Chapter 3: Cells Flashcards
What is a cell?
This is a living structural and functional unit enclosed by a membrane
What are the three main parts of a cell?
Plasma membrane
Cytoplasm
Nucleus
Describe the structure of the plasma membrane
This makes the cell’s flexible outer surface, which separates the internal and external environment
It is made up of a lipid bilayer which itself is made up of (2x) phospholipids, cholesterol, and glycolipids
What are the two types of proteins in the plasma membrane?
Integral and peripheral
What are the roles of the plasma membrane?
Regulates flow of materials in and out of the cell
Key role in communication among cells and between cells in external environment
What are integral proteins?
These are proteins that extend through the lipid bilayer. These proteins allow small and medium-sized water-soluble materials to cross through the membrane
What are peripheral proteins
These are proteins that loosely attach to the exterior or interior surface of the membrane
How is the plasma membrane selectively permeable?
The lipid bilayer is permeable to water and non-polar molecules like fatty acids, O2, CO2, etc. but is impermeable to ions and large, uncharged polar molecules like glucose and amino acids.
Large molecules like proteins usually require transport via vesicles to travel through the plasma membrane
What are the proteins in the plasma membrane that determine the membrane’s function?
Receptors
Ion channels
Carrier proteins/transporters
Enzymes
Cell identity markers
What is cholesterol used for in the plasma membrane?
This binds with adjacent phospholipids to help make the phospholipid bilayer stronger
It also maintains fluidity in cell membranes at normal body temperatures
What is extracellular fluid? Give some examples
This is the fluid outside of cells. This includes interstitial fluid, blood plasma, and lymph
What is interstitial fluid?
This is a type of extracellular fluid found between cells in tissues
What is blood plasma?
This is a type of extracellular fluid found in blood vessels
What is lymph?
This is a type of extracellular fluid found in lymphatic vessels
What are the methods for which substances move across the plasma membrane?
Passive transport and active transport
What is passive transport?
This is when a substance moves down its concentration gradient through the membrane, only using its own kinetic energy.
Simple diffusion and osmosis
What is active transport?
This is when a substance is pushed through the membrane against its concentration gradient. This requires cellular energy, usually from ATP
Define diffusion
This is a passive process in which a substance will move due to its kinetic energy, travelling from high concentration to low concentration
What is simple diffusion?
This is when substances diffuse across a membrane through the lipid bilayer.
What is facilitated diffusion
This is when a substance can’t move through the membrane via simple diffusion or a passive process.
An integral membrane protein helps the substance move across the membrane. The protein will be either a membrane channel or carrier
Describe the facilitated diffusion of potassium ions
Gated ion channels are present in the plasma membrane that allows intracellular K+ ions to move out into the cell (following concentration gradient) when the gate is open.
Describe the facilitated diffusion of a glucose molecule
The glucose transporter, the carrier protein, is an integral protein which teeters back and forth. In one position, the carrier protein is open to the extracellular fluid, where glucose can onto slots of the carrier protein. The protein will undergo a change in shape, causing it to open to the intracellular fluid, allowing glucose to enter the cell, following its concentration gradient
Describe how water moves in osmosis
Water will move from an area of higher water concentration to an area of lower concentration. Or it will move from an area of lower solute concentration to higher solute concentration.
Describe what will happen next in this experiment:
A selectively permeable membrane that permits water but not sucrose molecules to pass is filled with a 20% sucrose 80% water solution. The upper part of the cellophane sac is wrapped tightly about a stopper through which a glass tube is fitted.
The sac is placed into a beaker containing 100% water
Because the cellophane is selectively permeable to water only, the amount of sucrose inside the sac will not change, but water from the beaker will move into the cellophane because of the higher solute concentration in the sac. Volume in the sac will increase, while the volume of water in the beaker itself will drop
What is an isotonic solution?
This is when the concentrations of solutes are the same on both sides of a membrane.
Any solution in which cells maintain their normal shape and volume is called an isotonic solution
What is a hypotonic solution?
This is a solution that has a lower concentration of solutes, thus a higher concentration of water.
What is a hypertonic solution?
This is a solution that has a higher concentration of solutes, thus a lower concentration of water.
What is osmotic pressure?
This is the pressure that a solution containing solute particles that are impermeable to a membrane exerts on that membrane
If a red blood cell is placed in a hypotonic solution, what will happen to the cell?
Because the solute concentration is higher in the cell, water will flow into it, causing hemolysis
If a red blood cell is placed in a hypertonic solution, what will happen to the cell?
Because the solute concentration is higher in the solution, water will be drawn out of the cell, causing crenation.
How does ATP facilitate active transport?
The energy derived from splitting ATP changes the shape of a carrier protein called a pump, causing the substance to move across a membrane against its concentration gradient
Describe the steps of the sodium potassium pump
3 Na ions from the cytosol will bind to the inside surface of the Na-K pump, triggering ATP to bind as well
ATP is split into ADP and phosphate, with the energy release causing the pump to change shape, moving Na outside of the pump. Phosphate will bind to the inner side of the pump at the same time.
2 K ions from extracellular fluid will bind on the outside surface of the pump and cause the Phosphate from earlier to be released
The release of Phosphate causes the pump to return to its original shape, moving K into the cell
What is a vesicle?
This is a small round sac that is made from existing membrane that buds off
What is endocytosis?
This is when materials move into the cell via vesicle formation from the membrane
What is exocytosis?
This is when materials move out of the cell by fusion of a vesicle with the membrane
What are the types of endocytosis?
Phagocytosis and bulk-phase endocytosis (pinocytosis)
What is phagocytosis?
This is when large solid particles like bacteria, viruses, or dead cells, are taken in by the cell
What is bulk-phase endocytosis or pinocytosis?
This is also known as “cell drinking,” and is when cells take up tiny droplets of extracellular fluid
What are the steps of phagocytosis?
A particle binds to a plasma membrane receptor
Projections of the plasma membrane called pseudopods extend from the cell and surround the particle
Ends of the pseudopods fuse together to form a vesicle called a phagosome that then enters the cytoplasm
The phagosome fuses with one or more lysosomes, which contain lysosomal enzymes that break down the ingested material
Undigested material may remain indefinitely in a vesicle called a residual body, or be exerted by the cell
What is a residual body in a cell?
This is a vesicle that contains undigested material that has been phagocytosed
What is the purpose of pinocytosis?
This is done to extract solutes dissolved in extracellular fluid. Cells are able to extract amino acids and fatty acids in this way
Which molecules are capable of simple diffusion?
Because they need to cross the plasma membrane easily, they must be lipid-soluble molecules.
Oxygen
Carbon dioxide
Fat soluble vitamins like A, D, E, and K
The polar molecules water and urea are capable of simple diffusion
Which molecules undergo facilitated diffusion
ions such as K, Cl, Na, and Ca
Simple sugars such as glucose, fructose, and galactose
Some vitamins
Which substances undergo active transport?
Ions such as Na, K, Ca, H, I, and Cl
Which substances undergo phagocytosis?
Bacteria, viruses, and aged or dead cells
Which substances undergo pinocytosis or bulk-phase endocytosis
Solutes in extracellular fluid
Which substances undergo exocytosis?
Neurotransmitters
Hormones
Digestive enzymes
What is the cytoskeleton of a cell for?
This provides structural framework and generates movements
What is the cytoskeleton comprised of?
This is made of a network of 3 different types of protein filaments
Microfilaments
Intermediate filaments
Microtubules
What is the cytoplasm?
This is everything in the cell except for the nucleus. It includes the cytosol and the organelles
Describe microfilaments
These are the thinnest elements of the cytoskeleton. They make up microvilli which are key for absorption.
Microfilaments are also involved in muscle contraction, cell division, and cell locomotion.
Name some microfilament-assisted movements
Migration of embryonic cells during development,
Invasion of tissues by white blood cells to fight infection
Migration of skin cells during wound healing
Describe intermediate filaments
These are thicker than microfilaments and thinner than microtubules. They are found in areas of the cell subject to tension, like stretching.
They help hold organelles like the nucleus in place
And they help attach cells to one another
Describe Microtubules
These are the largest cytoskeletal component. They are long hollow tubes that help determine cell shape and function for movement of organelles within a cell (like secretory vesicles) and migration of chromosomes during cell division.
They are also responsible for movements of cilia and flagella
What are organelles?
These are specialized structures in cells that have characteristic shapes and functions
What is the centrosome?
This is an organelle near the nucleus.
What is the centrosome made of?
It is made from two centrioles and pericentriolar materials.