Chapter3c
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Transcript of Chapter3c
The Cytoskeleton
• A networked mesh of protein rods that support the cell, acting as scaffolding
• Also contain contractile units that allow for the movement of cells and for intracellular movement (organelle movement, vesicular transport)
• Three Types:– Microtubules– Microfilaments– Intermediate filaments
Microfilaments
• Thin (but dense), cross-linked strands of actin (contractile proteins)
• Involved in cell motility and changes in shape
Intermediate Filaments
• Tough, stable, permanent, rope-like protein fibers
• Have high tensile strength
• Helps cells resist mechanical stress and are found in desmosomes for cell-cell contact
Microtubules
• Long, hollow tubes composed of tubulin. Large in diameter
• Radiate from the centrosome
• Determine cell shape and organelle distribution
• Important in intracellular transport
Centrosome & Centrioles
• “microtubule organizing center”
• Composed of two centrioles (90o to each other) and a granular matrix
• Matrix generates microtubules
• Centrioles generate spindle fibers during cell division
Cellular Extensions: Cilia
Cellular Extensions: Flagella
• Sperm cells are the only cells in the human body with flagella
• Similar to cilia but are longer and allow cells to propel themselves
• Use a whip-like motion for locomotion
Cellular Extensions: Microvilli
• Finger-like plasma membrane projections• Increases plasma membrane surface area• Typically found in absorptive cells• Example: Lining of the small intestine
The Nucleus
• The “control center” of the cell containing genetic information
• The largest organelle of
the cell and is filled with nucleoplasm
• Composed of: Nuclear envelope, Nucleolus, and Chromatin
The Nuclear Envelope
• Double membrane barrier separated by a fluid-filled space
• Outer membrane is continuous with RER & is studded with ribosomes
• Inner membrane is lined with nuclear lamina
• Two membranes come together and form nuclear pores (entry and exit point of particles)
Nucleoli
• Small, dense body composed of RNA and protein, where ribosomes are synthesized
Chromatin
• Loosely coiled DNA fibers and histone proteins, condense to form chromosomes.
• DNA + histone = nucleosome
• Condense into chromosomes during cell division
The Cell Cycle
• Cell cycles form a multi-celled organism from one original cell
• A series of changes cells go through from the time they are formed until they divide
• Promote growth and tissue repair in organisms
• Involves phases and checkpoints for quality control
*Movie time!
Interphase• Cell growth and DNA
replication, “preparation period”
• G1 Phase: Growth Phase 1, structures are duplicated
• S Phase: Synthesis Phase, DNA is replicated
• G2 Phase: Growth Phase 2, more structural duplication, final preparations
DNA Replication
• Occurs before cell division• DNA is uncoiled & H-bonds broken by a helicase• DNA polymerase introduces complementary bases• Replicated DNA is semi-conservative• DNA condenses after replication
Mitosis
• Division of the nucleus: – Prophase– Metaphase– Anaphase– Telophase
• Cytokinesis: Division of the cytoplasm
• Exceptions: RBCs, nervous, skeletal & cardiac tissue
Mitosis
Mitosis
Protein Synthesis
• DNA provides the information for protein synthesis
• Two events:– Transcription
– Translation
Transcription
• Synthesis of complementary mRNA (messenger RNA)
• Transcribes the code for making proteins and transports it outside the nucleus
Translation
Translation
• Every mRNA codon corresponds to an amino acid
• Examples: – CAC = Histidine– CAA = Glutamine– AAA = Lysine