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Anatomy Chapter 4a

Terms in this set (50)

Plasma membrane
Separates internal contents of cell from external environment
Nucleus
- Enclosed by a nuclear envelope
Contains the genetic material, DNA
Cytoplasm
Includes cytosol, organelles, and inclusions
Organelles
- Organized structures within cells
Membrane-bound organelles
Non-membrane-bound organelles
Membrane-bound organelles
enclosed by a membrane
e.g., endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria
Non-membrane-bound organelles
not enclosed within a membrane
e.g., ribosomes, cytoskeleton, centrosome, proteasomes
Inclusions
Large diverse group of molecules not bound by membrane
e.g., pigments, glycogen, triglycerides
Endoplasmic Reticulum (ER)
Extends from nuclear envelope to plasma membrane
-Point of attachment for ribosomes
-with ribosomes = rough ER
-without ribosomes = smooth ER
-Point for insertion of enzymes
Functions of Endoplasmic Reticulum
1. Synthesis
-Rough ER synthesizes proteins
-Smooth ER is the site of lipid synthesis & carbohydrate metabolism
2. Transport
3. Packaging and storage
4. Detoxification
5. Structure formation
Golgi Apparatus
-Composed of several elongated, saclike membranous structures - cistern
-"warehouse" of the cell
-Exhibits polarity:
- cisface = closer to ER, receiving region
-trasface = farther from ER, shipping region
Functions of Golgi
-Modification, packaging, and sorting of proteins
-Transport of material from cis-face to trans-face
-Formation of secretory vesicles and lysosomes
Lysosomes
-Small, membranous sacs
-Contain digestive enzymes formed by Golgi
-Participate in digestion of unneeded substances
-Digest contents of endocytosed vesicles
Functions of Lysosomes
Digestion: Digest materials in vesicles that enter cell by endocytosis, remove damaged organelles and cellular components (autophagy), and break down cellular components following cellular death (autolysis)
Peroxisomes
-Membrane-enclosed sacs smaller than lysosomes
-Pinched off vesicles from rough ER
-Contain oxidative enzymes
-Serve in detoxification
--produce hydrogen peroxide
--used to oxidize other substances
-Engage in beta oxidation of fatty acid
--broken down to acetyl CoA
Functions of Peroxisomes
1. Detoxification
2. Beta oxidation
Mitochondria
-Oblong shaped organelles with double membrane
-Contain genes for producing mitochondrial proteins
-Engage in aerobic cellular respiration
-Complete digestion of fuel molecules to synthesize ATP
-Termed "powerhouses" of the cell
-Increase through fission
Function of Mitochondria
Energy harvesting: Digest organic molecules (e.g., glucose) to produce ATP by aerobic cellular respiration; called the "powerhouse" of the cell
Ribosomes
-Contain protein and ribonucleic acid
-Arranged into large and small subunit
-Made within nucleolus and assembled in cytoplasm
-Bound ribosomes attached to external surface of ER membrane
-proteins for plasma membrane, export, or lysosomes synthesized here
-Free ribosomes suspended within cytosol
-all other proteins within cell synthesized here
Functions of Ribosomes
Protein synthesis:
1. Bound ribosomes synthesize proteins destined to be incorporated into the plasma membrane, exported from the cell, or housed within lysosomes
2. Free ribosomes synthesize proteins for use within the cell
Cytoskeleton
-Extends through interior of cell
-Anchors to proteins in plasma membrane
-Includes microfilaments, intermediate filaments, microtubules
Functions of Cytoskeleton
1. Structural support and organization of cell:
Maintains cell shape; protein support of microvilli, cilia, and flagella; stabilizes cell junctions; organizes organelles
2. Cell division: Separates chromosomes during cell
division; splits cell into two daughter cells (cytokinesis)
3. Movement: Facilitates cytoplasmic streaming; involved in movement of vesicles within a cell; participates in muscle contraction
Centrosome
-Usually in close proximity to nucleus
-Contains pair of perpendicularly oriented cylindrical centrioles
-Surrounded by protein
Proteasomes
-Large, barrel-shaped protein complexes
-Located in cytosol and cell nucleus
-Degrade cell proteins through ATP-dependent pathway
Ex. damaged proteins, incorrectly folded proteins, proteins no longer needed
Functions of Centrosomes and Centrioles
1. Organization: Arranges microtubules (proteins of cytoskeleton) and supports their growth in nondividing cells
2. Cell division: Directs formation of mitotic spindle in dividing cells
Functions of Proteasomes
1. Protein digestion: Degrades proteins that are damaged, incorrectly folded, or those that are no longer needed
2. Quality assurance: Controls the quality of exported cell proteins
Cilia and Flagella
-Projections extending from the cell
-Contain both cytoplasm and microtubule proteins
-Enclosed in plasma membrane
-Cilia - Usually found on exposed surfaces of specific cells
E.g., those lining portions of respiratory tract
-Flagella - Longer than cilia, usually appear alone
-Helps propel an entire cell, in humans, only example is sperm cell
Microvilli
-Microscopic extensions from surface of plasma membrane
-Much smaller than cilia
-More densely packed, lack powered movement
-Supported by microfilaments
-Form extensive plasma membrane surface
e.g., in cells of small intestine
increased surface area needed to absorb nutrients
Tight Junctions
-Also termed zonula occludens
-Completely attach cells to neighbors
-Prevent substances passing between epithelial cells
e.g., in small intestine - prevent digestive enzymes from moving between cells
e.g., in urinary bladder - prevention of urine exiting through urinary wall
Desmosomes
-Also termed macula adherens
-Are like snaps between adjacent cells
-Hold cells together at a single point
-Found in cells exposed to stress
e.g., external layer of skin
Hemidesmosomes
Anchor basal layer of cells of epidermis to underlying components
Gap Junctions
-Formed across intercellular space between cells
-Gap bridged by proteins called connexons
-Form tiny, fluid-filled tunnels
-Provide direct passageway for substances to travel between cells
e.g., flow of ions between cells in cardiac muscle
Structure of the Nucleus
-The nucleus is the largest structure in the cell - "control center"
-Typically only one per cell
exceptions: erythrocytes with no nuclei; skeletal cells with many nuclei
Nuclear envelope
-Double phospholipid membrane enclosing nucleus
-Separates cytoplasm from nucleoplasm
-Externally continuous with rough ER
-Contains nuclear pores
-allow passage of large particles, ions, water soluble molecules in and out of nucleus
Nucleolus
-Dark-staining, spherical body, not membrane bound
-Composed of protein and RNA
-Produces small and large ribosome subunits
DNA
-Housed in nucleus
-Composed of repeated monomers (nucleotides)
-Each deoxyribonucleotide composed of :
five-carbon sugar deoxyribose
phosphate
one of four nitrogenous bases:
adenine, cytosine, guanine, and thymine
-Linked through phosphate groups by phosphodiester bonds
-Each molecule with two complementary strands of nucleotides
DNA Packaging
-Wound around nuclear proteins, histones
-together form nucleosomes
-In loose form when not dividing - chromatin
-In tightly coiled form when dividing - chromosomes
Function of the Nucleus
-Cellular regulation: Houses DNA molecules that serve as the genetic instructions for synthesis of proteins
-Production: Produces ribosomal subunits in nucleolus and exports them into cytoplasm for assembly into ribosomes
-Transcription - Ribonucleic acid copy of a gene formed from DNA in the nucleus
-Translation - Uses RNA for synthesis of protein by ribosomes in cytoplasm
General Functions of Cell
-Functions performed by most cells:
-Maintain integrity and shape of cell
-dependent on plasma membrane and internal contents
-Obtain nutrients and form chemical building blocks
-harvest energy for survival
-Dispose of wastes
-avoid accumulation disrupting cellular activities
-Performed by some cells:
-Cell division
make more cells of the same type,help maintain the tissue by providing new cells
Cholesterol
-Scattered within phospholipid bilayer
-Strengthens the membrane
-Stabilizes the membrane against temperature extremes
Glycolipids
-Lipids with attached carbohydrate groups
-Located on outer phospholipid region only
-Helps to form the glycocalyx
the "coating of sugar" on cell's surface
Functions of Plasma Membrane
1. Physical barrier: Establishes a flexible boundary, protects cellular contents, and supports cell structure. Phospholipid bilayer separates substances inside and outside the cell
2. Selective permeability: Regulates entry and exit of ions, nutrients, and waste molecules through the membrane
3. Electrochemical gradients: Establishes and maintains an electrical charge difference across the plasma membrane
4. Communication: Contains receptors that recognize and respond to molecular signals
Plasma Membrane: Membrane Proteins
-Membrane proteins compose half of the plasma membrane by weight
-Can "float" and move about in the fluid bilayer
-Most of a membrane's functions are determined by its resident proteins
-They are classified as integral or peripheral proteins
Integral proteins
-Embedded within and extend across lipid bilayer
-Hydrophobic regions interacting with hydrophobic interior
-Hydrophilic regions interacting with hydrophilic regions
-Often glycoproteins with carbohydrate portion
Peripheral proteins
-Not embedded in lipid bilayer
-Attach loosely to surfaces of the membrane
Transport Proteins
-Regulate movement of substances across membrane
Ex. channels, carriers, and pumps
Cell Surface Receptors
-Bind ligand molecules released from a specific cell
-Bind receptors on another cell
Ex. neurotransmitters and hormones
Identity Markers
-Communicate to other cells
Ex. immune system cells distinguishing healthy cells from foreign cells
Enzymes
-Catalyze chemical reactions
-Globular proteins
-Lower the activation energy of a reaction
-Regulate chemical reactions
Anchoring Sites
Secure cytoskeleton to plasma membrane
Cell-adhesion Proteins
Perform cell to cell attachments
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