The Cell Cycle & Cancer: Study Guide and Learning Targets

Unit 2: The Cell Cycle & Cancer

Overview

This unit covers the structure and function of chromosomes, the stages of the cell cycle, DNA structure and replication, and the regulation of the cell cycle, including how disruptions can lead to cancer. Understanding these concepts is fundamental to cell biology and genetics.

Learning Target Topic A: The Cell Cycle

Chromosome Structure

• Chromosome: A thread-like structure composed of DNA and proteins (histones) that carries genetic information.

• Sister Chromatids: Identical copies of a chromosome connected by a centromere after DNA replication.

• Centromere: The region where sister chromatids are joined together.

• Replicated Chromosome: A chromosome that has been copied and consists of two sister chromatids.

Stages of the Cell Cycle

• Interphase: The phase where the cell grows, performs normal functions, and replicates its DNA. It consists of three sub-phases:

  • G1 (Gap 1): Cell growth and normal metabolic roles.

  • S (Synthesis): DNA replication occurs.

  • G2 (Gap 2): Preparation for mitosis; further growth and protein synthesis.

• Mitosis: The process of nuclear division, divided into four main stages:

  • Prophase: Chromosomes condense, nuclear envelope dissolves, spindle forms.

  • Metaphase: Chromosomes align at the cell's equator.

  • Anaphase: Sister chromatids separate and move to opposite poles.

  • Telophase: Nuclear envelopes reform around separated chromosomes.

• Cytokinesis: Division of the cytoplasm, resulting in two daughter cells.

Comparison of Interphase and Mitosis

• Interphase: Cell grows and replicates DNA; chromosomes are not visible.

• Mitosis: Cell divides its nucleus; chromosomes are visible and separated.

Example:

During the S phase of interphase, a human cell replicates its 46 chromosomes, resulting in 92 chromatids. During mitosis, these chromatids are separated into two identical sets.

Learning Target Topic B: DNA & Replication

DNA Structure

• DNA (Deoxyribonucleic Acid): A double helix composed of nucleotides, each containing a phosphate group, deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, guanine).

• Base Pairing: Adenine pairs with thymine (A-T), and cytosine pairs with guanine (C-G) via hydrogen bonds.

• Antiparallel Strands: The two DNA strands run in opposite directions (5' to 3' and 3' to 5').

DNA Replication

• Semi-Conservative Replication: Each new DNA molecule consists of one original strand and one new strand.

• Key Enzymes:

  • Helicase: Unwinds the DNA double helix.

  • DNA Polymerase: Synthesizes new DNA strands by adding nucleotides.

  • Primase: Synthesizes RNA primers to initiate DNA synthesis.

  • Ligase: Joins Okazaki fragments on the lagging strand.

• Replication Fork: The Y-shaped region where DNA is split into two strands for copying.

• Okazaki Fragments: Short DNA fragments synthesized on the lagging strand.

DNA Replication Equation

$\text{DNA}_{\text{parent}} \xrightarrow{\text{Replication}} \text{DNA}_{\text{daughter}}$

Example:

During replication, DNA polymerase adds nucleotides to the 3' end of the new strand, using the original strand as a template.

Learning Target Topic C: Cell Cycle Regulation and Cancer

Cell Cycle Regulation

• Checkpoints: Control points (G1, G2, M) where the cell assesses whether to proceed with division.

• Regulatory Proteins: Cyclins and cyclin-dependent kinases (Cdks) regulate progression through the cell cycle.

• Tumor Suppressors: Proteins (e.g., p53, BRCA1) that prevent uncontrolled cell division.

• Contact Inhibition: Normal cells stop dividing when they touch other cells.

• Apoptosis: Programmed cell death to eliminate damaged or unnecessary cells.

Cancer and the Cell Cycle

• Cancer: A disease caused by uncontrolled cell division due to mutations in genes regulating the cell cycle.

• Oncogenes: Mutated proto-oncogenes that promote excessive cell division.

• Loss of Tumor Suppressors: Leads to failure in cell cycle control and increased risk of cancer.

• Telomerase: Enzyme that extends telomeres, allowing cancer cells to divide indefinitely.

Example:

Mutations in the p53 gene can prevent apoptosis, allowing damaged cells to proliferate and form tumors.

Key Vocabulary and Root Words

Term	Definition
Okazaki fragment	Short DNA segment synthesized on the lagging strand during replication
DNA polymerase	Enzyme that synthesizes new DNA strands
RNA primer	Short RNA sequence that initiates DNA synthesis
Helicase	Enzyme that unwinds the DNA double helix
Ligase	Enzyme that joins DNA fragments together
Proto-oncogene	Normal gene that can become an oncogene when mutated
Tumor suppressor	Gene that inhibits cell division and prevents tumor formation
Apoptosis	Programmed cell death

Root Words

• Helic-: spiral

• Lig-: bound or tied

• Mut-: change

• Semi-: half

• Carcino-: cancer

• Onco-: tumor

• Proto-: first, original

Study and Exam Preparation Tips

• Review all activities, notes, labs, and answer keys.

• Read your notes and assigned textbook chapters.

• Practice with worksheets and lab activities.

• Focus on the main topics: Cell Cycle, DNA & Replication, Cell Cycle Regulation/Cancer.

• Use animations and online resources for visual understanding.

Exam Format

• 40 minutes total

• 20 multiple choice questions (+20 points)

• 1 short answer prompt (+20 points)