AICE Biology Chapter 4 Review (Cell Membrane)

Phagocytosis

'Cell eating.' This is bulk uptake of solid material. Cells specializing in this are phagocytes. Vacuoles formed are called phagocytes.

Pinocytosis

'Cell drinking.' This is the bulk uptake of liquid. The vacuoles formed are called vesicles.

Explain endocytosis (include the two types).

'Cell eating.' It involves the engulfing of the material by the cell surface membrane to form a small sac, or 'endocytic vacuole.' The two types are phagocytosis and pinocytosis.

The rate of diffusion across the membrane depends on what 4 factors?

1) The steepness of the concentration gradient, that is the difference in the concentration of the substance of the two sides of the surface. 2) Temperature. At high temperatures, molecules and ions have much more kinetic energy. They move around faster, and thus diffusion takes place faster. 3)Surface area of the surface in which diffusion takes place. The greater the surface area, the more molecules or ions can cross it at any one moment; therefore, the faster diffusion can occur. 4) Nature of the molecules or ions. Small and uncharged molecules can get through easily.

What is the role of proteins in the cell membrane?

1. Inter-cellular communication - e.g. receptors for enzymes. 2. Transport: Proteins form transporters or channels, allowing substances to pass into and out of the cell. This can be passively (eg. aquaporins) or actively (the sodium potassium pump) 3. Immune functions - eg. antigens. 4. Structure. Some cells use proteins to maintain complex structures, as the phospholipid bilayer defaults to a simple spherical blob without them (and supporting carbohydrates)

What are the steps to cell signalling?

1.Reception 2.Transduction 3.Response

How wide is the cell membrane?

7 nm

A substance moves into a cell through a protein pore. Which of the following describes this movement? A an ion moving against its concentration gradient by active transport B glucose moving down its concentration gradient by diffusion C oxygen moving against its concentration gradient by facilitated diffusion D carbon dioxide moving against its concentration gradient by osmosis

A

Outline the process of cell signalling involving the release of chemicals that combine with cell surface receptors on target cells, leading to specific responses.

A basic outline involves: Receptors-Transduction-Response. The signal or stimulus is received. The original signal is converted to a message and transmitted in a process called transduction. Transmitting the message involves crossing barriers like the cell surface membrane. The signalling molecules are usually very small for easy transport. A visual image: https://upload.wikimedia.org/wikipedia/commons/a/a4/1Signal_Transduction_Pathways_Model.jpg

What is a hypertonic solution?

A hypertonic solution is a particular type of solution that has a greater concentration of solutes on the outside of a cell when compared with the inside of a cell.

What is a hypotonic solution?

A hypotonic solution is any solution that has a lower osmotic pressure than another solution. In the biological fields, this generally refers to asolution that has less solute and more water than another solution

What is the fluid mosaic model? Why is the model of the cell membrane called the "fluid mosaic" model?

A model that describes the structure of cell membranes. In this model, a flexible layer made of lipid molecules is interspersed with large protein molecules that act as channels through which other molecules enter and leave the cell.

Describe hydrophilic and hydrophobic.

A phospholipid bilayer contains a hydrophilic head and a hydrophobic tail. Hydrophobic tails form the interior of the membrane and help with diffusion. Hydrophilic heads interact with water due to the presence of a phosphate group which is polar, like water.

What is a protoplast?

A plant, bacterial, or fungal cell that had its cell wall completely or partially removed using either mechanical or enzymatic means. In short, it is the living part of the cell. THIS IS NOT IN THE ANIMAL CELL! (http://www.bioparadigma.spb.ru/hidden_history/images/fig01.gif)

Define polar and nonpolar.

A polar molecule has a partial negative and a partial positive charged on separate sides. Since water is also polar, other polar molecules are hydrophilic. In nonpolar molecules, the molecules are hydrophobic.

What is the difference between the solute and solvent?

A solute is the dissolved substance in a solution. A solvent is a liquid substance capable of dissolving other substances.

Explain active transport.

Active transport is the energy-demanding transfer of a substance across a cell membrane against its concentration gradient, i.e., from lower concentration to higher concentration. Special proteins within the cell membrane act as specific protein 'carriers'. The energy for active transport comes from ATP generated by respiration (in mitochondria).

Why is aquaporin needed?

Although water can be diffused over the membrane, it needs aquaporin considerably increase the rate of passage of water.

What is an isotonic solution?

An isotonic solution refers to two solutions having the same osmotic pressure across a semipermeable membrane. This state allows for the free movement of water across the membrane without changing the concentration of solutes on either side.

Why is diffusion more effective with small cells than large cells?

As a cell increases in size, there is less surface area in proportion to its volume. Relatively there is less surface area of cell membrane over which infusion can occur. As the cell grows and increases in size, their surface area - and thus their ability to take in nutrients and transport electrons - does not increase to the same degree as their volume.

A protein is synthesised by a ribosome in an animal cell. What is the sequence of events leading to the secretion of the protein by exocytosis? 1 protein modified by the Golgi apparatus 2 protein enters the endoplasmic reticulum 3 secretory vesicles fuse with the cell surface membrane 4 secretory vesicles formed by the Golgi apparatus 5 vesicles bud off from the endoplasmic reticulum A 1 → 2 → 5 → 4 → 3 B 2 → 5 → 1 → 4 → 3 C 3 → 4 → 1 → 5 → 2 D 5 → 4 → 3 → 2 → 1

B

What is plasmolysis? Describe and explain what happens during it.

Before we explain plasmolysis, let's talk a little about plant cell anatomy. Plant cells have a thick outer wall called a cell wall. The cell wall prevents the plants from losing their shape, and is actually what holds them upright. Beneath the cell wall is the protoplas, the living part of the cell. In the protoplast is a special part called the vacuole, which holds the water in a plant cell, like a water tower. During plasmolysis, the plant doesn't get enough water. The cytoplasm and plasma membrane shrivel up and pull away from the cell wall. This causes the whole plant to wilt. Plasmolysis is the reason plants wilt when they don't get enough water!

Examples of the bulk transport of materials into or out of cells are listed. 1 white blood cell engulfing a bacterium 2 plant cell building up its cell wall 3 pancreas cell releasing digestive enzymes 4 ovum taking up liquid nutrients from a follicle cell Which are examples of exocytosis? A 1 and 2 only B 1 and 4 only C 2 and 3 only D 3 and 4 only

C

Whatare the most abundant molecules in the cell surface membranes of plant cells? A cholesterol B glycolipids C phospholipids D proteins

C

Cholesterol

Cholesterol keeps the membrane fluid consistent. They have hydrophilic heads and hydrophobic tails, so they fit neatly into the phospholipid bilayer. Cholesterol is also important in mechanical stability. Without it, the membrane would burst. The hydrophobic regions help to prevent ions or polar molecules from passing through the membrane.

Explain diffusion.

Diffusion is the net passive movement of particles (Like atoms, ions, and other molecules) from a high to a low concentration. Examples are Osmosis, gas exchange in the alveoli, gas exchange for photosynthesis, gas exchange for respiration, and transfer of transmitter substance.

Cystic fibrosis

Disease in which there is a defect in a protein that normally allows chloride ions to move out of cells, which causes the chloride ions to not move out.

What processes are involved in bulk transport?

Endoctosis, specifically phagocytosis and pinocytosis, and exocytosis.

What do active transport and facilitated diffusion have in common?

Facilitated diffusion and active transport are types of ways to move materials across the cell membrane. They both use protein pumps, specifically carrier proteins, to transport ions, sugar, and salts.

If the concentration difference is zero, then what will be the rate of transport for facilitated diffusion, diffusion, and active transport? Explain.

Facilitated diffusion and diffusion will not occur because they passively transport substances, meaning they go down the concentration gradient. Active transport does not depend on the concentration gradient, so it will keep on going.

What are G proteins?

G proteins are guanine nucleotide-binding proteins. They have three subunits, alpha, beta, and gamma. The alpha subunit has the ability to bind to and hydrolyze guanosine triphosphate (GTP) to guanosine diphosphate (GDP). When bound to GTP, the alpha subunit is 'on' and pull away, leaving the other subunits. This allows the other subunits to interest with other effector molecules.

How are G-proteins involved in growth?

G proteins play a major role in cell-signalling, which deals with regulating cell growth.

What molecule binds to the G protein to turn it on?

GTP

Explain exocytosis.

In exocytosis, materials are exported out of the cell via secretory vesicles. In this process, the Golgi complex packages macromolecules into transport vesicles that travel to and fuse with the plasma membrane. This fusion causes the vesicle to spill its contents out of the cell.

What is another name for intrinsic proteins?

Integral proteins

Importance of cell signalling

It helps organisms respond appropriately to their environment.

The effect of the sodium potassium pump

It is a carrier protein used for active transport that makes the inside more negative than the outside, making a potential difference.

What is a Visking tube also known as? What does it do?

It is also known as a dialysis tube.

What is the role of the sodium potassium pump?

It pumps 3 Na+ ions out of the cell at the same time as allowing 2 K+. This makes the outside positive and the inside negative.

What do solute molecules do to the water potential?

Lower it

Movement of intrinsic proteins

Most float around in the phospholipid layers, but some are fixed in one spot.

If equilibrium is reached, then does diffusion stop?

No, because the molecules in the cell membrane are always moving.

What is osmosis?

Osmosis is a special example of diffusion. It is the diffusion of water through a partially permeable membrane from a more dilute solution to a more concentrated solution - down the water potential gradient) Note: diffusion and osmosis are both passive, i.e. energy from ATP is not used.

What is another name for extrinsic proteins?

Peripheral proteins

What are aquaporins important in and why?

Plant cells need aquaporins for facilitating the symplastic movement of water through the plant and allowing rapid water movement. (Can it relate to keeping turgidity?)

Why does plasmolysis only occur in plant cells?

Plasmolysis can only occur in cells with a cell wall because it prevents the plant from losing its shape; therefore, plasmolysis cannot occur in an animal cell because it has no cell wall. It can also happen in bacteria.

Intrinsic proteins

Proteins embedded in the phospholipid bilayer. They can be found in the inner layer, outer layer, or commonly spanning across the membrane.

What has the highest possible water potential?

Pure water

What are large and/or polar/hydrophilic substances and ions(charged particles) transported through?

Specific ions can be transported through channel proteins by facilitated diffusion. Large and/or polar molecules can be transported through carrier proteins by active transport.

Why are cells small?

The ability for cells to maintain homeostasis by interacting with its environment and itself is very dependent upon its size. When cells are small, they have a low volume and high surface area, which means there is more of the cell membrane that allows molecules to move across. As cells increase in size, the volume increase faster than the surface area, so the surface area-to-volume ratio shrinks and slows the rate of diffusion.

Why is the cell membrane partially permeable?

The cell membrane is described as selectively permeable because it only allows certain materials into the cell.

Facilitated diffusion

The diffusion of a substance through transport proteins in a cell membrane. The proteins provide hydrophilic areas that allow the molecules or ions to pass through the membrane which would otherwise be less permeable.

Why is the cell membrane a critical component for most signalling pathways?

The membrane is a barrier of the movement of molecules, controlling what moves between the external and internal environment of a cell. Usually, molecules have to cross or interact with the cell membrane.

What can move through the lipid bilayer?

The plasma membrane is selectively permeable; hydrophobic/non-polar molecules and small hydrophilic/polar molecules can easily diffuse through the lipid layer, but ions and large hydrophilic/polar molecules cannot. Whether molecules can pass through the membrane depends on its size and its electrical nature. The membrane is highly permeable to non-polar(fat-soluble) molecules.

What happens during incipient plasmolysis?

The point at which pressure potential has just reached zero and plasmolysis is about to occur.

Effect of the size of any 3D object increasing

The surface area:volume ratio decreases

Describe fully what will occur if a plant cell is placed in a solution that has a higher water potential than the cell.

The water on the outside will diffuse into the cell, making it turgid

Describe fully what will occur if a plant cell is placed in a solution that has a lower water potential than the cell.

The water will diffuse out of the cells, making it flaccid. If the solution is very hypertonic, the protoplast shrinks as well as the vacuole. It pulls away from the cell wall, completing plasmolysis.

What are the functions of G proteins?

They regulate metabolic enzymes, ion channels, transporter proteins, and other parts of cell machinery. They act as molecular switches and transmit signals from out of the cell.

Be able to describe, explain, and recognize the fluid mosaic model of the membrane structure.

https://upload.wikimedia.org/wikipedia/commons/d/da/Cell_membrane_detailed_diagram_en.svg

As a result of diffusion...

molecules tend to reach an equilibrium situation where they are evenly spread within a given volume of space.

Which cells have receptors for the hormone insulin?

muscle and liver cells.

The greater the difference in concentration...

the faster the net rate of diffusion

The more unsaturated the phospholipid tails are,...

the more the fluid the membrane.

What are things that can be diffused and why?

-Nonpolar molecules bc they are soluble in the nonpolar phospholipid tails. -Oxygen and carbon dioxide bc they are uncharged and nonpolar -Water molecules. Despite them being polar, they are very small.

What things cannot be diffused and why?

-Polar molecules=insoluble -Glucose and amino acids-->Big -Ions--> charged

What are ways a receptor can alter the activity of a cell, other than through second messengers?

-opening an ion channel, resulting in a change in membrane potential -acting directly as a membrane-bound enzyme -acting as an intracellular receptor when the initial signal passes straight through the membrane.

) investigate the effect of changing surface area to volume ratio on diffusion using agar blocks of different sizes e) investigate the effects of immersing plant tissues in solutions of different water potential, using the results to estimate the water potential of the tissues

...

How do enzymes play a part in cell signalling in the cell membrane?

...

b) investigate simple diffusion using plant tissue and non-living materials, such as glucose solutions, Visking tubing and agar c) calculate surface areas and volumes of simple shapes (e.g. cubes) to illustrate the principle that surface area to volume ratios decrease with increasing size

...

Water potential of pure water

0

What does R in -ICRT stand for?

0.0831

What is the ionization for sucrose?

1

8 characteristics of the fluid mosaic model

1) The membrane is a double layer of phospholipid molecules. 2) The phospholipid tails point inwards, facing each other forming a non-polar hydrophobic interior. The phospholipid heads face the aqueous medium that surrounds the membrane 3) Some of the phospholipid tails are saturated and some are unsaturated. The more unsaturated they are, the more fluid the membrane. This is because the unsaturated fatty acid tails are bent and therefore fit together more loosely. As temperature decreases membranes become less fluid, but some organism which cannot regulate their own temperature, such as bacteria and yeasts, respond by increasing the proportion of unsaturated fatty acids in their membranes. 4) Most of the protein molecules float like mobile icebergs in the phospholipid layers, although some are fixed like islands to structures inside the cell and do not move about. 5) Some proteins are embedded in the outer layer, some in the inner layer and some span the whole membrane. They stay in the membrane because they have hydrophobic portions which sit among the hydrophobic phospholipid tails. Hydrophilic portions face outwards. 6) The thickness of is 7nm 7) Many proteins and lipids have short, branching carbohydrate chains attached to the external surface of the membrane, thus forming and glycolipids respectively. 8) Molecules of cholesterol are also found int he membrane. glycoprotiens

Transmembrane proteins

A common type of intrinsic protein that spans across the whole membrane. In these proteins, the hydrophobic regions which cross the membrane are often made up of >1 a-helical chain.

Define concentration gradient.

A difference in the concentration of a substance across a distance

Which of the following correctly describes the movement of water by osmosis? A from a region of higher water potential to a region of lower water potential through a fully permeable membrane B from a region of higher water potential to a region of lower water potential through a partially permeable membrane C from a region of lower water potential to a region of higher water potential through a fully permeable membrane D from a region of lower water potential to a region of higher water potential through a partially permeable membrane

B

The cells of the myelin sheath are wrapped in layers around nerve cell axons. Freeze-fractured preparations of themyelin sheath cell surface membranes show very few particles. This indicates that myelin membranes contain relativelfyew of which type of molecule? A cholesterol B glycolipids C polysaccharides D proteins

D

Whereare the carbohydrate portions of glycolipids and glycoproteins located in cell surface membranes? A the inside and outside surfaces of the membrane B theinside surface of the membrane C the interior of the membrane D the outside surface of the membrane

D

What is the difference between facilitated diffusion and diffusion?

Facilitated diffusion is the movement of specific molecules down a concentration gradient, passing through a membrane with a specific carrier protein Diffusion is the net passive movement of particles from a high to a low concentration.

Extrinsic proteins

Found on the inner or outer surface of the membrane, many are bound to intrinsic proteins.

Why is bulk transport needed?

It is needed to get large quantities of substances (like proteins, polysaccharides, parts of cells, and sometimes even whole cells) into or out of the cell.

What are micelles?

Micelle are very similar to the phospholipid bilayer. A micelle also is made up of phospholipids with hydrophobic and hydrophilic ends. The difference being that it is composed of a single layer of lipids, no a bilayer. With the membrane of a cell, there is water solution outside and inside with a double lipid layer separating the two. The hydrophobic tails face the interior of the bilayer. The micelle is like a 'solid' sphere with all the hydrophobic tails pointing in and the hydrophilic ends on the surface of the sphere.

What are phospholipids made of and how do the properties of it contribute to its function in the membrane?

Phospholipids are made of lipids with a polar head. Recall that lipids are made of a glycerol attached to three fatty acids. When phosphate is attached to the glycerol, it replaces one of the fatty acids as shown in the picture link. (http://www.uic.edu/classes/bios/bios100/lectf03am/phospholipid.jpg)

Why is cholesterol important in the membrane of the myelin sheath?

This is particularly important in the myelin sheath (made up of many layers of the membrane) around nerve cels, where leakage of ions would slow down nerve impulses.

How can some proteins in the membrane help maintain and decide the shape of the cell?

Some proteins are attached to a system of protein filaments inside the cell, known as a cytoskeleton. This may be involved in changing the cell's shape when the cell moves.

What is the difference between carrier proteins and channel proteins?

Some proteins are transport proteins, transporting molecules or ions across the membrane. They may be either channel proteins or carrier proteins. Channel proteins have a fixed shape and controls ion exchange through opening or closing a part of the inside surface of the protein; carrier proteins can flip between two shapes, allowing one side to open while the other is closed. Channel proteins are used only in facilitated diffusion and transport ions. Carrier proteins transport large and/or polar molecules (maybe also ions) through facilitated diffusion and active transport. They both transport specific substances.

What is the phospholipid bilayer?

The bilayer is a two-layer arrangement of phosphate and lipid molecules to form a cell membrane. There's a polar/hydrophilic head and non-polar/hydrophobic tails made of phosphate

What is the cell membrane made of?

The cell membrane is made of cholesterol, phospholipids, glycolipids, glycoproteins, and proteins.

What are the roles of cell surface membranes (include references to carrier proteins, channel proteins, cell surface receptors and cell surface antigens)

The cell membrane plays vital role in controlling the exchange of materials such as nutrients and waste products between the cell and its environment and the regulation of transport across the cells. They also enable cells to recognize each other and send and receive signals like hormone messages.

Glycolipids and glycoproteins

These structures are proteins or lipids (the heads of phospholipids) with short carbohydrate chains attached to them. They form hydrogen bonds with the water molecules and help stabilize the membrane structure. They are involved in cell-to-cell recognition. They can bind with particular substances like hormones or neurotransmitters.One group of glycoproteins, known as antigens, are important in allowing cells to recognize each other.

What is the characteristic of the most common signalling molecule?

They are water-soluble.

What can hydrophobic signalling molecules do? (Provide examples)

They can diffuse directly across the cell surface membrane and bind to receptors in the cytoplasm or nucleus. Ex: Steroid hormones like estrogen

What is pressure potential?

The force of the cell wall on the contents, • So for animal cells, this is zero, thus, in animals: Water Potential (ψ) = Solute Potential (ψs)

What affects fluidity?

The more unsaturated, the more fluid. The longer the tail, the less fluid. As the temperature decreases, the less fluid.

Diffusion

The net movement of molecules (or ions) from a region of their higher concentration to a region of their lower concentration.

Which regions of an intrinsic protein are hydrophobic or hydrophilic and why?

The region on the inside next to the tails are hydrophobic, which prevents them from repelling each other. The region next to the heads are hydrophilic.

The signalling pathway of water-soluble signalling molecules.

The signal arrives at a protein receptor that matches its specific shape. (Transduction)The signals brings about a change in the shape in the receptor, which causes it to be able to interact with the next component of the pathway. The G protein, which acts as a switch mechanism that activates the release of a second messenger, relays the message until it reaches an enzyme that makes the second messengers, also known as the effector. The second messengers are small, soluble signalling molecules that spread through the cell and greatly amplify the signal. The second messenger typically activates an enzyme, which in turn activates further enzyme, increasing the amplification at each stage. Finally, an enzyme is produced which brings about the required change in cell metabolism.

Explain facilitated diffusion.

This is the movement of specific molecules down a concentration gradient, passing through the membrane via a specific carrier protein. Thus, rather like enzymes, each carrier has its own shape and only allows one molecule (or one group of closely related molecules) to pass through. Selection is by size; shape; charge. Common molecules entering/leaving cells this way include glucose and amino-acids. It is passive and requires no energy from the cell. If the molecule is changed on entering the cell (glucose + ATP → glucose phosphate + ADP), then the concentration gradient of glucose will be kept high, and there will a steady one-way traffic.

What is water potential?

This is the tendency of water to move from one place to another.

What are transport proteins and what do they do?

Transport proteins are pores lined with proteins that are responsible for transporting molecules like ions or large polar molecules across the membrane because of their inability to cross the lipid bilayer.

Define turgor and turgid.

Turgor is the pressure of the swollen cell contents against the cell wall when the external solution more dilute than the cell sap of the vacuole. Turgid is swollen. So, a swollen plan cell.

How do you calculate solute potential?

Using the formula icrt

What is called the universal solvent?

Water

What is the formula for water potential?

Water potential=solute potential+pressure potential

What is micropinocytosis?

When liquid is taken in through the vesicles and form extremely small vesicles.

An example of exocytosis you need to know

When secretory vesicles from the Golgi body carry enzymes to the cel surface and release their contents.

What is the difference between the cell membrane and the cell wall?

While the cell wall and cell membrane surround the cell, they are very different. The cell wall's thickness is measured in micrometers, and the cell membrane is measured in nanometers. The cell wall covers the cell membrane and is also known as the plasma membrane. The cell membrane is present in almost all types of cells while the cell wall is present in bacteria, fungi, algae and plant cells. It is absent in an animal cell and protozoa. The cell wall is freely permeable. The cell membrane is a biological membrane, which is semi- permeable. It allows the passage of certain substances through them. The cell wall contains cellulose in plants and peptido glycans/murein in prokaryotes, strengthening material, or a polysaccharide. The cell membrane is made of phospholipids, protein, and sometimes cholesterol. The cell wall is used for mechanical(physical) strength and structure. The cell membrane is a selective barrier. The cell wall is rigid while the cell membrane is fluid.

Glycolipids and glycoproteins sometimes act as...

antigens, also known as cell markers. For example, the ABO blood group antigens are glycolipids and glycoproteins.

Proteins involved in active transport have...

receptor sites for ATP on its inner surface. It acts as an ATPase, turning ATP into ADP>

What is the symbol for water potential?

Ψ

What is solute potential?

Ψ s. The component of water potential that is due to the presence of solute molecules. It always has a negative value since solutes lower the water potential of the system.

What are major examples of diffusion in biology?

• Gas exchange at the alveoli — oxygen from air to blood, carbon dioxide from blood to air. • Gas exchange for photosynthesis — carbon dioxide from air to leaf, oxygen from leaf to air. • Gas exchange for respiration — oxygen from blood to tissue cells, carbon dioxide in opposite direction. • Transfer of transmitter substance — acetylcholine from presynaptic to postsynaptic membrane at a synapse. • Osmosis — diffusion of water through a semipermeable membrane.

How does turgor play a role in plants?

• Mechanical support for soft non-woody tissue, e.g., leaves. • Change in shape of guard cells forming the stomatal opening between them. • Enlargement of young immature plant cells to mature size.