Download ANPS 019 Beneyto-Santonja 08-31

ANPS 019 08/31/12 Beneyto
Cell Structure  Text Readings: Chapter 3
The cell is the smallest living unit
 Cell components are built with proteins, carbohydrates, lipids, and nucleic acids
 Cells are the building blocks of all plants and animals
 Cells are produced by the division of preexisting cells
 Cells are the smallest units that perform all vital physiological functions
o Obtain food
o Grow
o Reproduce
o Respond to environment
Cell Biology
 Cytology: the study of the structure and function of cells
 The human body contains
o Somatic (body) cells
o Sex cells (sperm/eggs)
 Human cells are diverse in shape and function
A typical cell
 Is surrounded by extracellular fluid, which is the interstitial fluid of the tissue
o Extracellular fluid = interstitial fluid
 Has an outer boundary called the cell membrane or plasma membrane
 Has intracellular fluid within the cell
The Cell Membrane
 The cell membrane is a phospholipid bilayer with proteins, lipids, and carbohydrates
 Physical isolation – separates cell from environment
 Regulation of exchange with the environment
 Structural support of cell
Phospholipid molecules give the cell membrane its structure
 Bilayer: Two sheets of phospholipid molecules arranged with fatty acid “tails” facing
each other
 Hydrophobic interior of bilayer
 Phosphate-containing head provides hydrophilic inner and outer membrane surface
 Membrane proteins give the cell its unique function
o Classified as either
 Intergral Proteins (embedded in membrane)
 Peripheral Proteins (bound to inner or outer surface)
All proteins are amino acid chains that have bent, twisted and/or folded into unique shapes
 With proteins lengths of 100,000 amino acids, the variety of shapes is unlimited
 Transmembrane protein chains always have nonpolar regions associated with the
hydrophobic fatty acid portion of the membrane, and polar or charged areas facing the
intra- or extracellular fluid
Carbohydrates are also associated with the membrane  form the Glycocalyx
 Extend away from cell surface
o Lubricate and protect
o Anchor cell
o Bind extracellular compounds
o Recognized by immune system cells in their search for foreign
o Include proteoglycans, glycolipids, glycoproteins
The Fluid-Mosaic membrane model
 The cell membrane is not a fixed entity
 Lipids move around with respect to their neighbors
 Proteins move around, are added and removed as needed to alter cell function
 The plasma membrane (the outer boundary of the cell) is only one membrane associated
with the cell.
 Numerous structures within the cell, including the nucleus and several organelles, also
have a membrane component.
The nucleus is the center or cellular operations
 Surrounded by a nuclear envelope
o “double membrane” = two phospholipid bilayers
 Communicates with cytoplasm through nuclear pores
 The contents of the nucleus
o A supportive nuclear matrix (nucleoplasm)
o DNA and related proteins
 Chromosomes are the form of DNA when it is tightly packed with
histone proteins into structures visible at the time of cell division
 Chromatin is the uncoiled, loose form of DNA present the rest of the
time, when a cell is in the active, non-dividing state
o One or more nucleoli
 Active areas within DNA, dark cluster or ‘spot;’ indicative of active
protein synthesis
DNA – Chromosome vs. chromatin
 Same idea in different arrangements
The interior of the cell contains:
 Nucleus
 Intracellular Fluid (cytosol)
 Organelles
o Nonmembranous organelles not enclosed by a membrane (include cytoskeleton,
centrioles, ribosomes)
o Membranous organelles are surrounded by phospholipid membranes (include
endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria)
The Cytoskeleton: the structural support network within the cell
 Microfilaments: Smallest; weblike arrangement inside the plasma membrane (actin); help
in cell movement and support
 Intermediate filaments: Strong, resist mechanical stress to cell, stabilize the position of
organelles within cytoplasm
 Microtubules: Largest; long and hollow; provide strength and rigidity to cell; anchored in
centrosome; chromosome movement
 Centrioles are intimately involved with the cytoskeleton
o Organize the cytoskeleton
o Cytoplasm surrounding the centrioles is the centrosome
o Microtubule structure, anchors with microtubules of cytoskeleton
o Direct the movement of chromosomes during cell division