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Cell Physiology
Cell:
Basic living unit of structure & function of the body. > 100 trillion cells in body. Very small (10-5 m in diameter). Highly organized. Variety of shapes & sizes. Each type of cells has a special function.
Cell (continued)
All Cells share certain characteristics:
General cell structure & components. General mechanisms for changing nutrients to Energy. Deliver end products into their surrounding fluid. Almost all have the ability to reproduce.
General Cell structure:
The cell has two major compartments: the nucleus & the cytoplasm.
The cytoplasm contains the major cell organelles & a fluid called cytosol.
3 principal parts: Plasma (cell) membrane. Cytoplasm & organelles. Nucleus.
General Cell Structure & FunctionComponentStructureFunction
Plasma (cell) membrane
Membrane composed of double layer of phospholipids in which proteins are embedded
Surrounds, holds cell together & gives its form; controls passage of materials into & out of cell
CytoplasmFluid, jellylike substance b/w cell membrane & nucleus in which organelles are suspended
Serves as matrix substance in which chemical reactions occur.
Nucleus:- Nuclear
envelope
- Nucleolus
- Chromatin
Double-layered membrane that surrounds nucleus, composed of protein & lipid molecules
Dense nonmembranous mass composed of protein & RNA molecules
Fibrous strands composed of protein & DNA
Supports nucleus & controls passage of materials b/w nucleus & cytoplasm
Produces ribosomal RNA for ribosomes
Contains genetic code that determines which proteins (including enzymes) will be manufactured by the cell
Plasma (cell) membrane
Plasma membrane:
Surrounds, holds cell together & gives its form. 75 to 111 Å thickness. Not solid. Separates cell’s internal structures from extracellular
environment. Is selectively permeable, & controls passage of
materials into & out of cell. Participates in intracellular communication.
Plasma (Cell) Membrane
Composed of:
Double layer of phospholipids (hydrophobic/ hydrophilic parts).
Proteins span, or partially span the membrane.
Negatively charged carbohydrates attach to the outer surface.
Plasma Membrane (continued)
General composition of cell membrane
Proteins ……………………. 55% Lipids ……………………….. 41%
- Phospholipids … 25%
- Cholesterol ……. 12% Lipids
- Glycolipids …….. 4%
Carbohydrates …………… 3%
Cell membrane phospholipids
Consists of:
a. Glycerol head that contains phosphate group
(polar & hydrophilic).
b. 2 fatty acid ‘tails’ (nonpolar & hydrophobic).
The hydrophobic parts restricts the passage of H20 & H20- soluble ions.
1. Integral proteins: / Internal or intrinsic proteins
- span the membrane. - transport proteins. - provide structural channels or pores.
2. Peripheral proteins: / external or extrinsic proteins
- embedded in one side (face) of the membrane. - carrier proteins. - bind with substances to be transported. - include hormone receptors & cell surface antigens.
Cell membrane proteins
General functions of cell membrane proteins
1. Provide structural support.2. Transport molecules across the membrane.3. Enzymatic control of chemical reactions at cellular surface.4. Some function as receptors for hormones.5. Some function as regulatory molecules, that arrive
at outer surface of the membrane.6. Some act as antigens and induce the process of
antibody formation.
Cell membrane carbohydrates
Primarily attached to the outer surface of the membrane as:
- Glycoproteins … (most of it).
- Glycolipids …… (1/10).
1. Attach cells to each other.
2. Act as receptor substances.
3. Some enter in immune reactions.
4. Give most of cells overall –ve surface charge, which affects the interaction of regulatory molecules with the membrane.
General functions of cell membrane carbohydrates
Cytoplasm & Organelles
Cytoplasm, Organelles, Nucleoli (continued)
Cytoplasm
The aqueous content of a cell (fluid, jellylike
substance), that lies b/w cell membrane & nucleus
in which organelles are suspended.
Serves as matrix substance in which chemical
reactions occur.
‘cytosol’ is the term used to describe fluid portion of
the cytoplasm.
Organelles (excluding nucleus)
Subcellular structures within the cytoplasm that perform specific functions.
Generalized view of a mammalian cell showing organelles common to all cells (such as the Golgi
complex) as well as specialized structures (e.g., cilia) found only in some cells.
Cytoplasmic Organelles: Structure & Function
ComponentStructureFunction
Endoplasmic reticulum
System of interconnected membrane-forming canals & tubules
Agranular (smooth) ER metabolizes nonpolar compounds & stores Ca2+ in striated muscle cells; granular (rough) ER assists in protein sysnthesis
RibosomesGranular particles composed of protein & RNA
Synthesize proteins
Golgi complexCluster of flattened membranous sacs
Synthesizes carbohydrates & packages molecules for secretion. Secretes lipids & glycoproteins
MitochondriaMembranous sacs w folded inner partitions
Release energy from food molecules & transform energy into usable ATP
LysosomesMembranous sacsDigest foreign molecules & damaged organelles
An illustration of the processing of proteins by the granular endoplasmic reticulum & Golgi complex. Notice the formation of vesicles at the ends of some of the flattened sacs of the Golgi complex.
The endoplasmic reticulum. Agranular ER has ribosomes attached to its surface, whereas granular ER lacks ribosomes.
A model structure of a ribosome. It is composed of two subunits: smaller (lighter) & larger (darker) subunits. The space between the two subunits accommodates a molecule of transfer RNA, needed to bring amino acids to the growing polypeptide chain.
The structure of a mitochondria. The outer mitochondrial membrane & the infoldings of the inner membrane. The fluid in the center is the matrix.
ComponentStructureFunction
PeroxisomesSpherical membranous vesicles
Contain enzymes that detoxify harmful molecules & break down hydrogen peroxide
CentrosomeNonmembranous mass of 2 rodlike centrioles
Helps to organize spindle fibers & distribute chromosomes during mitosis
VacuolesMembranous sacsStore & release various substances within the cytoplasm
Microfilaments & microtubules
Thin, hollow tubesSupport cytoplasm & function as cytoskeleton, transport materials within the cytoplasm
Cilia & flagellaMinute cytoplasmic projections that extend from the cell surface
Move particles along cell surface, or move the cell
Cytoplasmic Organelles: Structure & Function (continued)
The formation of the cytoskeleton by microtubules. Microtubules are also important in the motility (movement) of the cell, & movement of materials within the cell.
Nucleus
Cell Nucleus Is a large spheroid body. Largest of organelles. Contains the genetic material (DNA). Most cells have a single nucleus. Enclosed by inner & outer membrane (nuclear
envelope). Outer membrane is continuous with ER.
Nuclear pore complexes fuse inner & outer membranes together. Selective active transport of proteins & RNA.
Cell Nucleus
(a) The cell nucleus is enclosed in a double membrane called the nuclear envelope. Pores in the envelope permit the passage of molecules in & out of the nucleus. The outer layer of the nuclear envelope is continuous with the endoplasmic reticulum, so that the lumen of the ER is continuous with the perinuclear space. In the nondividing nucleus, DNA is visible as chromatin. The nucleolus plays a role in the synthesis of ribosomes from RNA. (b) A nuclear pore is formed from the fusion of the two layers of the nuclear envelope. Proteins are thought to be located in the pores.
Cell Nucleus (continued)
Nucleoli: Dark areas within the nucleus, not surrounded by
membrane. Centers for production of ribosomes.
Chromatin: Threadlike material that makes up chromosomes.
Intercellular Junctions
Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact
Intercellular junctions facilitate this contact
There are several types of intercellular junctions1.Tight junctions
2.Desmosomes
3 .Gap junctions
Tight Junctions, Desmosomes, and Gap Junctions
-At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid
-Desmosomes (anchoring junctions) fasten cells together into strong sheets
-Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells
Tight junction
0.5 µm
1 µm
Desmosome
Gap junction
Extracellularmatrix
0.1 µm
Plasma membranesof adjacent cells
Spacebetweencells
Gapjunctions
Desmosome
Intermediatefilaments
Tight junction
Tight junctions preventfluid from movingacross a layer of cells