Chapter 3: Cells
Cells: the basic structural & functional units of living
things
-
plasma membrane: flexible outer surface of cell; selective barrier
that regulates flow of materials into & out of cell – maintains
internal environment
-
cytoplasm: all cellular contents between plasma membrane &
nucleus
-
contains organelles: small, membrane-bounded bodies with a specific
structure & function (e.g.: mitochondria, chloroplasts, lysosomes) in cytosol
(semifluid medium between nucleus and
plasma membrane)
-
nucleus: large organelle that stores DNA in the form of chromosomes containing genes
Cell membrane: outer
boundary of cells
-
phospholipid
bilayer: semipermeable and selectively permeable
-
functions in regulation
of passage of molecules into and out of the cell
-
membrane
components:
-
phospholipids: create
bilayer
-
have polar &
nonpolar parts
-
glycolipids:
protective function, and cell identity (specific for cell type)
-
cholesterol: bulky;
controls (reduces) permeability
-
proteins: also glycoproteins; can be transmembrane (spans the entire membrane) or
embedded in either the cytoplasmic or extracellular side of the membrane
-
glycoproteins (and glycolipids) function in cell-cell recognition (cell fingerprint); important in transplantation
Plasma Membrane is semipermeable and selectively permeable: some molecules may pass through freely (e.g.: water); others must be
assisted across
Types of Membrane
Proteins:
Channel Proteins: create
transient hydrophilic
channel for small molecules & ions to flow into & out of cell
Carrier Proteins: selectively interact with small molecules or ions to assist them
across the membrane
Cell Recognition
Protein: Cell Identity; individual-specific groups of proteins on extracellular side of membrane (e.g.: MHC/HLA
(Human Leukocyte Antigen) – important to match with donor to avoid
rejection of transplanted organ or tissue)
Receptor Protein:
Interacts with specific molecule to transmit some type of signal or
communication (electrical, chemical or contact) between cells (e.g.: hormone receptors)
Enzymatic Protein:
Catalyzes (speeds up) some specific reaction which results in a cellular
response
Cell Adhesion Molecules
(CAMs): guide interactions between
cells
Cytosol: consists of cytoplasm (the fluid within the cell outside the nucleus) &
organelles
Endoplasmic Reticulum:
(ER)
-
Rough ER:
associated with ribosomes; proteins translated on ribosomes associated
with the rough ER will be transported and/or secreted outside cell
- begins processing &
modification of these proteins
-
Smooth ER:
synthesizes phospholipids in all cells; various other cell type-specific
functions
- synthesizes steroid hormones in
testes, and detoxifies drugs in liver cells
Ribosomes: site
of protein synthesis in the cell
-
free in cytoplasm
(polyribosomes) or associated with rough endoplasmic reticulum
-
2 subunits (large &
small); mRNA is threaded through subunits during translation (protein
synthesis)
Golgi apparatus: completes modification of proteins from rough ER (proteins transported
to Golgi in vesicles)
-
modification of proteins & lipids (addition of carbohydrate
chains (glycosylation))
-
also transports organic
molecules in vesicles; some become lysosomes
Mitochondria: produces
energy
-
site of cellular
respiration (ATP production from
carbohydrates)
-
also have folded
membrane system (folds are cristae,
inner fluid-filled space is the matrix)
-
extensive membrane
systems are important in both chloroplasts and mitochondria for ATP production
Lysosomes:
vesicles with digestive enzymes to break down macromolecules & cell
debris
-
loss of some or all
lysosome function in inherited disorders (Tay-Sachs disease) may lead to
accumulation of unwanted molecules (& related toxicity)
Peroxisomes are vesicles that contain enzymes for oxidizing certain organic molecules with the release of hydrogen
peroxide (toxic, but breaks down into water & oxygen)
Cytoskeleton: composed of microfilaments, microtubules, &
intermediate filaments
-
functions in maintaining
shape of cell and movement of subcellular structures
-
microfilaments: thinnest elements of cytoskeleton; help generate
movement & provide mechanical support
-
actin filaments combine with myosin in muscle cells to enable muscle
movement
-
microtubules:
composed of tubulin dimers
coiled into tubelike structures
-
concentrated &
arranged as rings of nine doublets or triplets in centrioles, cilia, and
flagella
-
microtubules involved in
movement
Centrosome: located near nucleus; consists of centrioles &
pericentriolar material
-
centrioles: cylindrical structures composed of 9 clusters of
three microtubules (triplets) arranged in circular pattern
-
pericentriolar
material consists of hundreds of
tubulin complexes
-
involved in organization
of spindle fibers for chromosome movement during mitosis
Cilia and Flagella: composed of microtubules (9 + 2 pattern); used in
movement
-
Cilia present in some unicellular protists (Paramecium)
and cells of respiratory tract in animals
-
Flagella present in some unicellular protists (Euglena)
and sperm cells
Vesicles (vacuoles): membrane-bounded organelles for transport or storage
-
formed by cell membrane,
ER or Golgi apparatus
Nucleus: stores genetic information in all eukaryotic cells
-
DNA is organized into distinct chromosomes
-
Chromosomes are packaged with proteins to form chromatin
-
dark regions within the
nucleus are nucleoli (1 or more
per cell)
-
within each nucleolus, ribosomal RNA is produced and joins with ribosomal
proteins to form ribosomes
-
the nucleus is bounded
by a porous membrane, the nuclear envelope, which regulates passage of molecules into & out of the nucleus
Plasma membrane
transport:
Diffusion: movement of molecules from a region of higher
concentration to a region of lower concentration (down concentration gradient)
-
evenly distributes
molecules in water (equilibrium)
-
lipid soluble molecules,
gases (oxygen, carbon dioxide) and water can diffuse across the plasma membrane
Facilitated
Diffusion: passage of small molecules (glucose, amino acids)
across the plasma membrane even though they may not be lipid-soluble
-
a carrier protein assists
movement of molecules down concentration gradient
-
no energy
is required
Osmosis:
diffusion of water across a differentially permeable membrane (plasma
membrane)
- important in water retention
Tonicity: the strength (solute concentration) of a solution in
relation to osmosis
-
in cells, the solute concentration of a solution with respect
to that solute concentration inside the cell
-
isotonic (isoosmotic)
solution: the net solute
concentration of the solution equals that inside the cell
-
hypotonic
(hypoosmotic) solution: the net
solute concentration of the solution is less that inside the cell; animal cells
swell (& eventually will burst – hemolysis)
-
hypertonic
(hyperosmotic) solution: the net
solute concentration of the solution is greater that inside the cell; animal
cells shrink – crenation
Filtration: a pressure gradient pushes solute-containing fluid
(filtrate) from area of high pressure to area of low pressure
-
forces water &
solutes through membrane or capillary wall by hydrostatic pressure
Active Processes:
Active Transport: movement
of small molecules or ions across membrane assisted by carrier protein and against
concentration gradient –
from region of lower concentration to region of higher concentration
-
requires energy
(ATP)
-
(e.g.: sodium-potassium pump)
-
secondary active
transport: uses energy derived
from primary active transport to drive other substances across membrane
Vesicular
(membrane-assisted) transport:
-
transport of macromolecules into or out of cell in vesicles
-
vesicle: small, spherical sac that has budded off existing
membrane
-
requires energy
-
Exocytosis: moves
macromolecules out of cell through vesicles budding off plasma membrane
-
Endocytosis: moves macromolecules into cell through vesicles budding off plasma membrane
-
Phagocytosis: endocytosis of large food particles or invading cells (bacteria)
- Common in macrophages of the immune system
-
Pinocytosis
(bulk-phase endocytosis): endocytosis of a liquid or very small particles (sampling of
extracellular environment)
- Receptor-mediated
endocytosis: endocytosis involving a receptor protein and its ligand (molecule it binds)
-
receptor proteins
cluster together in clathrin-coated pits
Cell Cycle: consists of Interphase and Mitosis
-
the time required for
cell division is relatively constant for a given cell type of a given organism
(usually between 14 and 24 hours)
Interphase:
consists of G1, S, and G2 stages.
-
DNA is replicated &
cell synthesizes proteins for mitosis & cell division
Cell Division:
-
cell division involves
nuclear division and cytokinesis (division of cytoplasm)
-
normally, most
eukaryotic cells have two
copies of each chromosome (2n, or diploid state); the 2 chromosomes of each
pair are called homologous chromosomes or homologs
-
the reproductive cells
(or gametes) have only one copy of each chromosome (n or haploid state)
-
human somatic cells have
23 pairs of chromosomes; gametes have 23 chromosomes
Mitosis: M stage
-
Prophase:
chromatin condenses and the nuclear membrane begins disintegration.
·
spindle fibers form to move chromosomes in cell
-
Metaphase:
Chromosomes align at metaphase plate attached to spindle fibers
-
Anaphase:
Chromosomes move toward opposite poles of the cell due to disassembly of spindle fibers
-
Telophase:
Chromosomes are at opposite poles of the cell; nuclear envelope reforms
around each set of chromosomes, and spindle disappears. Cytokinesis beginsŠ
Cytokinesis: cells divide by means of a cleavage furrow
Cell Differentiation: specialization of a cell to carry out a specific function
-
stem cells: cells that retain the ability to divide without
specialization
·
division of stem cells
yields 2 stem cells or a stem cell & a progenitor cell
·
allow for growth &
repair of tissues
-
progenitor cells: divide to produce mature cells within a tissue
·
can generally form a few
different cell types
-
many organs (if not all)
in an adult retain a few stem cells or progenitor cells for growth & repair
-
stem cells in bone
marrow can produce red blood cells, white blood cells & platelets
-
specialization involves
expression of different genes in different stem cells to produce different
proteins (e.g.: muscle progenitor cells produce contractile proteins)
Cell Death
-
apoptosis: programmed cell death
·
DNA in chromosomes is
chopped up and cell is fragmented into many vesicles; a scavenger cell then
removes the remains
-
apoptosis is a normal
part of development, rather than a result of injury or disease
-
in fetus, apoptosis
removes immune cells that are not useful (e.g.: immune cells that may attack
our own tissues) and extra brain cells
-
in adult, apoptosis may
remove skin cells that have been burned (e.g.: sunburn)
Chapter 4: Cellular Metabolism
- metabolism: all chemical reactions occurring in cells & necessary to maintain life
o anabolism: reactions that build up molecules (larger molecules are built from smaller molecules); generally requires energy
§ dehydration synthesis is used to join 2 molecules
§ dehydration
synthesis: a bond is
formed between 2 molecules with
removal of water
§ when
2 monosaccharides are joined to form a disaccharide, an –OH is removed
from 1 monosacchraide and an –H is removed from the other; the –OH
and –H join to form water (H2O)
§ fatty
acids are joined to glycerol by dehydration synthesis
§ amino acids are joined to form a dipeptide by dehydration synthesis (a peptide bond is formed)
o catabolism: reactions that break down molecules (larger molecules are broken down into smaller molecules); often releases energy
§ hydrolysis is used to break apart 2 molecules
§ hydrolysis: a bond is broken between 2 molecules by addition of water
§ hydrolysis
is the opposite of dehydration synthesis
§ when
a disaccharide is hydrolyzed to form 2 monosaccharides, water is split and an
–OH is added to 1 monosacchraide and an –H is added to the other
Control of Metabolic Reactions
Enzymes: increase the rate of a chemical reaction by lowering
its activation energy
-
enzymes are almost
always composed of proteins
-
enzymes are organic catalysts
(catalysts speed up chemical
reactions)
-
enzyme reacts with a specific substrate to form a specific product; the part of an enzyme molecule where the substrate
binds is called the active site
-
enzymes bind to
substrates based on shape (lock & key mechanism)
-
example: the enzyme catalase binds to hydrogen peroxide (the substrate) at its active site & speeds its
conversion into water & oxygen
(the products)
-
often assist each step
of a metabolic pathway
-
enzymes are not changed by chemical reaction (usually)
-
enzyme activity
increases with increased concentration of enzyme or substrate
-
enzymes (like other
proteins) can be denatured by heat, chemicals, altered pH...
-
many enzymes require a
nonprotein cofactor; an
organic cofactor is called a coenzyme
Energy for Metabolic Reactions
Energy: the capacity
to do work (change or move matter)
-
energy forms: heat, light, sound, electrical energy,
mechanical energy, chemical energy
-
most metabolic reactions use chemical energy (ATP)
-
chemical energy is released when chemical bonds are broken
-
heat (burning molecules) breaks chemical bonds to release energy
-
oxidation: addition of
oxygen (or removal of hydrogen/electrons)
-
glucose oxidation in cellular respiration releases energy for cellular reactions
-
enzymes reduce the large amounts of energy required for
oxidation during cellular respiration
Cellular Respiration: the complete breakdown of glucose to carbon dioxide and water
- includes glycolysis, the citric acid cycle & the electron transport chain
-
electrons captured move through the electron transport chain
to provide energy to produce ATP (adenosine triphosphate)
- glucose metabolism is an oxidation-reduction reaction. Glucose is oxidized and oxygen is reduced
ATP (Adenosine
Triphosphate)
-
ATP is a nucleotide that provides energy for most of the chemical
reactions occurring within cells
-
energy is released when the terminal phosphate is hydrolyzed (cleaved by addition of water)
-
the overall reaction
is: ATP Þ
ADP + P
+ Energy (7.4 kcal/mole ATP)
-
energy released from
this reaction is used to drive forward energy absorbing reactions in cells
Glycolysis: the breakdown of glucose (6C) to 2 pyruvate (3C) molecules
- net gain of 2 ATP molecules (4 produced, 2 used)
- no oxygen is required – anaerobic phase of cellular respiration
Aerobic respiration: included citric acid cycle & electron transport chain
- 38 molecules of ATP can be produced from 1 glucose molecule (2 from glycolysis)
- oxidative phosphorylation: uses oxidation to add phosphates to ADP to form ATP
- releases heat & form carbon dioxide & water
- oxygen is final electron acceptor – combines with hydrogens & electrons to form water
Genetic information
-
gene: sequence of DNA used to form a polypeptide (contains
the code for a ploypeptide)
-
genome: all the DNA within the nucleus of a cell
DNA Synthesis
DNA replication is carried out by the enzyme DNA Polymerase, as well as some additional protein factors
-
DNA helicase unwinds the double helix in preparation for
replication
-
DNA Polymerase has a
proofreading activity to correct replication errors (adding the wrong
base). The corrected error rate
(after proofreading) is 1 in 1 billion bases
-
DNA replication is semiconservative: each newly replicated DNA molecule consists of 1 old
strand from the original double- stranded DNA molecule, and 1 newly synthesized
strand
Gene
Expression:
Transcription: DNA is transcribed to RNA in the nucleus
-
3 types of RNA can be
made:
-
mRNA (messenger RNA): directs the synthesis of a protein
-
rRNA (ribosomal RNA): rRNA along with proteins comprise the structure of the 2
subunits of the ribosome
-
tRNA (transfer RNA): binds to an amino acid & delivers
it to the ribosome during protein synthesis; has anticodon that binds to mRNA
codon
-
transcription is carried
out by a 5¹ to 3¹ RNA Polymerase, as well as additional protein factors
Translation:
mature mRNA is translated to protein in the cytoplasm
-
translation occurs at
the ribosomes
-
many ribosomes may
synthesize protein from the same mRNA molecule at the same time (polyribosomes)
-
tRNA molecules carry amino acids to the ribosome during
translation (a tRNA for each amino acid)
-
ribosome subunits
associate immediately prior to translation, and dissociate following
translation
-
codon: sequence of 3 nucleotides in mRNA that specify 1
amino acid in a polypeptide
-
3:1 ratio for # nucleotides in mRNA : # amino acids
in polypeptide
-
ribosomes bind mRNA and
begin translation, usually, at the first AUG (start) codon
-
one of 3 stop codons (UAA, UAG, UGA) signals the ribosome to stop
translation of the mRNAŠ following translation, a release factor cleaves the
complete polypeptide from the last tRNA and the ribosome, and the polypeptide
leaves the ribosome
Chapter 5: Tissues
Epithelial Tissue (epithelium): a sheet of cells that lines a body cavity or covers a body surface
- covering & lining epithelium: skin & lining of body cavities
- glandular epithelium: forms glands
-
many functions:
protection, absorption, secretion, excretion, filtration, sensory reception
-
capable of regeneration
-
epithelial tissue is avascular
- basement membrane: anchors epithelium to underlying connective tissue; part of extracellular matrix
Classification of Epithelia:
- squamous (flattened), cuboidal (cube-shaped), & columnar (column-shaped) cells
- simple (1 layer) or stratified (multiple layers)
Simple Squamous Epithelial Tissue: single layer of flattened cells with disc-shaped nuclei & little cytoplasm
- locations: in kidney glomeruli, air sacs of lungs, heart lining, blood vessels & lymphatic vessels, lining of ventral body cavity
- functions: diffusion & filtration; secretes lubricating substances in serosae
Simple Cuboidal Epithelial Tissue: single layer of cube-shaped cells with large spherical nuclei; often seen in circular pattern when cut in cross section
- locations: in kidney tubules, ducts of small glands, ovary surface
- functions: secretion & absorption
Simple Columnar Epithelial Tissue: single layer of column-shaped cells with oval nuclei; some have cilia or microvilli; may include goblet cells
- locations: nonciliated in most of digestive tract, gallbladder & excretory ducts of some glands; ciliated in small bronchi, some regions of uterus
- functions: absorption, secretion of mucus, enzymes...; ciliated propels mucus, reproductive cells
Pseudostratified Columnar Epithelial Tissue: single layer of mostly column-shaped cells with different heights (some don't reach apical surface) & nuclei at different levels; some have cilia; may include goblet cells
- locations: nonciliated in male sperm-carrying ducts & ducts of large glands; ciliated type lines trachea & most of upper respiratory tract
- functions: secretion & propulsion of mucus
Stratified Squamous Epithelial Tissue: multiple layers; basal layer cuboidal or columnar - carry out metabolism & mitosis; outer layers are keratinized
- locations: nonkeratinized in most of digestive tract, gallbladder & excretory ducts of some glands; keratinized in epidermis of skin
- functions: protects underlying tissues
Stratified Cuboidal Epithelial Tissue: several layers – lines lumen of ducts/tubes
- locations: ovarian follicles, seminiferous tubules & some large ducts of glands (mammary, sweat, salivary, pancreatic)
-
functions: protection, secretion
Stratified Columnar Epithelial Tissue: several layers - basal layer usually cuboidal
- locations: male urethra & vas deferens; parts of pharynx
- functions: protection, secretion
Transitional Epithelial Tissue: several layers - basal layer cuboidal or columnar; surface cells dome-shaped or squamous-like (depending on stretch)
- locations: ureters, bladder & part of urethra
-
functions: stretches & distends urinary organ
Glandular Epithelial Tissue
Gland: 1 or more cells that produce & secrete a specific product
- unicellular or multicellular
Endocrine glands: release product into extracellular space
- ductless glands... eventually lose their ducts
Exocrine glands: release product to an epithelial surface
-
includes mucus, sweat,
oil, & salivary glands
-
merocrine glands: secrete product by exocytosis
·
serous cells: secrete watery fluid with enzymes called serous fluid
·
mucous cells: secrete mucus, containing the glycoprotein mucin
§
goblet cells: serve protective function in gastrointestinal &
respiratory tracts
-
apocrine glands: lose small portions of gland during secretion
- holocrine glands: accumulate product until gland ruptures
Connective Tissue: most abundant primary tissue
-
connective tissues bind
structures, provide support & protection, serve as frameworks, fill spaces,
store fat, produce blood cells, protect against infections & help repair
tissue damage
- cells in connective tissue are varied and usually divide
- range of vascularity, but most have good blood supplies
- extracellular matrix (collagen or elastin fibers; calcium phosphate (bone)
- ground substance: fills space between cells & contains fibers
Connective Tissue Cells:
- fibroblasts (many types)
- chondrocytes (cartilage) & osteocytes (bone)
- white blood cells, mast cells, macrophages (blood,...)
Connective Tissue Fibers:
- collagen: thick fibers (of collagen protein); provide tensile strength (resist tension)
- elastic: thin fibers made of elastin protein; stretch easily
- reticular: very thin collagenous fibers; lend delicate support (lymphoid tissues)
Connective Tissue Types:
Areolar (Loose) Connective Tissue: gel-like matrix with all 3 fiber types; fibroblasts, mast cells, macrophages & some white blood cells
- location: under many epithelia (forms lamina propria); around organs & capillaries
- functions: cushions organs; many immune cells regulate immunity
Adipose Connective Tissue: closely packed adipocytes (fat cells with large fat droplet)
- location: under skin, around kidneys & eyeballs, within abdomen, breasts
- functions: cushions organs; reserve food fuel, insulation
Dense Connective Tissue: dense (primarily) parallel collagen fibers, few elastin fibers; fibroblasts
- location: tendons, ligaments, dermis of skin, digestive submucosa, fibrous capsules of organs & joints
- functions: attaches muscles to bone & other muscles, attaches bones to bones; withstands high stress; adds structural strength
Cartilage: mostly water; no blood vessels or nerves
- surrounded by a layer of dense irregular connective tissue - the perichondrium, which contains blood vessels
- contains chondrocytes in lacunae, ground substance & fibers
-
3 types: hyaline, elastic & fibrocartilage
- hyaline cartilage: amorphous firm matrix; collagen fibers form glassy (invisible) network; chondrocytes in lacunae
· location: embryonic skeleton, covers long bones in joints, costal cartilage of ribs, cartilage of nose, trachea & larynx
· functions: support, cushioning, resists stress
-
elastic cartilage: similar to hyaline cartilage, with elastin fibers in
matrix
· location: external ear (pinna), epiglottis
· functions: maintains shape while adding flexibility
-
fibrocartilage: similar to hyaline, less firm with thick collagen
fibers in matrix
· location: intervertebral discs, pubic symphysis, knee joint discs
· functions: tensile strength, absorbs shock
Bone: hard calcified matrix, many collagen fibers, well-vascularized, osteocytes in lacunae
- location: bones
- functions: support, levers for muscles, calcium storage, blood cell formation (hematopoiesis) in marrow
Blood: red blood cells (erythrocytes), white blood cells (leukocytes) & platelets in fluid matrix (plasma)
- location: in blood vessels
- functions: transports oxygen & carbon dioxide, nutrients, wastes & other substances
Muscle Tissue:
Skeletal Muscle: multinucleate, long cylindrical cells with peripheral nuclei; striated; voluntary muscle
- location: attached to bones of skeleton
- function: contraction helps move bones
Smooth Muscle: uninucleate, spindle-shaped cells; centrally located nucleus; nonstriated; involuntary muscle
- location: lines hollow passageways such as: walls of blood vessels, airways to lungs, stomach, intestines & bladder
- function: contraction helps constrict or narrow lumen of blood vessels, break down & move food through GI tract, move fluids & eliminate wastes
Cardiac Muscle: one centrally located nucleus (usually); striated; branched; intercalated discs (desmosomes & gap junctions) between cells
- location: myocardium of heart
- function: contraction helps propel blood from heart to tissues
Nervous Tissue: neurons & neuroglial cells (supporting cells)
- location: brain, spinal cord & nerves
- functions: transmit electrical signals from sensory receptors to effectors
Types of Membranes:
-
serous: fluid membrane surrounding organs... pleura (lungs),
pericardium (heart), peritoneum (digestive organs)
o visceral & parietal
- mucous: lines body cavities (digestive tract, respiratory tract)
o specialized cells (glands) may secrete mucus
-
cutaneous
(epithelial): skin
-
synovial membranes: line cavities of freely movable joints
o areolar
CT with elastic fibers & adipocytes