PP 5

Question 1

The cell, regardless of all size, has:

Answer 1

1. Stable blueprints of information in molecular form (DNA)
2. A discrete boundary that separates the interior of the cell from its exterior environment
3. The ability to harness materials and energy from the environment (ie photosynthesis and cellular respiration)

Question 2

Function of cell MEMBRANE/ plasma

Answer 2

• Physically separates the outside and the outside of the cell
• Creates compartments within the cell (organelles, vacuoles, vesicles). ONLY IN EUKARYOTES. Archeae and bacteria have no internal membranes

Question 3

What are the ingredients of the cell membrane?

Answer 3

• lipids
• carbohydrates (as part of glycolipids and glycoproteins)
• proteins

Question 4

What are membranes composed of?

Answer 4

Phospholipids! They are composed of hydrophilic (head) and hydrophobic parts (legs)

• micelle: has a hydrophobic interior
• bilayer: has a hydrophobic interior
• liposome: hydrophilic interior

Question 5

Phospholipids that form cell membranes can:

Answer 5

• turn on their axis
• move laterally in any direction over the surface of the membrane
• flipping across the membranes (inside out)

Question 6

The fluidity of a cell membrane can be influenced by:

Answer 6

(1) the type of fatty acid:
- increasing the number of saturated fatty acids, decreases the fluidity because the tails pack easily

• increasing the number of unsaturated fatty acids, increases the fluidity because the “kinks” prevent tight packing
  (2) The presence of cholesterol:

[cholesterol is amphipathic (contain hydrophilic and hydrophobic part)]

It helps maintain the integrity of membranes:
-prevents the phospholipids forming the membrane from moving apart too much (to become more fluid) would resist in things inappropriately entering the cell, especially when temp increases.

• prevents the phospholipids forming the membrane from clumping if temp decreases.

Question 7

Internal membrane proteins

Answer 7

• they extend from the outside to the inside of the membrane
• composed of 3 regions: 2 hydrophilic and 1 hydrophobic
• permanently associated with the cell membrane
• they can be a single pass (pass through once) or multi pass (has many passes)
• the a-helix of the protein is stuck in the cell membrane. The R groups of the amino acid in this region are hydrophobic

Question 8

3 types of internal membrane proteins

Answer 8

1. Uniport (one way)
2. Symport (multiple can go the same way)
3. Antiport (can go in both directions)

Question 9

Cell membrane carbohydrates:

What are glycolipids and glycoproteins?

Answer 9

• membrane bound carbohydrates are involved in cell to cell recognition. Cells recognize the other cell by binding to their molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane.
• Glycolipids: carbohydrates covalently bonded to lipids
• Glycoproteins: carbohydrates covalently bonded to proteins

Question 10

The plasma membrane function:

Answer 10

• Separates the inside from the outside part of the cell
• Maintains homeostasis (the active maintenance of a content envierment)
• Acts as a selective barrier by carefully controlling which molecules enter and leave the cell.

Question 11

What are the 2 types of movements of molecules through a membrane?

Answer 11

1. Passive transport
   - this means that no energy (other the kinetic energy) is invested in order to move molecules in or out of the cell
   - Diffusion and osmosis
2. Active transport
   - Energy in the form of ATP must be used in order to move molecules against a gradient. Does not involve diffusion and osmosis

Question 12

What is diffusion?

Answer 12

Its the movement of a solute down its concentration gradient. Sample diffusion occurs when solutes can pass freely through a permeable membrane without the aid of a protein. Facilitated diffusion requires specific protein to enable most solutes to cross the membrane. Solute moves from high solute concentration to low solute concentration.

• Only lipids, O2, CO2 and N2 can cross the plasma membrane unaided
• NOTE: the ability to cross the membrane decreases with polarity and size. These can pass only with the aid of membrane proteins.

Question 13

What are the 2 types of transport proteins?

Answer 13

Carrier proteins: attach to a specific solute, and this attachment induces the change of shape in a protein, causing it to carry the solute across the membrane and realize on the other side.

Channel proteins: small tubes which allow specific solutes to pass to the other side.

Question 14

Facilitated diffusion

Answer 14

• only kinetic energy is involved, as the movement of solute is down its concentration gradient.
• Unlike lipids and gases like O2 and CO2, many polar molecules, large molecules and ions cannot pass freely through the plasma membrane. This includes water, sugars, salt (ions), which require integral membrane proteins to help them through.

Question 15

What is osmosis?

Answer 15

Its a specific situation of diffusion, but its the movement of water down its concentration gradient

• water molecules move from an area of low solute (high concentration of water) to a high solute (low concentration of water)
• Water molecules cross the cell membrane through a special channel protein called aquaporins.

Question 16

What does active transport require?

Answer 16

It requires energy! Energy:

• causes change
• performs work
• moves/changes matter in a direction that it would not spontaneously undertake

Question 17

What is the energy within a biological system?

Answer 17

ATP (adenosine triphospahte) is the molecular unit of currency of intracellular energy transfer. ATP is chemical potential energy. The hydrolysis of the phosphodiester bonds provides the energy to do cellular work. One form of cellular work is generation an electrochemical gradient across a membrane.

An example of this is moving Na+ across a membrane against its concentration gradient. This is called primary active transport and involves the direct hydrolysis of ATP.

Question 18

What is the fluid mosaic model?

Answer 18

It describe the cell membrane.

• it is fluid because the phospholipids, many proteins and cholesterol can move in the plane of the membrane (like skaters on an ice rink).
• it is a mosaic because of the different proteins, glycoproteins and glycolipids embedded within the membrane (it looks like a mosaic). There are hundreds of different types of proteins on the membrane surface.

Question 19

Primary Active Transport

Answer 19

• Energy is used directly to move solute from a low concentration to a high concentration (against the chemical gradient)
• it is used to move molecules like glucose, animo acids, nucleotides and ions across the plasma membrane, against a gradient.
• When primary active transport move ions, it creates an “electrochemical gradient”, which stores potential energy.
• the potential energy created in the form of an electrochemical gradients could be used by nerve cell to conduct a signal, by muscles to contract or for secondary active transport.

Question 20

Secondary active transport

Answer 20

Its the transport of a solute against its concentration gradient as it is coupled to the facilitated diffusion of a second solute (usually an ion) which is moving down its concentration gradient.

Question 21

Summarize primary and secondary active transport

Answer 21

Primary: uses ATP to generate a concentration gradient between the inside and outside of the cell. [ Primary active transports creates an electrochemical (charge) gradient using ATP directly. This is one form of potential energy. ]

This potential energy can be used to do move solutes against their concentration gradient without directly using ATP.

Secondary: uses the Na+ gradient made by primary. Glucose and galactose are more concentrated inside the cell, so they need help to be carried into the cell. Voilà! There is loads of Na+ around, just waiting to go down its concentration gradient. It’s like hitch hiking. The hitch hiker takes a ride, but has not invested anything in the maintenance of the car!

Question 22

Where is the cell wall located?

Answer 22

it is found outside of the plasma membrane of prokaryotic cells as well as those of plant and fungi cells.

Question 23

What is the function of a cell wall in plants?

Answer 23

1. provides structural support and protection
2. it resists expansion and allows pressure (turgor pressure) to build up in a cell when it absorbs water.

[Turgor pressure: force exerted by water pressing against an object]

3.provides structural support, e.g., plant cells whose vacuoles are as full of water as they can be, are plump.

Question 24

The structure of a cell wall

Answer 24

Rigid structure made mostly of carbohydrates that surrounds the plasma membrane:

• plant cell wall: polysaccharides (cellulose)
• fungi cell wall: polysaccharides (chitin)
• Bactria cell wall: peptidoglycan (has sugars and amino acids)

Question 25

The structure of a cell wall

Answer 25

Rigid structure made mostly of carbohydrates that surrounds the plasma membrane:

• plant cell wall: polysaccharides (cellulose)
• fungi cell wall: polysaccharides (chitin)
• Bactria cell wall: peptidoglycan (has sugars and amino acids)

Question 26

What is the function of a cell wall in plants?

Answer 26

1. provides structural support and protection
2. it resists expansion and allows pressure (turgor pressure) to build up in a cell when it absorbs water.

[Turgor pressure: force exerted by water pressing against an object]

3.