1.6 Cells Study Guide

Compare Somatic Cells and Gametes

Somatic cells are body cells and gametes are our sex cells, or sperm and eggs. Somatic cells have a diploid genome. This means that they get two copies of each chromosome, one from mom and one from dad. Gametes on the other hand are formed through a process called meiosis, which creates a haploid genome.

Compare Chromatin and Sister Chromatids

Chromatin is a substance made up of DNA or RNA and proteins, while Sister Chromatids are two identical halves of a chromosome that has been replicated in preparation for cell division. The two “sister” chromatids are joined at a constricted region of the chromosome called the centromere.

What is interphase and how is it divided?

Interphase is when the cell is doing it’s everyday job, such as producing RNA and synthesizing proteins and enzymes. It is divided into 3 phases, G1, S, and G2.

Describe the G1 phase

They get bigger in size and make proteins and organelles needed for normal functions of DNA synthesis. (everything except chromosomes are duplicated)

Describe the S phase

The cell replicates the DNA (There is an error rate of ~1 per 100 million)

Describe the G2 phase

A period of rapid cell growth and protein synthesis during which the cell prepares itself for mitosis

Describe the G0 phase

The phase in the cell cycle in which the cell is neither dividing nor preparing for divisio

PROPHASE/”PROMETAPHASE”

• Centrioles move to opposite sides of the cell

• The nuclear membrane breaks down

• Nucleolus disappears

• Mitotic spindle forms/attach between two centrosomes

  • this creates kinetochores (proteins that help pull them apart)

• Microtubules attach at the kinetochores

• Chromosomes begin moving to each side

• Chromosomes become shorter and fatter by coiling

METAPHASE

• Chromosomes align along the middle of the cell

• Spindle fibers coordinate movement

  • this ensures chromosomes separate properly

ANAPHASE

• Sister chromatids separate at kinetochores

• move to opposite poles and are pulled at the centromeres by motor proteins (actin, myosin)

• The poles move further apart

• Proteins that hold chromatids together are inactivated

TELOPHASE

• Chromosomes arrive at opposite poles

• Nucleoli form

• Chromosomes disperse

• Spindle fibers disperse

Why do cells divide?

Reproduction, Growth, Repair and Renewal

Nucleus

F: Protects DNA

S: Nuclear Envelope, membrane fused in spots to create pores which allows large molecules in

Cytoskeleton

F: Maintains the shape of the cell through microfilaments (smallest), intermediate filaments, and microtubules (largest). Helps in locomotion and organization of structures in the cell

Centrioles

F; Helps in cell division, organizes microtubules, guides chromosomes in mitosis

S: made of microtubules

DNA organization

• DNA is organized in Chromosomes

  • wrapped around HISTONE proteins

  • DNA-protein complex: CHROMATIN

Explain how chromosomes move to their poles

As mitosis progresses, the microtubules attach to the chromosomes, which have already duplicated their DNA and aligned across the center of the cell. The spindle tubules then shorten and move toward the poles of the cell. As they move, they pull the one copy of each chromosome with them to opposite poles of the cell.

Cytokenesis in animals

Belt of actin microfilaments create a cleavage furrow which splits the cell into two

Cytokenesis in plants

A cell plate forms when the vesicles line up and create a new cell wall

Explain the differences in division between nerve cells and liver cells

nerve cells do not divide at all (in G0), while liver cells will divide onc every year or two

G1 cell cycle checkpoint

Checks the cell size, make sure the nutrients are sufficient, check the DNA (is it damaged), and make sure the cell is receiving the correct cues. This checkpoint determines if the cell goes back into G0 or it goes forth with division. (Gene p53 halts cell division for damaged DNA)

G2 cell cycle checkpoint

Checks if the DNA is in tact and if the DNA is properly replicated

Spindle cell cycle checkpoint

The cell examines whether all the sister chromatids are correctly attached to the spindle microtubules

Cyclins and Cyclin dependant kinases

Cyclins drive the events of the cell cycle by partnering with a family of enzymes called cyclin-dependent kinases (Cdks). A lone Cdk is inactive, but the binding of a cyclin activates it, making it a functional enzyme and allowing it to modify target proteins.

Growth factors

• Coordination between cells

• protein signals released by body cells that stimulate other cells to divide

  • density-dependent inhibition

    • cells stop dividing

  • anchorage dependence

    • cells must be attached to a substrate

Explain cancer and how cancer cells form

Cancer is a disease caused when cells divide uncontrollably and spread into surrounding tissues. There are six key mutations

• unlimited growth (turned on growth promoter genes)

• Ignore checkpoints (turned off tumor suppressor gene)

• escape apoptosis (turn off suicide gene)

• immortality = “unlimited divisions” (turn on chromosome maintence genes)

• promotes blood vessel growth (turn on blood vessel growth genes)

• overcome anchor & density dependence (turn off touch sensor genes)

What causes the mutations?

1. UV Radiation

2. chemical/radiation exposure

3. heat

4. cigarette smoke

5. pollution

6. age

7. genetics

how are cancer cells different from normal cells

Unlike healthy cells, cancer cells don't carry on maturing or become so specialised. Cells mature so that they are able to carry out their function in the body. This process of maturing is called differentiation. In cancer, the cells often reproduce very quickly and don't have a chance to mature.

Oncogenes

Cancer can arise when a proto-oncogene is mutated, changing it into an oncogene and causing the cell to divide and multiply uncontrollably.

Tumor supressors

When a tumor suppressor gene is inactivated by a mutation, the protein it encodes is not produced or does not function properly, and as a result, uncontrolled cell division may occur.

“Go-Ahead” signals

Protein signals (Activators/Inhibitors) that promote cell growth/division. “Promoting Factors” (Internal) and “Growth Factors” (External).

“Primary mechanism of control” - Phosphorylation (Kinase enzymes)

Scientists

Checkpoints - Leland L. Hartwell

Cdks - Tim Hunt

Cyclins - Sir Paul Nurse

Tumors

• Mass of Abnormal Cells

  • Benign Tumor

    • An abnormal clump of cells that does not spread

  • Malignant Tumor

    • Cells leave the original site and spread through blood/lymph nodes

    • impair functions in the body