Cell Cycle Quiz: Interphase and Mitosis

Course Details

• Course title: The Human Body PJ1311
• Topic: The Cell Cycle and its Control
• Lecturer: Dr Lamia Kandil
• Lecturer of Pharmacy Practice, PhD, FHEA
• MB138
• Email: [email protected]
• vevox.app ID: 102-353-245

Kandil Lectures

• 3 lectures on Genomics
  • Introduction to Genomics
  • The central dogma of life (Transcription, Translation)
  • Cell cycle and control mechanism

The Cell Cycle

• All cells are derived from pre-existing cells
• Cell cycle: ordered series of events preparing for cell division
• Functions of the cell cycle
  • Copying cellular components & DNA duplication
  • Dividing the cell evenly into daughter cells
• "Cell cycle": alternating "growth" and "division" of the cell.
• Cell division is a part of the cell cycle.

Why Cell Division Occurs

• In unicellular organisms, division of one cell reproduces the entire organism (reproduction)
• Multicellular organisms depend on cell division for
  • Growth (increase in numbers)
  • Maintaining and repairing cells (e.g., liver, skin)
• Not all cells divide
  • Some cells can't divide (e.g., eye lens, nerve, heart cells). These cells are maintained.

Cell Cycle Basic Function

• "Growth" activity corresponds to "Interphase"
• Cell growth and copying of chromosomes in preparation for cell division (mitosis and cytokinesis)
• "Division" activity corresponds to "M phase"

Stages of the Cell Cycle

• Interphase (G1, S, G2)
  • G1: Cell growth, normal cell function, organelle duplication, proteins synthesis. G1 checkpoint
  • S: DNA replication
  • G2: Continued growth, organelles and proteins synthesis. G2 checkpoint
• Mitosis (prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis)
  • Prophase: Chromosomes condense, nuclear membrane breaks down, spindle forms
  • Prometaphase: Chromosomes attach to spindle microtubules. Nuclear envelope fragments
  • Metaphase: Chromosomes align at the metaphase plate
  • Anaphase: Sister chromatids separate and move to opposite poles
  • Telophase: Chromosomes decondense, nuclear envelopes reform.
  • Cytokinesis: Cytoplasm divides, producing two daughter cells. Note: Mitosis doesn't include cytokinesis

Interphase Details

• Interphase: about 90% of the cell cycle
  • G1 phase: First gap, cell growth
  • S phase: Synthesis, DNA replication (longest phase)
  • G2 phase: Second gap, cell prepares to divide

G1 Phase Details

• First stage of cell growth after cell replication occurs.
• Preparation of chromosomes for replication
• Duplication of cellular components (cytoplasm and organelles).
• Cell carries out its usual metabolic activities
• G1 checkpoint (restriction point): Cell commits to division or exits from the cell cycle.

S Phase Details

• Instructions for making cell parts are encoded in DNA
• Each new cell needs a complete set of DNA molecules
• DNA must be copied (replicated) before cell division.

DNA Replication

• DNA replication is semiconservative.
• Watson and Crick base pairing is maintained during replication.
• Synthesis of new DNA strands occurs in the 5' to 3' direction.
• DNA replication is a multi-enzymatic process initiated when a primer is required. Several enzymes and proteins (Replisome) are involved in the initiation process.
• Enzymes involved in DNA replication: - Helicase, Binding protein, Primase, DNA polymerase, DNA polymerase I, Ligase
• Replication of DNA: Base pairing allows each strand to serve as a template for a new strand.

Stages of DNA Replication

• The initiation phase
• Elongation phase (Leading and Lagging strand synthesis)
• Termination phase

S Phase - Duplicated Chromosomes

• Duplicated chromosomes are called chromatids
• Chromatids are held together by a centromere

S Phase - Centrosome Duplication

• Centrosome is near the nucleus in animal cell
• Contains microtubule organizing center (MTOC) and two centrioles
• Protein surrounding centrioles that migrate to poles before cell division.

Mitosis

• Mitosis: process separating chromosomes in the cell nucleus into two identical sets in two nuclei
• During mitosis, pairs of chromosomes condense.
• Sister chromatids attach to fibers that pull them to opposite sides of the cell.
• Cytokinesis follows mitosis.

Phases of Mitosis

• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis

Prometaphase (Late Prophase)

• Nuclear membrane and nucleolus break down
• Chromosomes continue condensing and become clearly visible
• Spindle fibers attach to the chromosomes at the centromere

Telophase

• Prophase is essentially reversed.
• Sister chromatids are at opposite poles
• Nuclear envelope forms around each set of sister chromatids and chromosomes condense
• Nucleolus reappears and interphase cellular functions resume

Cytokinesis

• Cytoplasm division
• Divides the cell into two daughter cells (cytoplasm, organelles)
• Cytokinesis begins in telophase and ends shortly thereafter (part of M phase but not mitosis)

Daughter Cells of Mitosis

• Have the same number of chromosomes as the parent cell.
• Identical to each other
• Must grow in size (G1 of Interphase) to become mature
• Ready to enter a new cell cycle

Cell Cycle Control System

• The sequential events of the cell cycle are controlled by a cell cycle control system, similar to a clock
• Controlled by internal and external controls
• Checkpoints in the clock where the cell cycle stops until a go-ahead signal is received.

Cancer Cells

• Cancer cells do not respond normally to the body's control mechanisms.
• They may not need growth factors to grow and divide
• They may make their own growth factors
• They may convey a growth factor's signal without the presence of the growth factor
• May have an abnormal cell cycle control system

Cyclins and Cyclin-Dependent Kinases (Cdks)

• Cyclins: family of proteins activating cyclin-dependent kinase (Cdk) enzymes. Examples: Cyclin A, Cyclin B, Cyclin D, Cyclin E
• Cyclin-Dependent Kinases (Cdks): Family of protein kinases regulating cell cycle, including cdk1, cdk2, cdk4, cdk6
• Maturation Promoting Factor (MPF): Heterodimeric protein composed of cyclin B & cyclin-dependent kinase (CDK1), promoting entrance into mitosis (M phase) from G2 phase, phosphorylating multiple proteins needed during mitosis.

Important Videos (URLs)

• List of URLs for videos provided for further learning.

Important Cell Cycle Checkpoints

• G1 checkpoint: Cell growth, DNA damage, adequate resources.
• G2 checkpoint: DNA replication, damage.
• M checkpoint (spindle checkpoint): Ensures all chromosomes are properly attached to the spindle fibers in metaphase before anaphase.

Purpose of Cell Cycle in Eukaryotic Cells

• Main purpose: Cell division. Additional minor purposes are DNA replication and cell growth.

Phase of Cell Cycle and DNA Replication

• S phase is responsible for DNA replication.

Phase of Cell Cycle and Chromosome Condensation and Breakdown of Nuclear Envelope

• Prophase is the stage where chromosomes condense, and the nuclear envelope breaks down.

Molecule Responsible for Driving Cell Cycle Progression

• CDK (Cyclin-Dependent Kinase) phosphorylates target proteins.

G2 Checkpoint Function

• Checks for DNA damage and repairs it. This checkpoint ensures the cell only goes into mitosis if DNA is undamaged and properly replicated.

Cancer and Normal Cell Cycle Control

• In cancer, the normal control mechanisms of the cell cycle are lost or disrupted.