GENERALIZED ANIMAL CELL
A cell is the basic, living, structural and functional unit of the body.
Cytology is the science concerned with the study of cells.
he principal parts of a cell are the:
Cell (plasma ) membrane - separates inside of cell from external environment.
Nucleus - contains the cell’s DNA and nucleolus.
Cytoplasm -contents of the cell between the nuclear envelope and cell membrane.
cytosol - contains proteins, enzymes, nutrients, ions, and other small molecules.
organelles - highly organized structures with characteristic shapes that are specialized for specific cellular activities.
inclusions - are temporary structures in the cytoplasm that contain secretions and storage products of the cell.
Cell Membrane Structure:
Made primarily of phospholipids and proteins - fluid mosaic model
Lipids:
Phospholipids - form the basic structure of the membrane (bilayer)
Glycolipids - the target of certain bacterial toxins
are important for adhesion among cells
may mediate cell-to-cell recognition and communication
contribute to regulation of cell growth and development.
Cholesterol - strengthen the membrane but decrease flexibility
Proteins:
Determine to a large extent what the cell can do.
Integral proteins : Extend from one side of the membrane to the other.
Channels
Transporters
Receptors
Peripheral proteins: loosely attached to the inside or outside of the cell.
Enzymes
Cell identity markers
Cell Membrane Function:
cellular communication
electrochemical gradient - resulting in a membrane potential
selective permeability -
lipid solubility - nonpolar, hydrophobic molecules can pass size - only a few, small uncharged polar molecules can pass electrical charges - these prevent passage
the presence of channels and transporters
MOVEMENT OF MATERIALS ACROSS PLASMA MEMBRANES Passive Transport : depends on concentration and kinetic energy Diffusion
Facilitated Diffusion
Osmosis
Osmotic Pressure
Tonicity
Isotonic
Hypertonic - crenation
Hypotonic - hemolysis
Active Transport: Primary Active Transport Secondary active transportsymports or cotransport
antiports or countertransport
Vesicular transport
Endocytosis
Pinocytosis
Phagocytosis
Receptor-Mediated Endocytosis
Exocytosis
Transcytosis Organelles Endoplasmic reticulum Smooth E R - Site of lipid synthesis
Detoxification of chemicals
Sarcoplasmic reticulum holds calcium for muscle contractions
Rough E R:
Rough due to the presence of ribosomes
Site of protein sythesis - primarily for export
Proteins are then sent to the Golgi apparatus for processing
made of ribosomal RNA and proteins
"Workbenches" where proteins are put together
Golgi Apparatus Made of flattened membranous sacs or cisternsProcesses proteins and lipids made in the E R
Forms vesicles for transport of proteins
Forms lysosomes and peroxisomes
Lysosomes Tiny, membrane sacs containing digestive enzymesFunction in:
intracellular digestion(phagocytosis, pinocytosis and
receptor- mediated endocytosis)
digestion of worn-out organelles (autophagy), digestion of
cellular contents (autolysis) after death and in some pathological conditions
extracellular digestion of debris at infection site
Peroxisomes
Contain peroxidases which oxidize organic substances and produce H2O2
Synthesize bile salts
Breakdown very long chain fatty acids
Mitochondria
Double membrane - inner membrane has folds called cristae
Cellular respiration - requires oxygenMost of the cell’s ATP is produced by these "powerhouses"
Have unique DNA and RNA’s Cytoskeleton Microfilaments - made of actin - aid in movementMicrotubules - made of tubulin - rigid, helps maintain cell shape
Intermediate filaments - many proteins - structural reinforcement
Centrioles - sets of microtubules at right anglesForm spindle fibers during cell division
Found in cilia and flagella
Cilia
Short, numerous hairlike projections
Contain a modified centriole called a basal body
FlagellaSingle, long projection - found only in sperm in human
VesiclesMembrane sacs used for transport within the cell.
Inclusions Substances produced by the cell NOT surrounded by a membraneUsually temporary
Glycogen, lipids, melanin
Nucleus Enclosed in a double membrane called the nuclear envelopePores in the nuclear envelope allow for large molecules to leave
Contains nucleoplasm.
Chromatin - DNA and histones- chromosomes during cell division
Nucleolus - site of ribosome production
CELL DIVISON
Division of the cytoplasm - CytokinesisNuclear division
mitosis - makes identical copies of somatic cells
meiosis - makes gametes (eggs or sperm) for reproduction
Homologous chromosomes - "matching" chromosomes or members of a pair.
One homolog is received from each parent, and homologous chromosomes carry the same basic information, or genes. The genes may code for different forms of the same trait.
The Cell Cycle
Interphase - "resting stage" - cells are carrying on growth and all the normal functions of the cell.
G1 - Gap 1 or growth phase
S phase - DNA synthesis occurs during this phase.
DNA replication is semiconservative - each half makes a new strand.
Once DNA is duplicated, the cell is committed to division.
G2 - Gap 2
Mitosis - actually one continuous process that we describe in stages:
Prophase :
Chromosomes condense and become visible
Sister chromatids are held together by a centromere
Nucleoli disappear
Mitotic spindle forms
Prometaphase : or late prophase
Nuclear envelope disappears
Spindle fibers attach to kinetochores - protein complexes attached to centromeres.
Metaphase :
Chromosomes line up in the center of the cell at the metaphase plate.
Anaphase :
the centromere of each chromatid pair splits, and the microtubules shorten and pull one of each duplicated chromosome to opposite ends of the cell ensuring each new cell gets a copy of each chromosome.Telophase :
the mitotic spindle disappear
new nuclear membranes form
the nucleoli can be seen again
the chromosomes unwind
Cytokinesis: Begins in anaphase and finishing after telophaseIn anaphase, cells form a contractile ring perpendicular to the axis of the mitotic spindle.
This ring pinches the cell into two, using some of the same proteins used in muscle tissue.
Cell Differentiation - the process where a cell changes from an unspecialized cell to a cell suited for a specific function.
Control of Cell Division
Cells have a "mitotic clock" - they reproduce a certain number of times, then stop
Apoptosis - programmed cell death - DNA breaks up, cytoplasm shrinks, cell is phagocytized (vs. Necrosis)
Controlled by intracellular levels of kinases and cyclins
Cell size
Hormones
Growth factors
Contact inhibition
Loss of Control of Cell Division
Tumor formation
Benign - remains localized
Malignant (cancerous) - spreads into surrounding tissue or metastasizes
Oncogenes - activate other genes which increase cell reproduction rate Tumor suppressor genes - control the rate of cell reproductionGenes may be damaged by:
toxic chemicals
radiation ( including sunlight)
natural mutations
viruses