Download Chapter 4 Summary 2401

SUBJECT: ANATOMY & PHYSIOLOGY
BIOL 2401
Chapter 4
Cells
1.
Overview of Cellular Basis of Life
A. The CELL is the basic unit of ALL living organisms. ALL cells come from pre-
existing cells. The Cell Theory - Schleiden and Schwann. The study of cells is
cytology !
B. A cell is mostly composed of 4 elements: C, H, O, and N plus many trace
elements. Living after contains usually over 60% water. The major building
material of cells is protein (chapter 2).
C. Cells vary in size from microscopic (bacteria) to over a meter in length (skeletal
muscle cell). The shape of a cell often defines function. Examples: squamous protection or absorption, or muscle cells are long and cylindrical to allow for
shortening (contraction).
2.
Microscopy – How Cells are Studied !
A. Light Microscopy (uses photons- light)
i.
Bright-field, Dark-field, Phase Contrast, Fluorescence, and Confocal
Fluorescence.
ii. Most give a 2 D image but confocal gives a 3 D image.
iii. ALL limited to a maximum resolution of 0.2µ.
B. Electron microscopy (uses electrons with shorter wavelength)
i.
TEM, SEM STM, AF, CET. More give a 3 D image.
ii. Resolution to the atomic level !!
2. Anatomy of a Generalized Cell : ( review Figure 3.4 and Table 3.1)
A cell has 3 major regions: the nucleus, cytoplasm, and cell (plasma) membrane.
A. The nucleus, or control center, directs most cell activity and is necessary for
reproduction. The nucleus contains genetic material (DNA) which carries
instructions for the synthesis of proteins. Note: only one other organelle contains
DNA and that is the mitochondrion. Has a double membrane.
B. The plasma membrane (PM) encloses the cytoplasm and acts as a selective
barrier to control the movement of most substances into or out of the cell. The
PM is composed of a lipid bilayer (phospholipids) and contains proteins
imbedded in it. Many of these proteins act as enzymes or carriers in membrane
transport, form membrane channels, provide receptor sites for hormones and
other chemical messengers, or play a role in cellular recognition (during
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DR. DAVID L. COX
SUBJECT: ANATOMY & PHYSIOLOGY
BIOL 2401
development and in immune reactions). Specialization of the PM include
microvilli to increase surface area for absorption and cell junctions
(desmosomes, tight, and gap junctions).
C. The cytoplasm is where most cellular activities occur. It’s fund substance, the
cytosol, contains inclusions (stored minerals and food sources) and specialized
bodies called “organelles” (little organs), each with a specific function. For
example mitochondria make ATP, ribosomes make proteins, and Golgi apparatus
package protein for secretion. Lysosomes carry out intracellular digestion, and
peroxisomes destroy dangerous chemicals that might e toxic. The cytoskeleton
function in cell support and motion. The centrioles play a role in cell division and
form the core of flagella and cilia.
3.
Cell “Life Functions”
A. Maintain shape and boundaries (control flow in and out of cell)
B. Obtain nutrients (glucose, amino acids, fats, minerals, etc.)
C. Dispose wastes (acids, CO2, urea, etc)
D. Growth (make new components, replace old ones, increase size, etc)
E. Divide (make new cells to replace dead or dying ones)
4.
The Plasma Membrane
A. Made of lipids and protein. Fluid Mosaic Model.
B. Bilayer of phospholipids is a barrier to most chemicals.
C. Phospholipids have polar (hydrophilic) head and non-polar (hydrophobic) tails.
D. Membrane proteins “float” in sea of phospholipids.
i.
Integral proteins go through both layers of phospholipids
ii. Peripheral proteins attached to only 1 leaflet.
iii. Usually transport proteins, cell surface receptors /markers, or anchoring /
adhesion proteins.
E. Membrane Transport
i.
Passive Processes:
a. Diffusion - movement of substance from a high to low concentration. Due
to the kinetic energy in molecules.
b. Osmosis - diffusion across a semipermeable membrane.
c. Facilitated diffusion – requires a protein channel or carrier. Glucose is
commonly transported into the cell by this mechanism.
d. Filtration is the movement of substances through a membrane from an
area of high hydrostatic pressure to an area of lower fluid pressure. In the
body, the driving force of filtration is blood pressure.
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DR. DAVID L. COX
SUBJECT: ANATOMY & PHYSIOLOGY
BIOL 2401
ii. Osmotic pressure - reflects the solute concentration of a solution, and
determines whether cells gain or lose water.
a. Hypertonic solutions contain more solutes (and therefore less water)
than do cells in these solutions, cells lose water by osmosis and shrink
(crenate).
b. Hypotonic solutions contain fewer solutes (and therefore more water)
than do the cells in these solutions, sells well and may rupture (lyse) as
water rushes in by osmosis.
c. Isotonic solutions, will have the same solute to solvent ratio as cells, and
thus cause no change in the cell shape or size. (0.9% or 0.15M NaCl)
iii. Active processes (Active transport and vesicular transport): requires ATP
a. In active transport, substances are moved across the membrane against
an electrical or concentration gradient by proteins called solute pumps.
This accounts for the transport of amino acids, some sugars, and most
ions. The sodium-potassium pump is the best example and is key to the
function of many cells, especially neurons and muscle cells.
b. The two types of ATP activated vesicular transport are exocytosis and
endocytosis. Exocytosis moves secretions and other substances out of
cells; a membrane-bound vesicle fuses with the PM ruptures, and ejects
its contents to the cell exterior. Endocytosis, and which particles are
taken up by enclosing enclosure in a plasma membrane sac include
phagocytosis (cell eating) and pinocytosis (cell drinking). A highly
selective endocytosis is called receptor-mediated endocytosis in which
membrane receptors bind with an internalized only selected target
molecules such as hormones, and other chemical messengers.
F. Cell to Cell Communication
A. Cells must communicate in an organ, organ system, or body to function.
B. Do so through ligands (soluble chemicals)
i. Channel linked receptors
a. Permit ion passage through membrane channel proteins. Gates
opened by ligands. ex. Acetylcholine in nerve conduction.
ii. Enzymatic receptors
a. Ligand binds to receptors and activates membrane enzymes inside the
cell.
iii. G-protein receptors
a. Indirectly activate GTP proteins which may activate protein kinases or
2nd messengers inside the cell.
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DR. DAVID L. COX
SUBJECT: ANATOMY & PHYSIOLOGY
BIOL 2401
5. Organelles
A. Endoplasmic Reticulum (ER) - network of concentric membranes surrounding
the nucleus. Some ER contains ribosomes (rough ER or RER) for synthesizing
proteins. RER also forms transport vesicles containing proteins that migrate to
the Golgi apparatus for processing and storage.Other ER lack ribosomes
(smooth ER or SER) and are involved in lipid synthesis. SER are also involved in
peroxisome formation and the detoxification of poisons.
B. Golgi Apparatus - these are the “warehouse of the cell” where proteins are
processed, sorted, and stored. They look like a stack of pancakes. Transport
vesicles enter the cis face and progress from one sac to another until they reach
the trans face and are either stored or released.
C. Lysosomes - round membranous organelles that contain digestive enzymes.
Used to destroy and recycle old organelles, as well as digest foreign particles.
D. Peroxisomes - smaller, round membranous organelles that contain peroxide.
Used for detoxification and beta-oxidation (breakdown of fats).
E. Mitochondria - the “powerhouse of the cell”. Provides most of the energy (ATP)
for the cell. Kreb’s cycle and electron transport occur here. Has a double
membrane
F. Ribosomes - small non-membranous organelles that are involved in translation
(protein synthesis). Consist of a small and large subunit. Some are free in the
cytoplasm and some are bound (RER).
G. Cytoskeleton - proteinaceous skeleton made from 3 components.
I. Microfilaments - smallest component; thin, flexible. example actin.
II. Intermediate filaments - larger, more rigid filaments; ex. keratin.
III. Microtubules - largest component, form the backbone of the cytoskeleton
with the other 2 filaments running between them like latticework.
H. Centrosome - non-membranous organelle close to the nucleus that contains 2
centrioles made from 9 groups of microtubules. Plays a central role in cell
division as well as the formation of flagella and cilia.
I. Proteasome - non-membranous organelles that digest old or unneeded proteins.
J. Cilia and Flagella - external structures used for motility. Cells may have 100s of
cilia, but usually only 1 flagella. Flagella core is made of microtubules.
K. Microvilli - external folds in the cell membrane used for absorption. Core maed
of actin filaments.
L. Cell membrane junctions - connect adjoining cells.
I. Tight junctions - hold cells together in a single layer. Structure is like a ziplock zipper. Prevents liquid from passing between cells.
II. Desmosomes - junctions that hold cells together like a snap or rivet.
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DR. DAVID L. COX
SUBJECT: ANATOMY & PHYSIOLOGY
BIOL 2401
III. Gap junctions - junctions which allow ions, water, and nutrients to pass from
one cell to the next.
M. Nucleus - control center of the cell. Controls all cell activity except that of
mitochondria. Surrounded by a double membrane that contains nuclear pores.
I. Nucleoplasm - material inside nucleus. Made of DNA and protein
(chromatin).
II. Nucleolus - region of nucleus where ribosomes components are synthesized.
The components are transported to the cytoplasm for assembly.
6. Cell Genetics
A. Transcription - the genetic information in a gene is used to synthesize a
molecule of messenger RNA (mRNA). RNA polymerase carries out this function
by reading bases on the DNA molecule and placing a complementary base on
the growing mRNA strand.
I. Introns - part of the mRNA code that is cut out and discarded.
II. Exons - part of the mRNA code that is spliced together and expressed.
III. A gene is a segment of DNA that carries the instructions for building one
protein. The information is in the sequence of bases in the nucleotide strands.
Each three base sequence (triplet) specifies one amino acid in the protein.
IV. The transfer of genetic information from DNA to RNA is called transcription.
This occurs in the nucleus of the cell.
B. Translation - Protein Synthesis - Involves both RNA and ribosomes.
I.
Messenger RNA (m-RNA) carries the instructions for protein synthesis from
the DNA (gene) to the ribosomes. The triplet sequences on a molecule of
mRNA are called codons. Transfer RNA (t-RNA) transports amino acids to
the ribosomes. Complimentary triplet sequences on a molecule of tRNA are
called anti-codons. Ribosomal RNA (r-RNA) forms part of the ribosomal
structure and helps coordinate the protein building process. The codons and
anti-codons must match in the ribosome in order for protein synthesis
(translation) to occur.
II. The transfer of genetic information from RNA to protein is called translation.
This occurs either in the rough endoplasmic reticulum (RER) or on free
ribosomes in the cytoplasm.
C. The Cell Cycle - the process of cell growth and division.
I. Interphase - made of 3 phases. Cells spend most of the time here.
a. G1 - cells grow, produce new organelles, ad develop.
b. S - cells replicate (copy) all their DNA (genes).
c. G2 - growth, production of enzymes for mitosis,centrioles divide.
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DR. DAVID L. COX
SUBJECT: ANATOMY & PHYSIOLOGY
BIOL 2401
II. Mitosis - Cell division – two phases, mitosis (nuclear division) and
cytokinesis (division of the cytoplasm).
a. Mitosis begins after DNA has been replicated (during interphase); it
consists of four stages. The result is two daughter nuclei, each identical to
the mother nucleus.
1. Prophase - nuclear envelope breaks down; chromosomes become
visible.
2. Metaphase - all chromosomes align on the equatorial plane. Centriole
spindle fibers attach to each sister chromatid.
3. Anaphase - centrioles pull the sister chromatids apart towards the
poles of the cell.
4. Telophase - the chromosomes unwind and disappear. A membrane
begins to form between along the equatorial plane. The nuclear
envelope begins to reform.
b. Cytokinesis usually begins during anaphase and progressively pinches
the cytoplasm in half. Cytokinesis this not always occur ; in such cases of
bi- or multi-nucleated cell result.
c. Mitotic cell division provides an increased number of cells for growth and
repair.
Organelle
cell membrane
microvilli
cilia, flagella
cytoplasm
nucleus
nucleolus
centrosome
rough ER
smooth ER
ribosome
Golgi apparatus
mitochondrion
peroxisome
lysosome
inclusions
vesicles
cytoskeleton
proteasome
Function
Stages of Mitosis
(PMAT)
Table 4.2
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DR. DAVID L. COX