Cell cycle and Mitosis Chap12 Flashcards
Cell division
There are three main types of cell division: Binary fission, which is prokaryotic cell division, Mitosis, which is eukaryotic cell division producing somatic (body) cells (human body cells are diploid), and Meiosis which is eukaryotic cell division producing gametes (sex cells) (gametes are haploid).
Sexual reproduction
Sexual activity (2 parents): two sources of DNA = genetically diverse offspring (under most circumstances), meiosis and fertilization.
Asexual reproduction
No sexual activity (1 parent): one source of DNA = genetically identical offspring, Binary fission, Mitosis
Importance of cell division
Cell division is an important process for reproduction (making more life), fetal development (growth), and tissue repair. Before any cell can divide, it must first replicate (make a copy) of its DNA, so that each daughter cell has a copy of the DNA.
Organization of the DNA in the cell
Genome; complete set of all the cell’s DNA: Genetic material, molecules that determine the inherited traits of an organism (usually DNA). DNA associates with proteins called histones to form units called nucleosomes. Nucleosomes: units of 8 histone proteins at the core with DNA wrapped around it.
Organization of the DNA in the cell (p2)
Nucleosomes in a cell take different forms depending of in the cell is non-dividing or dividing. Chromatin: loosely packed/coiled nucleosomes in non-dividing cells. Chromosomes: tightly packed, highly condensed, nucleosomes in a dividing cell.
DNA Replication produces replicated chromosomes
Before a cell can divide, the DNA MUST be replicated (duplicated/synthesized): DNA Replication: produces an exact copy of all of the DNA in the cell. Converts un-replicated chromosomes into replicated chromosomes with two identical ‘sister’ chromatids. Chromatid: 1/2 of a replicated chromosome joined to another chromatid at the centromere.
Intro-cell cycle
A representation of the events that a cell performs from the moment it is formed to when it divides.
Cell cycle phase 1
Interphase: non dividing phase for cell growth, DNA replication, and production of organelles and enzymes, includes 4 smaller subphases, G0, G1, S, G2.
Cell cycle phase 2
M (mitotic) phase: dividing phase that separates the genetic material while producing multiple cells. M phase = mitosis+ cytokinesis. Mitosis consists of 5 smaller subphases: prophase, prometaphase, metaphase, anaphase, telophase.
Interphase
Interphase is separated into 4 subphases based on specific events that occur inside the cell.
G1 (Growth): cell performs its normal functions, growing and producing organelles, enzymes, and proteins.
Interphase (p2)
S (Synthesis): DNA synthesis / replication producing replicated chromosomes with 2 sister chromatids.
A cytoplasmic protein called the centrosome is also replicated in the S phase.
Interphase (p3)
G2 (Growth): cell continues growth and produces new proteins required for M phase.
G0: a non-dividing phase where cells do not replicate their DNA nor prepare for division.
Centrosomes and mitotic spindles
During s phase cells replicate their DNA and the centrosomes, centrosomes are a cytoplasmic protein complex that forms / organizes the mitotic spindle during mitosis. Mitotic spindle: microtubule proteins of the cytoskeleton that coordinates division of chromosomes
Phases of Mitosis
PRO,PROMETA,META,ANA,TELO
Metaphase = middle phase (use M as a reminder)
Pro = before
Prometaphase = phase right before metaphase
Prophase = before all other phases
A in anaphase = after
Anaphase comes just after metaphase
T in telophase = tail end
Telophase come at the tail end of mitosis
Pro’s
Prophase, loosely coiled chromatin condenses to form distinct chromosomes with sister chromatids linked at the centromere. Prometaphase, referred to as late prophase, nuclear envelope degrades, exposing chromosomes to cytoplasm, mitotic spindle links to chromosomes by attaching to kinetochore proteins in the centromere.
Meta, Ana
Metaphase, mitotic spindles align chromosomes in the middle of the cell in a single file row. Anaphase, sister chromatids are pulled apart towards opposite ends of the cell
Telo
Final step of mitosis, practically the opposite of prophase, chromosomes begin to revert back to its loose, chromatin state. Mitotic spindle degrades, nucleolus and nuclear envelope reform at each end of the cell to form 2 nuclei.
Cytokinesis
Mitosis divides the nucleus but is followed by cytokinesis to produce two identical daughter cells.
Cytokinesis: division of the cytoplasm separating one cell into two cells.
Animal and plant cell cytokinesis differ in their mechanism.
Animal cytokinesis
In animal cells, cytokinesis forms a cleavage furrow
Cleavage furrow: small indentation of actin microfilaments and myosin at the center of a dividing cell.
Plant cell cytokinesis
Recall: unlike animal cells, plant cells are surrounded by a cell wall.
In plant cytokinesis, vesicles from the golgi apparatus carry materials to generate a cell plate and separate each daugter cell.
Cell plate: precursor to the fully developed cell wall.
Cell Cycle regulation
Cell division is controlled / activated by a variety of cellular signals in the form of proteins called growth factors.
Growth factor: a biological substance that promotes cell division.
Also, multiple cell cycle ‘checkpoints’ prevent the cell from entering the next phase prematurely.
If an error is detected at an checkpoint, a protein called p53 can trigger repair or apoptosis (cell death).
A cell that ‘ignores’ cell cycle checkpoints can lead to cancer.
Cell cycle checkpoints
4 major checkpoints control the progress of the cell cycle:
G1 Checkpoint: the cell fixes damaged / mutated DNA in preparation for DNA replication in the S phase.
G2 Checkpoint: ensures all enzymes and proteins needed for mitosis and cytokinesis are available
M Checkpoint: confirms that all chromosomes are aligned and spindle fibers are attached properly
Role of signaling molecules in cell cycle regulation
Signaling molecules and their receptors control the progression through the checkpoints in the cell cycle.
A common signaling molecule is cyclin, which binds to a variety of receptor proteins such as Cdk shown above.
When cyclin binds to Cdk it becomes a molecule called MPF which initiates cell processes that cause the cell to progress to the next stage in the cell cycle.
Cancer
Cancer: a disease characterized by uncontrollable cell division, leading to development of malignant tumors.
Tumors: an overgrowth of cells (an abnormal mass of tissue) that can cause health complications.
Malignant tumors: an overgrowth of cancerous cells that migrate (metastasize) to other organs.
Cancerous
Non-capsulated
Fast growing
Benign tumors: an overgrowth of cells that do not migrate (remain at the same site).
Non-cancerous
Capsulated
Slow growing
Types of genes regulating cell growth
In a healthy, normal cell, 2 types of genes regulate cell growth
Proto-oncogene: provide signals that promote appropriate cell division (green light for cell division)
Tumor-suppressor gene: provide signals to inhibit cell division (red light for cell division)
P53 serves as a tumor suppressor gene
Types of genes regulating cell growth (p2)
Mutations in either of these types of genes can lead to the development of cancer
Though proto-oncogenes are essential, they are s susceptible to mutations that generate oncogenes
Oncogene: mutated gene that promotes unrestrained cell growth (cancer)
