophase II – nuclear envelope breaks down, spindle fibers form

Metaphase II – spindle fibers line up the 23 chromosomes at the center

Anaphase II – sister chromatids are pulled apart to opposite sides of cell

Telophase II – nuclear membrane forms, spindle fibers break away, and cytokinesis creates four haploid cells.

KEY DIFFERENCES BETWEEN MITOSIS & MEIOSIS

MITOSIS MEIOSIS

One cell division Homologous chromosomes don’t pair up Sister chromatids separate in anaphase Results in diploid cells

Two cell division Homologous chromosomes pair up Sister chromatids don’t separate in anaphase I Results in haploid cell

**Complete p. 42 and 43 in your SAW with your notes buddy**