Unit 2a: Cells and Tissues Flashcards
List and describe the general functions of the Cell membrane
i. Acts as a physical barrier separating the ECF from the
ICF.
ii. Regulates exchange of molecules between the ECF
and ICF.
- Semipermeable (or selectively permeable)
membrane controls what molecules (solutes) can
move into or out of the cell.
iii. Communication between cell and environment
–receptors on outer surface of membrane detect and
respond to signals (chemical and physical) in the
environment (e.g. levels of regulated variables – like
temperature, ion concentration, CO2, etc.; some
hormones, neurotransmitters, etc).
iv. Structural support for the cell
– cytoskeleton attaches
to membrane proteins and gives cell shape. Some
have protein junctions that help connect the
membranes of adjacent cells
What is the cell membrane composed of?
Composed mostly of lipids and
proteins
Ratio of lipids & proteins
varies with more metabolically
active structures/cells having more
protein in their membranes
Describe why the membrane is called a Fluid Mosaic Model
proteins appear
floating around in a sea of lipids
(like boats in a harbour). Fluid
because the proteins/lipids can
move two dimensionally within the
membrane (i.e. they are not fixed
in space)
List the parts of a cell membrane
- phospholipid bilayer
- cholesterol
3.sphingolipids - membrane proteins
describe the role of the phospholipid bilayer
- Creates hydrophobic barrier between ECF and ICF
- Phosphate heads (polar & hydrophilic) orient
towards ECF or ICF; fatty acid tails (non-polar &
hydrophobic) orient towards each other and form the
hydrophobic barrier - 3 main types of phospholipids in the membrane. They
differ in their R group and the degree of saturation of their
fatty acids, and are asymmetrically distributed between the
outer and inner parts of the bilayer. Asymmetric
distribution provides mechanical stability to the membrane
List the main types of phospholipids
- Phosphatidylethanolamine – inner layer
2) Phosphatidylserine – inner layer, -ve charged head.
3) Phosphatidylcholine – mostly outer laye
: Which phospholipid
is most abundant in the
membrane?
Phosphatidylcholine
describe the role of Cholesterol in a cell membrane
Located between fatty acid chains of adjacent
phospholipids
- Slows diffusion of molecules across membrane; can
block small water soluble molecules. - Determines membrane fluidity
- Prevents membranes from becoming too rigid at cold
temperatures or too fluid at high temperatures by
interfering with movement of fatty acid chains. - Keeps fatty acids together at high temps, (prevents
bilayer from breaking apart) and keeps them apart at
low temps (prevents bilayer from freezing).
Describe the role of Sphingolipids in the membrane
Ø E.g. sphingomyelin
Ø Have longer fatty acid tails than phospholipids.
Ø Form lipid rafts
lipid rafts
aggregation of sphingolipids
with a higher density of cholesterol than other
areas of the membrane.
- Some membrane proteins can only be found in
lipid rafts, for example some G-protein coupled
receptors (common receptor for detecting
peptide or protein neurotransmitters, and
hormones, as well as odours, light, etc.). - Studies have associated lipid rafts with
numerous diseases including Alzheimer’s,
Parkinson’s, and recently COVID-19
List the types of membrane proteins
- integral; lipid anchored and transmembrane
- peripheral
Integral Proteins
Permanently attached to cell membrane
Transmembrane Proteins
- type of integral membrane protein
- Cross the entire membrane.
- Have one (bitopic) or more (polytopic)
membrane spanning regions.
-The protein’s non-polar (hydrophobic)
regions (made up of 20-25 non-polar amino
acids) are embedded in the hydrophobic
regions of the phospholipid bilayer.
- The polar (hydrophilic) regions interact with
either the ECF or ICF
Lipid-Anchored Proteins
Ø Monotopic = permanently attached to one
surface of the membrane (i.e. do not cross
entire membrane)
Ø Many are attached to lipid portion of
phospholipid bilayer by covalent bonds.
Peripheral proteins
Attached to integral proteins or to polar heads of
phospholipids by non-covalent interactions
(weaker bonds and therefore not permanent)
Membrane carbohydrates
Ø Found only on membrane surface
facing the ECF
Ø Attached to lipids (forming glycolipids)
or to proteins (forming glycoproteins
glycocalyx
- formed from membrane carbs
- protective layer around cell
cytoplasm
spans area between the cell membrane and the nucleus
List the components of the cytoplasm of a typical cell
- cytosol
- membranous organelles
- inclusions
- protein fibres
Cytosol
intracellular fluid made of of
H2O, dissolved (soluble) nutrients, proteins,
ions and waste products
Membranous organelles
compartments
in cell separated from the cytosol by a
phospholipid membrane
Inclusion
insoluble material in direct
contact with the cytosol
Protein fibers
involved in structural
support for the cell and/or movement
List the membranous organelles
- mitochondria
- ER
- Golgi apparatus
- lysosomes
- peroxisomes
Mitochondria
double membrane; site of most ATP
synthesis
Endoplasmic reticulum (ER)
- network of membranous tubes connected to nuclear membrane.
Two types: - rough and smooth
Rough ER
covered in ribosomes, so involved in
protein synthesis and in transporting and
modifying proteins assembled by the ribosomes
Smooth ER
– no ribosomes; synthesizes lipids (e.g.
phospholipids for membranes; fatty acids;
steroids; sebum in skin oil gland cells, etc
Golgi apparatus
– stacks of membranous tubes
(cisternae) that modifies proteins and packages them
into vesicles for delivery to different areas (e.g. to the
cell membrane, to the outside of the cell, to other
membranous organelles, etc)
Peroxisomes
contain enzymes that breakdown fatty
acids and amino acids
Lysosomes
contain digestive enzymes that breakdown
worn out cell parts and can be used by some cells to
destroy viruses and bacteria
- Can also trigger apoptosis
(programmed cell death) if the cell is damaged - like the digestive system of the cell
Nucleus
Control center of cell
- nuclear envelope
- nucleolus
- Contains chromatin (DNA + histone proteins)
Nuclear envelope
double membrane with nuclear
pores (allow molecules to be passed back and forth
between cytosol/rough ER and inside of nucleus (e.g.
messenger RNA)
Nucleolus
dense region of DNA and RNA in nucleus
responsible for synthesis of ribosomal RNA units that
become the ribosome
List the inclusions
ribosomes
glycogen granules
lipid droplets
pigment proteins
Ribosomes
protein subunits that synthesize
proteins (translation).
Can be:
fixed or free (can alternate between the 2)
Fixed ribosomes
e.g. attached to ER (proteins made here
will go to the Golgi apparatus and be packed
into vesicles that will deliver them to the ECF,
to the cell membrane or to lysosomes)
Free ribsomes
– suspended in cytosol (proteins made
here destined for cytosol or mitochondria, or
persoxisomes
Glycogen granules
storage form of glucose in
liver cells and muscle cells
Lipid droplets
– storage of triglycerides in fat
(adipose) cells and liver cells.
Pigment proteins
– e.g. hemoglobin in red blood
cells; melanin in skin and hair cells
List the different types of protein fibres
a. cytoskeleton
- microfilaments
-IF
-microtubules
b. cilia and flagella
c. centrosomes and centrioles
describe the composition and function of microfilaments
mall diameter (7 nm) protein
fibers made of the protein actin
Functions:
structural; movement (acts with motor proteins,
to produce movement e.g. movement of white
blood cells through tissues; cytokinesis during
cell division; contraction of skeletal muscles)
describe the composition and function of intermediate filaments
intermediate diameter
filaments (8-10 nm) made of different proteins
depending on tissue type, e.g. in skin, hair and
nails the protein is keratin
Microtubules
large diameter fibres (~25 nm)
made of protein tubulin
- Act as a track for
some motor proteins to move structures
around the cell - Also important to cell division
(moves chromosomes and pulls them apart)
Describe the functions of the cytoskeleton:
i. Give cell shape (like scaffolding.).
ii. Internal organization of cells – stabilizes position of
organelles.
iii. Intracellular transport – facilitates transport into
the cell and within the cell (acts as a track for
motor proteins that can move organelles).
iv. Assembly of cells into tissues – interaction of
cytoskeleton with membrane proteins and
secreted proteins found on the extracellular
surface of cells helps provide physical strength.
v. Movement – of the cell itself or parts of the cell
(cilia/flagella have microtubules in their structure
Centrosome & Centrioles
assembles tubulin into
microtubules that direct DNA movement during cell
division (mitosis & meiosis).
*MTOC
Cilia and Flagella
Ø Both have microtubules in their structure.
Ø Cilia project into the ECF and wave back and forth to
move fluid across the surface of cells.
Ø In humans, only sperm cells have flagella, which propel
sperm through fluid
motor proteins
convert stored energy into direct movement
list the 3 types of motor proteins
- myosins
- kinesins
- dyneins
- all use ATP to propel themselves
myosins
bind to actin
involved in muscle contractions
kinesins and dyneins
assist in movement of vesicles along MTs
describe the 3 parts of a motor protein
2 heads that bind to cytoskeletal fibre
a neck and tail that binds organelles
Describe protein synthesis
- RNA for protein synthesis is made from DNA templates in the nucleus
- then transported to the cytoplasm through the nuclear pores
- Inthe cytoplasm, proteins are synthesized on ribosomes that may be
- free inclusions
- or attached to the rough endoplasmic reticulum
- The newly made protein is compartmentalized in the lumen of the rough ER 5
- where it is modified before being packaged into a vesicle
- The vesicles fuse with the Golgi apparatus, allowing additional modification of the protein in the Golgi lumen.
- The modified proteins leave the Golgi packaged in either storage vesicles
or secretory vesicles whose contents will be released into the extracellular fluid 10.
List all the different compartments involved in protein synthesis
nucleus
cytoplasm
ribosomes
er
golgi apparatus
vesicles
What are the 3 major types of cell junctions?
- communicating junctions (gap junctions)
- occluding junctions (tight junctions)
- anchoring junctions (desmosomes)
Communicating junctions (e.g. Gap junctions
protein clusters called connexins form pores between
adjacent cells
Allow molecules to pass directly from
one cell to another
Common in cardiac and smooth
muscle so that multiple cells can contract as a uni
Occluding junctions (e.g. Tight junctions)
regions of
membranes from two adjacent cells fuse together
preventing material from passing in between the two
cells
Common in intestinal cells (enterocytes) lining
the gut – blocks potentially harmful substances from
moving between cells and crossing into the blood.
Anchoring junctions (e.g. desmososmes)
connects
cells to each other and to extracellular proteins (acts
like a staple or a rivet holding cells together)
List the 4 major types of tissue
- epithelial
- connective
- nervous
- muscle
Describe the basic structure of an epithelium
- Structure: one or more cells stacked on a
basement membrane (basal lamina) with a free
surface (the apical surface) that faces a
cavity/lumen - named according to how many layers of cells and cell shape
List some characteristics of epithelial tissue
- Avascular (no blood supply)
- Closely packed cells
- line the cavities and surfaces of the body
Ø E.g. lining of the digestive tract; lining of the
thoracic cavity; lining of the bladder, lining of the
chambers of the heart and blood vessels (called
endothelium). - Makes up secretory portions of exocrine and
endocrine glands (e.g. much of the pancreas,
sweat glands, salivary glands, etc). - any substance that enters or leaves the internal envir. of the body must cross an epithelium
What are the 5 function categories of epithelial tissue?
- exchange
- transport
3.secretory - protective
- ciliated
Exchange Epithelia
Ø Cell shape: Thin flattened (squished cells)
Ø Allow gas exchange
Ø Line the blood vessels and lungs
Ø Classified as simple squamous epithelia – simple
because there is one layer of cells, squamous
meaning “flat”)
Transporting Epithelia
Ø Cell shape: cuboidal or columnar (cubes or
rectangles)
Ø Apical membrane faces lumen/cavity
Ø Selectively move substances between the ECF
and ICF
Ø Simple epithelia such as those found lining the
stomach/intestines/kidney tubules.)
Ciliated epithelia
Ø Cell shape: square (cuboidal) or rectangular
(columnar)
Ø Cilia on surface beat back and forth and move fluids
across the outer surface of the cells.
Ø Found in nose, in trachea, uterine tubes, etc
Protective Epithelia
Ø Stratified epithelium – many layers of cells to protect
against abrasion. Cells close to surface are flat
(squamous) but are cuboidal close to the basement
membrane.
Ø Blocks movement of molecules between ECF and ICF
Ø Includes epidermis of skin, lining of the mouth, parts
of the pharynx, esophagus, urethra, vagina, etc.
Secretory epithelia
Ø Cell shape: varies depending on gland, but typically cuboidal or columnar.
Ø Produce and secrete a substance into the extracellular space
Ø Two types
- exocrine and endocrine glands
Exocrine glands
Ø Secretions often travel through ducts to the reach the external
environment
Ø E.g. sweat glands, salivary glands, digestive enzymes from
pancreas; goblet cells that secrete mucou
Endocrine glands
Secrete hormones into the ECF (first into ISF, then into blood plasma).
Ø No ducts required
Ø E.g. thyroid gland, Islets of Langerhans in pancreas
Extracellular matrix
extracellular material that is synthesized and secreted by the cells of a tissue
2 components:
proteoglycans and insoluble protein fibres
List some of the major characteristics of connective tissue
Ø Cells separated by a non-living extracellular matrix
(ECM). Exact composition of ECM determines the
type of connective tissue and its properties
Ø Cells can be fixed in place (as in bone), or can be
mobile (as in blood)
Ø 3 cell types:
a. -blasts (build ECM);
b. -cytes (maintain ECM);
c. -clasts (break down ECM)
Ø E.g. in bone – osteoblasts, osteocytes, osteoclasts
List some of the major characteristics of connective tissue
Ø Cells separated by a non-living extracellular matrix
(ECM). Exact composition of ECM determines the
type of connective tissue and its properties
Ø Cells can be fixed in place (as in bone), or can be
mobile (as in blood)
Ø 3 cell types:
a. -blasts (build ECM);
b. -cytes (maintain ECM);
c. -clasts (break down ECM)
Ø E.g. in bone – osteoblasts, osteocytes, osteoclasts
List the components of ECM
Protein fibers
ground substance
Protein fibres of ECM
i. Collagen – gives tissues strength and flexibility
ii. Elastin – gives tissues stretch and recoil
iii. Fibronectin – connects cells to matrix
Ground substance
Ø Mixture of proteoglycans and water and other
soluble or insoluble molecules
Ø Highly variable – can be mineralized with
hydroxyapatite as in bone, or can be a watery
fluid as in blood plasma
List the different types of Connective tissue
Loose CT; areolar CT
Desne CT; irregular or regular
blood
bone
cartilage
adipose
Loose CT (areolar CT)
lots of ground
substance with collagen and elastin
- cells are
fibroblasts
Ø Often the glue holding 2 tissues types together.
For example the epidermis of skin is attached to
the layers below by areolar CT
Dense regular CT
ECM with lots of collagen
fibers all oriented parallel to one another.
Provides tensile strength as in tendons and
ligaments
Dense irregular CT
ECM with lots of collagen
that randomly arranged
Adipose CT
very little ground substance;
no fibers;
cells are adipocytes that contain a
large storage area for triglycerides (cell is
mostly a droplet of fat with cell organelles
pushed out towards the cell membrane
Bone
mineralized ground substance due to
hydroxyapatite (calcium) salts gives bone their
strength;
fiber = collagen;
cells are
osteoblasts, osteocytes and osteoclasts
Cartilage
semi-rigid but flexible ground
substance contains hyaluronic acid;
fibers are
collagen;
cells are chondroblasts,
chondrocytes and chondroclasts.
Found
covering ends of bones at joint surfaces; also
cartilage of ear, nose, larynx (voice-box), etc
Blood
fluid matrix (blood
plasma/intravascular fluid); contains soluble
protein fibers involved in blood clotting
(fibrinogen)
Cells include red blood cells
(RBCs = erythrocytes) and white blood cells
(WBCs = leukocytes)
RBCs transport gases
(O2 and CO2) while WBCs support immune
function
RBCs are located in blood vessels
while WBCs are found in blood vessels and
lymphatic vessels/tissues
Explain what an excitable tissue is
nervous and muscle tissue are excitable (have very little ECM)
- called this bc of their ability to generate and propagate action potentials
Muscle Tissue
Has the ability to generate electrical signals in response
to stimuli that will cause contraction and shortening
List the 3 major types of muscle tissue
- skeletal
- cardiac
- smooth
Skeletal muscle tissue
long multinucleate cells; voluntary contraction
produces force that can move the skeleton and produces
facial expressions.
E.g. your deltoid (shoulder muscle)
contains skeletal muscle tissue. When it contracts, it moves
your humerus (whole arm).
Cardiac muscle tissue
branched uninucleate cells; produces involuntary
rhythmic contractions of heart in order to pump blood
throughout the cardiovascular system
Smooth
involuntary muscle that forms part of the wall of
most internal organs (e.g. stomach, intestines, bladder, uterus,
blood vessels, etc.)
Also forms muscles of the iris of the eye,
which contract to control pupil size and muscles in the skin
(arrector pili muscles that make our hair stand on end)
List the 2 types of neural tissue
Neurons
glilal cells
Neurons
– generate chemical and electrical
signals in response to stimuli that can be
propagated over long distances
Located in
the brain, spinal cord and nerves that go to
all structures in the body.
Glial cells (neuroglia)
– support cells for
neurons that have various functions (we will
look at these more closely when we study
the nervous system)
Explain what an organ is and describe how the skin fits this definition
Organs are made of 2 or more tissue types.
ØSkin contains all 4 of the major tissue types.
Describe what tissue type each layer of the skin is composed of
- Epithelial Tissue is present in :
a. Epidermis = stratified squamous epithelial tissue protects
b. Sweat glands and sebaceous (oil) glands - Connective Tissue is present in:
a. Dermis = dense irregular CT and areolar CT, gives skin strength,
but also flexibility
b. Hypodermis – adipose CT - Muscle Tissue is present in:
a. Arrector pilli muscle – contraction causes hairs in skin to stand
straight up causing “goosebumps” . In other mammals with more
hair, this helps to trap a warm layer of air against the skin in cold
weather. - Nervous Tissue is present in:
a. Sensory receptors for touch, temperature, pain, and pressure,
which are all parts of neurons.
