cells III

Cancer Overview

• Definition of Cancer: Uncontrolled division and spread of cells in the body.

• Neoplasm: Another term for tumor; represents a mass of rapidly replicating cells.

Types of Neoplasms

• Benign Tumors:

  • Defined as non-cancerous masses.

  • Have an encapsulating protein wall preventing spread.

  • Rapidly growing but retain some normal cell function, e.g., liver function.

  • More uniform cell structure similar to surrounding healthy cells.

• Malignant Tumors:

  • Defined as cancerous masses.

  • Lack encapsulating walls, allowing for metastasis (spread to other parts of the body).

  • Irregular cell shape and structure; cells do not function normally.

Characteristics of Cancer Cells

• Nutrient Competition:

  • Cancer cells take up resources such as sugars and oxygen, depriving normal cells.

  • They consume more blood flow and nutrients through diffusion than normal cells.

• Physical Presence:

  • Tumors occupy space, causing pressure on nearby healthy cells (e.g., neurons).

  • Pressure can lead to cell death and systemic damage, particularly in sensitive areas like the brain.

• Lack of Normal Cell Control:

  • Cancer cells ignore density-dependent factors that typically curtail cell division.

  • They disregard normal control mechanisms (e.g., cell cycle checkpoints).

Diagnosis and Treatment of Cancer

• Biopsy: Surgical removal of tissue samples to diagnose the presence of cancer.

• Surgical Removal: If benign, they may be removed; if malignant, surgery depends on location and sensitivity.

• Radiation Therapy: Zapping tumors with X-rays to destroy cells.

• Chemotherapy:

  • Uses chemicals that target rapidly dividing cells, impacting both cancerous and healthy cells.

  • Generally has harmful side effects due to cell damage throughout the body.

DNA Replication Basics

• Occurrence: Happens in the nucleus during the S phase of interphase, prior to cell division (mitosis/meiosis).

• Types of DNA: Chromatin form of DNA is used.

Key Enzymes in DNA Replication

• DNA Helicase: Unwinds and separates DNA strands.

• DNA Polymerase: Adds nucleotides to the growing strand; also proofreads newly synthesized DNA to minimize mutations.

• DNA Ligase: Repairs breaks in the sugar-phosphate backbone, reattaching segments as needed.

Steps of DNA Replication

1. Unwinding: Initiated by helicase.

2. Strand Separation: Helicase breaks hydrogen bonds between bases.

3. Nucleotide Addition: DNA polymerase adds new nucleotides to each strand.

4. Proofreading: Checks for errors and repairs them to prevent mutations.

Considerations for DNA replication

• Semi-Conservative Replication: Each new strand consists of one old and one new strand.

• Chromosome Count Post S-Phase: 46 chromosomes doubled, totaling 92 chromatids (not unique).

Key Concepts in Transcription

• Definition: Process to copy a specific segment of DNA into mRNA.

• Location: Takes place in the nucleus.

• Enzyme Involved: RNA polymerase unwinds and transcribes DNA into mRNA.

• Purpose: mRNA synthesized carries the code for protein synthesis.

Translation Process Overview

• Definition: Process wherein ribosomes synthesize proteins based on mRNA sequences.

• Codons: Three-base pairs on mRNA that specify amino acids.

• tRNA: Transfer RNA brings corresponding amino acids based on codon sequence.

• Mechanism:

  • Ribosomes read mRNA; tRNA matching anticodon delivers appropriate amino acid.

  • Peptide bonds form between amino acids to create polypeptide chains.

  • Stops when a stop codon is reached, ending translation.

Mutations in DNA

• Definition: Errors in DNA sequence due to replication mistakes.

• Types of Mutations:

  • Substitutions: One base pair substituted for another.

  • Insertions/Deletions: Adding or removing base pairs, causing reading frame shifts.

• Effects:

  • Can be silent (no effect), missense (changes amino acid), or nonsense (premature stop codon).

  • Not all mutations are harmful; some may confer advantages or be neutral.