Chap 3 Flashcards
Cells
Structural units of all living things
Amount of cells in the body
50-100 trillion
Explain the principle of complementarity of cells
Activities of cells are dictated by their shapes and by the types and numbers of subcellular structures they contain
Cells arise from
Other cells. Most body cells from mitosis,
Sex cells come from meiosis
What underlies every disease?
The loss of homeostasis in cells
Examples of the shape of cells
Disc shaped red blood cells, branching nerve cells, cube shaped cells of kidney tubules
Which cells connect body parts, form linings to transport gases?
Epithelial cells,
Fibroblasts,
erythrocytes
Which cells move organs and body parts?
Skeletal and smooth muscle cells
Which cells stores nutrients
Fat cell
Cells that fight disease
Macrophage
Cell that gathers information and controls body function
Nerve cells
Cell of reproduction
Sperm and eggs
Three main parts of a generalized cell
Plasma membrane
Cytoplasm
Nucleus
Plasma membrane
Outer boundary of a cell, acts as selectively permeable barrier
Cytoplasm
Intracellular fluid packed with organelles,
Organelles
Small structures that perform specific functions
Nucleus
Organelle that controls cellular activities
Extracellular materials
Substances contributing to body mass that are outside of the cells
Types of extracellular materials
Extracellular fluid
Cellular secretions
Extracellular matrix
Extracellular fluid includes
Interstitial fluid,
Blood plasma
Cerebrospinal fluid
Interstitial fluid
Body fluid filling the space surrounding cells, lymphatic capillaries and vascular
Function of ECF
Dissolves and transports substances in the body
Has amino acids, sugars, fatty acids, regulatory substances and wastes. Each cell extracts what it needs from the ECF
Cellular secretions
Aid in digestion
(Intestinal and gastric fluids)
Some act as lubricants (saliva, mucus, serous fluids)
Extracellular matrix
Most abundant extracellular material.
Jelly-like has proteins and polysaccharides.
Extracellular matrix function
Helps bind cells, most abundant in connective tissues
Plasma membrane
Phospholipids, cholesterol and proteins.. selectively permeable
What does the plasma membrane separate?
The extracellular fluid from the intracellular fluid
Fluid mosaic model thickness
7-10 nm
Fluid mosaic model
Proteins and cholesterol dispersed in the plasma membrane. Constantly changing.
Lipids in plasma membrane
Phospholipids
Cholesterol
Cholesterol functions in membrane
-Stiffens membrane
-decreases water solubility of membrane
-4 ring structure
Phospholipids functions
-Make basic structure of membrane
-Hydrophobic tails prevent water soluble elements from crossing
Proteins
-Determines which roles the membrane can do
-Transport, communication, receptors, attachment
different shapes have -different functions
Carbohydrates function in plasma membrane
-identify cells so they can sort themselves
-on outer surface of membrane. Like sugar covering a breakfast cereal
Glycocalyx
Covering of carbs on outer surface of cell membrane
Movement of phospholipids
Can move side to side but rarely flip over
Mobility of cholesterol
Can move easily to the other layer
Lipid anchor attaches to
Protein
Integral proteins
Embedded in lipid bilayer
Peripheral proteins
Anchored to membrane or to other proteins but not embedded in membrane
Glycoproteins
Carbs attached to proteins
Glycolypids
Carbs attached to lipids
Types of passive transport across plasma membrane
- Simple diffusion
2.Facilitated diffusion - Osmosis
- Filtration? Happens through capillary walls
Diffusion
Moving from high concentration to low concentration no energy. Try to make dispersion even
Depends on size and charge
Concentration gradient
Moving from high concentration to low concentration
Driving force for diffusion
Kinetic energy of molecules. Constant random high speed motion of molecules and ions. The molecules and ions clash into each other and push each other to help scatter particles
What affects speed of diffusion?
Concentration
Molecular size
Temperature
Explain how Concentration affects diffusion
When there’s a large concentration of molecules in one area, those in the concentrated area are more likely to collide. The collisions push them away
How does molecular size affect the rate of diffusion?
Smaller molecules diffuse more rapidly
Temperature
Higher temperature increases kinetic energy and causes the molecules to interact more rapidly, causing more diffusion to happen
When has a container reached equilibrium?
When the molecules are spread evenly throughout. No net movement molecules move evenly in all directions
Distance molecules travel during diffusion?
1/1000 of a page’s width
Examples of diffusion
Ions across cell membranes
Neurotransmitters between 2 nerve cells
What feature of the plasma membrane lets it be selectively permeable?
The hydrophobic core
Why is the selective permeability of a cell membrane important?
Let’s nutrients go in but keeps bad substances out.
Keeps important proteins in but let’s wastes go out
Facilitated diffusion
Moving with the help of transport proteins down the concentration gradient
Example of facilitated diffusion?
Water passing through aquaporins
Na K moves through or against concentration gradient?
Against
Active transport
Move using energy through membrane
Explain how NaK pump works?
Energy from ATP is used to move 3 Na ions out of cell and 2 K ions into cell.
Primary active transport
Uses ATP directly
Secondary active transport
Move chemicals against gradients using energy but doesn’t use ATP. I stead it uses downhill gradient from ion or molecule . Uses downhill gradient from one ion or molecule to drive uphill movement of another substance
Example of secondary active transport
Na & glucose into cell using cotransport ir symport.
Na ions move down gradient, glucose moves against concentration gradient
Exocytosis
Cells move substances from the intracellular fluid to the extracellular fluid using vesicles
Endocytosis
Membrane pinches in to create a vesicle
Ways to move materials across membranes
Active transport
Passive transport
Exocytosis
Endocytosis
Active process
Cell uses energy to move solutes across membranes
When are active processes used?
Substances too large, insoluble in lipids,
Move against concentration gradient
Types of active membrane transport
Active transport and vesicular transport
Difference between active transport and facilitated diffusion
Active transport Transports specific substances in reverse direction, needs energy
Facilitated diffusion always follows concentration gradients because it uses kinetic energy
Where does the energy in primary active transport come from?
Hydrolysis of ATP which powers pumps (transport proteins)
Secondary active transport energy source
Concentration gradients of ions made by primary active transport pumps. Always move more than one substance and use cotransport protein
Similarities between types of active transport
Primary and secondary active transport both transport specific substances
No transporter no transport
Explain primary active transport
- ATP gets hydrolysed and a Phosphate comes off
- Phosphate binds to the transport protein and gives it energy
- Transport protein changes shape and pumps bound solute across membrane
Examples of primary active transport systems
Calcium and hydrogen pumps
NaK pump
What is the pump protein for the sodium potassium pump?
Na+ -K+ ATPase
Explain the movement that happens thanks to the Na K pump
For every one ATP broken
Three Na+ go out of cell and two K+ go back in
Concentration of K+ in the cell is….
10x higher than outside, reverse is true of Na
Why is the difference in concentration in Na K important?
Let muscle cells and nerve cells function normally.
Let cells maintain fluid volume.
How does the Na K pump almost function continuously?
Na+ and K+ leak slowly but continuously through leakage channels down their concentration gradient, the Na+ -K+ pump operates almost continuously
Electrochemical gradients
Affect the way ions diffuse
Explain secondary active transport
The pump stores energy by moving Na against it’s concentration gradient. Then like water held back by a dam, it can do work as it flows down. A substance moved across a membrane can do work as it leaks back. It drags substances back down
Symport system
2 substances move in same direction
Antiport system
2 substances move in opposite directions.
Example of antiport system
Cotransporter used to regulate pH of cells
Vesicular transport
Fluids containing large particles are transported via membranous sacs
Transcytosis
Moves substances into, across then out of the cell.
Where does transcytosis happen?
Endothelial cells lining blood vessels. Gets substances from blood into interstitial fluid
Vesicular trafficking
Moves substances from one area or organelle to another part of the cell.
What gives energy for vesicular transport?
ATP of Guanosine triphosphate
How do receptors help endocytosis?
Receptors in membrane help determine substances to be transported
Coated pit
Infolding of membrane. How vesicle starts to form. Coated with proteins
Explain the steps of vesicular transport
- Coated pit ingests substance
- Protein coated vesicle detaches
- Coat proteins are recycled to plasma membrane
- Uncoated vesicle fuses with a sorting vesicle called an endosome
- Transport vesicle containing membrane components moves to the plasma membrane for recycling.
- Fused vesicle may fuse with a lysosome to destroy contents or deliver it’s contents to the plasma membrane on the opposite side of the cell
Three types of endocytosis
1.Phagocytosis
2.Pinocytosis
3. Receptor mediated endocytosis
Phagocytosis process
Cell eating
1. Cell engulfs large or solid material
2. Particle binds to surface receptors, pseudopods form around the particle (phagosome)
- Phagosome fuses with lysosome and contents are digested
Phagocytes
WBCs that “eat” substances and destroy harmful materials
Phagocytes move using _____ motion
Amoeboid
Amoeboid motion
Changing shape
Flowing movement of cytoplasm to move across a surface
Pinocytosis explain
“cell drinking”
Membranes folds around ECF with dissolved molecules
Does pinocytosis happen in most cells?
Yes, nonselective way of sampling ECF
In which cells is pinocytosis most important?
In cells that absorb substances like those in the intestines
Explain why the area of the cell membrane remains constant?
Parts of membrane that make vesicles are recycled immediately using exocytosis after use
Receptor mediated endocytosis
Lets specific things go in through endocytosis and transcytosis
- Receptors bind to substances and are taken in then dealt with
Which substances are taken in through receptor mediated endocytosis
Enzymes, insulin, low density lipoproteins and iron
What can hijack receptor mediated endocytosis?
Diphtheria
Flu viruses
Cholera
Phagosome
Membranous sac made by plasma membrane
Exocytosis caused by
Cell surface signals (a hormone binds)
Change in membrane voltage
Uses of exocytosis
Hormone secretion
Neurotransmitter release
Mucus secretion
Ejection of wastes
Secretory vesicle
Membranous sac that is protein coated, moves to cell membrane, fuses the ruptures
Explain the process of exocytosis
- Membrane bound vesicle migrates to plasma membrane
2.proteins at vesicle’s (v and t snares) surface bind
- Vesicle and plasma membrane fuse and a pore opens up
- Vesicle contents are released to the cell’s exterior
Explain docking of exocytosis
V-snares for vesicle recognize t-snares for target. Membranes corkscrew and fuse together, rearrange the lipid monolayers without fusing them
Example of receptor mediated endocytosis
Intake or hormones, cholesterol, iron, most macromolecules
Example of vesicular trafficking
Intracellular trafficking between certain organelles, endoplasmic reticulum, golgi apparatus
Exocytosis examples
Secretion of neurotransmitters, hormones, mucus
Permeability
The ability of molecules and ions to pass through a membrane
Membrane potential
Voltage across a plasma membrane
In which cells is membrane potential most important?
Nerve and muscle cells
Voltage
Electrical potential energy resulting from the separation of oppositely charged particles. In cells oppositely charged particles are ions and what separates them is the plasma membrane
Resting membrane potential + range
Voltage that exists across membrane during resting state of excitable cell
-50 to -90 mV
Why are cells considered electrically polarized?
because even at resting state all cells have a charge that ranges from -50mV to -90mV
The minus sign of a cell’s voltage indicates what?
inside of cell is negative compared to its outside
voltage
charge separation
where does differences of charges only occur?
At the membrane
Describe the charges in the cytoplasm?
Charges in the cytoplasm are electrically neutral . they add up and cancel eachother out. Same with the ECF
permeability
ability of ions and molecules to pass through a membrane
Osmosis
diffusion through selectively permeable membrane by a solvent
Why does the resting membrane potential exist?
diffusion causes ionic imbalances that polarize the membrane. active transport maintains the membrane potential.
which concentration gradient mostly determines membrane potential?
concentration of K+ and the permeability of K+ to the membrane
which anions predominate inside of body cells?
K+ and protein anions
Extracellular fluid contains more of which ion?
Na+ balanced by Cl-
The plasma membrane is somewhat permeable to K + but impearmeable to
protein anions.
why is the cytoplasmic side of the membrane more negative?
k+ can diffuse out following its concentration gradient but the protein anions can’t and so their negative charges stay inside.
Explain the steps of generating the resting membrane potential
K+ diffuses down the steep concentration gradient (out of the cell) via leakage channels, causing a negative charge on the inner face of the plasma membrane.
- K+ also moves back into cell because its attracted to the negative charge on the inner plasma membrane.
- A negative membrane potential (voltage) is created when the amount of K+ going out of cell equals the amount of K+ going into the cell. exiting K+ gradient directly opposes the gradient for K+ entry
Why is membrane potantial largely determined by K+?
At rest, the membrane is much more permeable to K+ than Na+. The active transport of Na and K ions by the Na+ K+ pump maintains the concentration gradients
In many cells, Na+ also contributes to resting membrane potential. Its resting membrane potential usually is -70 mV , but why is K more influential?
K+ diffuses through the membrane much more easier.
Do you need a lot of ions to generate membrane potential?
no. the number of ions is small and does not change the concentrations in any way.
In cells at rest, how many ions cross plasma membrane?
Very few. There is some net movement of K+ out of the cell and Na+ into the cell. Na+ is very strongly pulled in because of the concentration gradient and interior negative charge.
How does active transport help maintain the membrane potential?
rate of active transport must be equal to the rate of diffusion of Na+ diffusion into the cell. If more Na+enters, more is pumped out. The pump maintains the membrane potential and the osmotic gradient. If too much Na+ stayed in the cell and wasn’t removed, the water would go in and the cells would burst.
electrochemical gradient
The diffusion of particles happens because of differences in concentrations and because of electrical charges.
Give an example of how the electrochemical gradient works?
the diffusion of K+ is helped by the concentration gradient but it is opposed by the electrical charges. the electrical charges pull it in but the concentration pushes it out.
The negative charges on the inner part of the cell membrane pull Na in but the impermeability limits Na diffusion
What activates cells to carry out homeostatic functions
respond to extracellular chemicals, hormones, neurotransmitters, some cells interact with others
Extracellular molecules
What percentage of membrane lipid is cholesterol?
20%
Polar region of cholesterol
Hydroxyl group
Non polar region of cholesterol
Fused ring system
Makes up halo the plasma membrane by mass and preforms most functions
Proteins
Types of proteins on cell membrane
1.Transport
2.Receptors
3.Enzymes
4.cell-cell recognition (glycoproteins act as identity tags)
5. Attachment to cytoskeleton and ECM(extracellular matrix)
6. Cell to cell joining
Transmembrane proteins
Go through membrane and peek out on both sides
Types of transmembrane proteins
Channels, pores
Carriers,
Enzymes,
Receptors
Protein pores
Opening of duct or sweat gland
Glycocalyx and cancer
A cancerous cell’s glycocalyx might change almost continuously which lets it avoid the immune system
Tight junctions
Impermeable
Form seals around cell
Prevent molecules from passing between cells
Desmosomes
- Anchoring junctions
2.bind adjacent cells like Velcro
3.helps keep cells from tearing apart
Gap junctions
- Communicating junctions
2.lets ions and small molecules pass from cell to cell
3.important for heart and embryonic cells
Give an example where tight junctions are used
The epithelial cells in the digestive tract are joined by tight junctions. Prevent digestive enzymes and microorganisms from going into bloodstream. Some ions can sometimes pass through
“binding bodies”
Desmosomes
Plaque
Buttonlike thickening on inner surface of plasma membrane
Most important molecules cells use to interact with their environment
Cell adhesion molecules
Plasma membrane receptors
CAMS
1.Cell adhesion molecules
2. Almost on every cell in body
Function of CAMs
Embryonic development and wound repair
(Important where cell mobility is important)
Sticky glycoproteins
Cadherins integrins
Types of CAMs
Explain how CAMs work
1.Molecular Velcro that cells use to anchor themselves to other molecules in extra cellular space
2. Act as arms that help cells move against one another
3. Rally wbcs to infected or injured area
4. Transmit info about changes in extracellular matrix to cell. Bring a variety of responses like cell migration, proliferation, specialization
Membrane receptors
Large and diverse group of integral proteins that serve as binding sites . Some do contact signaling, others chemical signaling, glycoproteins
Contact signaling
Cells recognize each other. Important for immunity and development. Can be used by bacteria and others to identify target tissues
Chemical signaling
Usually comes from outside of the cell
Happens when a ligand binds to a receptor and starts a response
Ligands
Signaling chemicals that bind to membrane receptors
Types of ligands
neurotransmitters, paracrines, hormones
Paracrines
Chemicals that act locally and are rapidly destroyed
How do different cells respond to the same ligand?
Differently. Acetylcholine stimulates skeletal muscle to contract but inhibits heart muscle.
Why do target cells respond differently to the same ligand?
The reaction depends on the cell’s internal machinery.
Explain how ligands work?
When a ligand binds to a receptor, the structure of the cell changes and proteins are altered in some way. For example the membrane proteins can become enzymes or they can open and close channels
G protein coupled receptors
Exert effect through a G protein
G protein
Relays signals between first (hormones or neurotransmitters)and second messengers (cAMP)
Helps activate or inactive a membrane-bound enzyme or ion channel
The activation of G proteins leads to
Second messengers. Intracellular chemical signals that mediate cellular response
cAMP and ionic calcium both activate
Protein kinase enzymes. Transfer phosphate groups from ATP to other proteins, activating a series of enzymes that cause the desired cellular activity
Explain how G proteins work
- Ligand binds to receptor. Receptor changes shape and activates
- Activated receptor binds to G protein and activates it. Causes the release of GDP and bind GTP
- Activated G protein activates or inactives an effector protein by causing a shape change
- Activated effector enzymes catalyze reactions that produce second messengers in the cell
- Second messengers activate other enzymes or ion channels
- Kinase enzymes activate other enzymes. Transfer P from ATP to specific proteins. Activate a series of enzymes that trigger metabolic and structural changes in the cell
Cytoplasm
Cellular material between plasma membrane and nucleus. Site of most cellular activities.
Part of cytoplasm
Cytosol
Organelles
Inclusions
Cytosol
Viscous,
Semitransparent fluid in which the other cytoplasmic elements are suspended.
Properties of both a colloid and a true solution
Which things are dissolved in the cytosol
Water, proteins, salts, sugars, others
Inclusions
Chemical substances that may or may not be present. Include stored nutrients, glycogen granules, lipid droplets in fat cells , pigment granules in skin and hair
Organelles
Metabolic machinery of cells
Which organelles lack a membrane
Ribosomes and centrioles
Why do membranous organelles need a membrane
To maintain a different internal environment than the surrounding cytosol
Threadlike or lozenge shaped organelles
Mitochondria
Active cells have more clusters of
Mitochondria
Mitochondria
ATP generation for cellular activities
Describe the structure of a mitochondrion?
Two membranes. Inner membrane folds and makes cristae. Folds make contact with matrix. Gel-like substance within the mitochondrion.
Enzymes within matrix break down intermediate products of food fuels (Glucose and others) to water and CO2
Important components of of mitochondria that let them reproduce themselves?
DNA, RNA, ribosomes.
What directs the synthesis of proteins needed for mitochondrial function?
Mitochondrial genes 37 make 1%
Cell’s nucleus makes 99%
Fission
Mitochondria synthesize more cristae or pinch in half to increase their number and then grow their size
Ribosomes
Sites of protein synthesis. Has two subunits. Made of proteins and RNAs
Free ribosomes
Float freely in cytosol.
Make soluble proteins that work in cytosol, as well as those imported into mitochondria and other organelles
Membrane bound ribosomes
Attached to membranes. Form rough ER. Make proteins that are going to be incorporated into membrane or lysosomes or exported out of cell
Crenation
Water goes out of cell because it’s in a hypertonic solution
Endoplasmic reticulum
System of interconnected tubes and parallel sacs called cisterns. Cisterns are filled with fluid
Continuous with outer membrane and accounts for half of the cell’s membranes
ER
Rough endoplasmic reticulum
Studded with ribosomes
Makes proteins that go to golgi apparatus
Functions of rough ER
- Makes secretory proteins. Abundant in antibody producing cells, liver cells. Make blood proteins
- Membrane factory. Integral proteins and phospholipids are manufactured. Makes glycoproteins
Enzymes that catalyse lipid synthesis have their active sites on
External (cytosolic) face of ER membrane where needed substrates are available.
RAS
Most frequently mutated genes in human cancer.
family of genes that regulate cell growth and division. mutations can cause cancer
Myc
