Chapter 3 - Cellular Level Flashcards
What is cell division?
Where one cell divides into two identical cells
What is a cell?
Living structural and functional units enclosed by a membrane
What is the name of cell biology?
Cytology - study of cellular structure and function
What are the three main parts of a cell?
- Plasma membrane
- Cytoplasm
- Nucleus
What is the plasma membrane?
The cell’s flexible outer surface, separating the cell’s internal environment from the external environment
A flexible, sturdy barrier that surrounds and contains the cytoplasm of a cell
What is cytoplasm?
All of the cellular contents between the plasma membrane and the nucleus.
Cytoplasm is divided into what two parts?
- Cytosol - the fluid portion of cytoplasm
2. Organelles - “little organs”, each type has a characteristic shape and specific function
What is the nucleus of a cell?
A large organelle that houses most of the cell’s DNA
Contains chromosomes
What is a chromosome?
A single molecule of DNA associated with several proteins
Contains thousands of hereditary units called genes that control most aspects of cellular structure and function
What is a fluid mosaic model?
The molecular arrangement of the plasma membrane resembles a continually moving sea of fluid lipids that contains a mosaic of many different proteins
What is the basic structural framework of the plasma membrane?
Lipid bilayer
What is the lipid bilayer made up of?
Back-to-back layers made up of:
- Phospholipids
- Cholesterol
- Glycolipids
What are phospholipids?
Lipids that contain phosphorus
What is a cholesterol molecule?
Steroid with an attached OH- group
What is a glycolipid?
Lipid with an attached carbohydrate group
What does amphipathic mean?
Both polar and nonpolar parts
What are integral proteins?
Proteins that extend into or through the lipid bilayer among the fatty acid tails and are firmly embedded in it
What are transmembrane proteins?
They span the entire lipid bilayer and protrude into both the cytosol and extracellular fluid
What are peripheral proteins?
Not as firmly embedded in the membrane
Attached to the polar heads of membrane lipids or to integral proteins at the inner or outer surface of the membrane
What are glycoproteins?
Proteins with carbohydrate groups attached to the ends that protrude into the extracellular fluid
What is the glycocalyx?
An extensive sugary coating on the extracellular surface of the plasma membrane. It is composed of the carbohydrate portions of the membrane, glycolipids and glycoproteins
What are the functions of the glycocalyx?
- enables cells to recognize each other
- enables cells to adhere to each other
- protects cells from being digested by enzymes in the extracellular fluid
- it is hydrophilic, attracts a film of fluid to the surface, makes it slippery
What are ion channels?
Pores or holes that specific ions (K+), can flow into and out of the cell
Most are selective, allow only one type of ion through
What is a carrier?
Transports specific substances across membrane by changing shape
Selectively moves a polar substance or ion from one side of the membrane to the other
Also known as transporters
What are receptors?
Recognizes specific ligand and alters cell’s function in some way
Serve as cellular recognition sites
Each type of receptor recognizes and binds a specific type of molecule
What is a ligand?
A specific molecule that binds to a receptor
What is an enzyme?
A catalyst to speed up specific chemical reactions inside or outside of the cell
What are linkers?
Anchor filaments inside and outside the plasma membrane
Provides structure, stability and shape
Link two cells together
What do cell-identity markers do?
- Recognize other cells of the same kind during tissue formation
- Recognize and respond to potentially dangerous foreign cells
What does a membranes fluidity depend on?
Number of double bonds in the fatty acid tails of the lipids that make up the bilayer and the amount of cholesterol present
Why is the membrane described as selectively permeable?
Allows some substances to pass more easily than others
What is the lipid bilayer permeable to?
To nonpolar, uncharged molecules
(Oxygen, carbon dioxide, steroids )
*impermeable to ions and large, uncharged polar molecules such as glucose
** slightly permeable to small uncharged polar molecules such as water, urea,
What is a concentration gradient?
The difference in the concentration of a chemical from one place to another (such as, inside to outside of a cell)
Give two examples of something that is more concentrated on the outside than inside of the cell.
Oxygen molecules Sodium ions (Na+)
Give two examples of something that is more concentrated on the inside than outside of the cell.
Carbon dioxide Potassium ions (K+)
Which surface of the membrane is more positively charged? Negatively?
Inner surface is more negatively charged
Outer surface is more positively charged
What is the electrical gradient?
The difference in electrical charges between two regions
What is the name for the electrical gradient across a plasma membrane?
Membrane potential
Why is the concentration gradient and electrical gradient important?
It helps move substances across the plasma membrane
A substance will move DOWN its concentration gradient
What is the term for the combined influence of the concentration gradient and the electrical gradient on movement of a particular ion?
Electrochemical gradient
What are passive processes?
A substance moves down its concentration/electrical gradient to cross the membrane using only its own kinetic energy
No input of energy from the cell is required
Example, diffusion
What are active processes?
Cellular energy is used to drive the substance “uphill” against its concentration/electrical gradient
Cellular energy is used (usually ATP)
What is diffusion?
The passive process in which the random mixing of particles in a solution occurs b/c of the particles kinetic energy.
What are some factors that influence the diffusion rate of substances across a plasma membrane?
Steepness of the concentration gradient, higher concentration - faster
Temperature, higher temp - faster
Mass, larger mass - slower
Surface area, more surface area - faster
Diffusion distance, greater distance - slower
What are the three different kinds of diffusion?
Simple, facilitated, osmosis
What is simple diffusion?
Passive process, which substances move freely through the lipid bilayer of the plasma membrane without the help of transport proteins
Nonpolar, hydrophobic molecules move across the lipid bilayer through the process of simple diffusion
What are some example of molecules that move by simple diffusion?
Oxygen, carbon dioxide, nitrogen, fatty acids, steroids, and fat soluble vitamins (nonpolar hydrophobic)
Water, urea, small alcohols (small uncharged polar)
What is facilitated diffusion?
An integral membrane protein assists specific substances across the membrane
Can either be a membrane channel or carrier
This is for substances that are too polar or highly charged to move by simple diffusion
What is channel-mediated facilitated diffusion?
A solute moves down a concentration gradient across the lipid bilayer through a membrane channel
Most are ion channels
Generally slower than simple diffusion
What is carrier-mediated facilitated diffusion?
A carrier (transporter) moves a solute down a concentration gradient across the plasma membrane
Passive process
Solute binds to a specific carrier on one side of the membrane and is released on the other side
What is the transport maximum?
The rate at which facilitated diffusion can occur, depends on the number of carriers available in the plasma membrane
What are some examples of substances that move across the plasma membrane by carrier-mediated facilitated diffusion?
Glucose, fructose, galactose, some vitamins
Describe how glucose enters a plasma membrane.
- Glucose binds to a specific type of carrier protein called the glucose transporter on the outer surface
- Transporter changes shape, glucose passes through the membrane
- Transporter releases glucose on the inside of the membrane
How does insulin affect the diffusion of glucose?
Insulin promotes the insertion of many copies of glucose transporters into the plasma membrane, thus increasing the rate of glucose diffusion
What is the inability to produce insulin called?
Diabetes mellitus
What is osmosis?
A type of diffusion in which there is a net movement of a solvent through a selectively permeable membrane
Passive process
Solvent is water in living systems
Moves from higher WATER concentration to lower WATER concentration
During osmosis, what are the two ways that water molecules can pass through a plasma membrane?
- By moving between neighbouring phospholipid molecules in the lipid bilayer, by simple diffusion
- By moving through aquaporins, integral membrane proteins that function as water channels
When can osmosis only occur?
When a membrane is permeable to water but not permeable to certain solutes
What is hydrostatic pressure?
The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity.
What is osmotic pressure?
The minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane
(Amount of pressure needed to stop the movement of water from the left tube into the right tube)
What is a solutions tonicity?
A measure of the solutions ability to change the volume of cells by altering their water content
What is an isotonic solution?
Any solution in which a cell maintains its normal shape and volume
What is a hypotonic solution?
A solution that has a lower concentration of solutes than the cytosol in the red blood cells.
Water molecules enter the the cells faster than they leave, causing the RBCs to swell and eventually burst
What is hemolysis?
When red blood cells rupture b/c they are placed in a hypotonic solution
What is lysis?
The rupture of any other cells (other than red blood cells) due to being placed in a hypotonic solution
What is a hypertonic solution?
A higher concentration of solutes than does the cytosol inside red blood cells
Water molecules move out of the cells faster than they enter, causing the cells to shrink
What is the name for when cells shrink in size due to a hypertonic solution?
Crenation
Is pure water a hypotonic or a hypertonic solution?
Very hypotonic and causes rapid hemolysis
What is active transport?
An active process where energy is required for carrier proteins to move solutes across the membrane against their concentration gradient
What are the two sources of energy that can be used to drive active transport?
- Energy obtain from hydrolysis of ATP is the source of primary active transport
- Energy stored in an ionic concentration gradient is the source in secondary active transport
What are some example of ions that are actively transported across the plasma membrane?
Na+, K+, H+, Ca+2, I-, Cl-, amino acids and monosaccharides
Describe how primary active transport works.
Energy derived from hydrolysis of ATP changes the shape of a carrier protein, which pumps a substance across a plasma membrane against its concentration gradient.
A typical body cell expends about 40% of its ATP it generates on primary active transport
What is the most prevalent primary active transport mechanism?
The sodium-potassium pump.
Expels sodium from the cells and brings in potassium
What does the sodium-potassium pump do?
Maintains a low concentration of sodium in the cytosol (against its concentration gradient) and maintains a high concentration of potassium in the cytosol (against its concentration gradient)
B/c sodium and potassium slowly leak through the membrane, the pumps must work continuously
What are the 4 steps of the sodium-potassium pump?
- Three sodium ions in the cytosol bind to the pump protein
- Binding of sodium ions triggers the hydrolysis of ATP into ADP (a reaction that attaches a phosphate group to the pump protein). This changes the shape of the protein, expelling 3 sodium ions into the ECF, now the shape favours binding of two potassium ions in the ECF to the pump protein
- Binding of potassium ions triggers the release of the phosphate group from the pump protein, this reaction again causes the pump to change shape
- As the pump reverts to its original shape, it’s releases potassium ions into the cytosol, pump is ready again to bind three sodium ions. Cycle repeats
Why is the sodium-potassium pump so important?
It is crucial for maintaining normal cell volume and for the ability of some cells to generate action potentials from electrical signals.
Helps to maintain normal tonicity on each side of the plasma membrane, ensures that cells don’t shrink or swell
What is secondary active transport?
The energy stored in a Na+ or H+ concentration gradient is used to drive other substances cross the membrane against their own concentration gradient. B/c a Na+ or H+ concentration gradient is established by primary active transport, secondary active transport INDIRECTLY uses energy obtained from the hydrolysis of ATP.
Uses the potential energy of Na+, like water stored behind a dam.
If Na+ can leak back in, stored energy can be converted to kinetic energy and bring other substances across
What is a symporter?
A carrier protein that simultaneously bind to a sodium ion and another substance and then changes shape so that both substances cross the membrane at the same time, this transporter would be called a symporter
What is an antiporter?
When two substances move in opposite directions across the membrane
What is a vesicle?
A small spherical sac
What is endocytosis?
Materials move INTO a cell in a vesicle formed from the plasma membrane
Need energy supplied by ATP
What is exocytosis?
Materials move OUT of a cell by the fusion of the vesicles formed inside the cell with the plasma membrane
Need energy supplied by ATP
What are three different kinds of endocytosis?
- Receptor-mediated endocytosis
- Phagocytosis
- Bulk-phase endocytosis
What is Receptor-mediated endocytosis?
A highly selective type of endocytosis by which cells take up specific ligands (ligands are molecules that bind to specific receptors)
Give a detailed explanation of how receptor-mediated endocytosis works.
- LDL particles that contain cholesterol bonds to a specific receptor in the plasma membrane to form a receptor-LDL complex. The receptors are integral membrane proteins that are concentrated in regions of the plasma membrane called the clathrin-coated pits. Here, a protein called clathrin attaches to the membrane on its cytoplasmic side. Many clathrin molecules come together, forming a basket like structure round the receptor-LDL complexes that causes the membrane to invaginate (fold inward).
- Vesicle formation - the invaginated edges of the membrane around the clathrin-coated pit fuse, and a small piece of the membrane pinches off. The resulting vesicle, known as a clathrin-coated vesicle contains the receptor-LDL complexes
- Uncoating - almost immediately the vesicle loses its clathrin coat to become an unchanged vesicle
- Fusion with endosome - the uncoated vesicle fuses with a vesicle known as an endosome. Within an endosome, the LDL particles separate from their receptors
- Recycling of receptors to plasma membrane - receptors accumulate in transport vesicles that return them to the plasma membrane
- Degradation in lysosomes - LDL particle vesicles fuse with lysosomes that contain digestive enzymes. They break down the large protein and lipid molecules of the LDL particle into amino acids, fatty acids and cholesterol. These small molecules then leave the lysosomes
What is phagocytosis?
A form of endocytosis in which the cell engulfs large solid particles, such as worn-out cells, whole bacteria or viruses
What is the name of cells that are able to carry out phagocytosis?
Phagocytes
What are the two main types of phagocytes?
Macrophages - located in many body tissues
Neutrophils - a type of white blood cell
Describe in detail the process of phagocytosis.
Begins when a particle binds to the plasma membrane receptor on the phagocyte, causing it to extend pseudopods. Pseudopods surround the particle outside of the cell and the membranes fuse to form a vesicle called a phagosome, which enters the cytoplasm. The phagosome fuses with one or more lysosomes, and the lysosomal enzymes break down the ingested material. In most cases, any undigested materials in the phagosome remain indefinitely in a vesicle called a residual body.
What are pseudopods?
Projections of its plasma membrane and cytoplasm
What is contained in a residual body?
Any undigested material in a phagosome remain indefinitely in a vesicle called a residual body. The residual body is then either secreted by the cell via exocytosis or they remain stored in the cell as lipofuscin granules.
What is bulk-phase endocytosis?
A form of endocytosis in which tiny droplets of extracellular fluid are taken up. No receptor proteins are involved. All solutes dissolved in the ECF are brought into the cell.
Describe in detail how bulk-phase endocytosis works.
The plasma membrane folds inward and forms a vesicle containing a droplet of extracellular fluid. The vesicle pinches off from the plasma membrane and enters the cytosol. Within the cell, the vesicle fuses with a lysosome, where enzymes degrade the engulfed solutes. The resulting smaller molecules, such as amino acids and fatty acids leave the lysosome to be used elsewhere by the cell. Occurs in most cells, especially absorptive cells in the intestines and kidneys.
What is exocytosis?
Exocytosis releases materials from a cell.
Where is exocytosis especially important?
- Secretory cells that liberate digestive enzymes, hormones, mucus, and other secretions
- Nerve cells that release substances called neurotransmitters
- in some cases, waste is also released by exocytosis
How does exocytosis work?
Membrane enclosed secretory vesicles called secretory vesicles, form inside the cell, fuse with the plasma membrane and release their contents into the ECF.
