2.2 Why is CF mucus so sticky?

Question 1

Why is cf mucus sticky?

Answer 1

contains less water than normal.
reduced water level due to abnormal salt and water transport across the cel surface membranes caused by a faulty transport protein channel in the membrane.

Question 2

Amino acid

Answer 2

The basic unit or monomer from which proteins are formed. There are twenty different amino acids which may be linked by condensation to form proteins. All of these amino acids have the same basic chemical structure.

central carbon atom bonded to an amine group (NH2), a carboxylic acid group (COOH), a hydrogen and a residual group.

Question 3

Primary structure

Answer 3

The sequence of amino acids in a protein or polypeptide is known as the primary structure. The primary structure will determine how the polypeptide will fold. There are twenty different amino acids and they can be combined in different ways to produce many different proteins.

Question 4

Peptide bond

Answer 4

The bond joining two amino acids in a protein. Amino acids join together by condensation. When a protein is digested, the peptide bonds are broken down by hydrolysis.

Question 5

Dipeptide

Answer 5

A molecule that is made up of two amino acids joined by a peptide bond.

Question 6

Secondary structure

Answer 6

The alpha-helices and beta- pleated sheets that form when the chain of amino acids in a protein or polypeptide initially folds into a 3D shape. The sequence of amino acids in the chain determines how the chain will twist and fold.

Question 7

Tertiary structure

Answer 7

The 3D structure of a protein. A polypeptide is a molecule made from a large number of amino acids joined by condensation. This polypeptide is folded to form a protein. Some sections of the polypeptide coil and fold to produce the secondary structure of the protein. The whole protein then folds into a specific 3D shape known as the tertiary structure. The tertiary structure of a protein is very important in determining its function.

Question 8

R group bonding

Answer 8

• polar r groups attract other polar molecules like water so are hydrophilic. The non polar groups are hydrophobic.
• Non polar groups face inside protein excluding water from the centre of the molecule
• disulphide bond with r groups that contain -SH like cysteine
• ionic bonds formed
• both are stronger that hydrogen bonds, but sensitive to changes in pH

Question 9

conjugated proteins

Answer 9

They have another chemical group associated with their polypeptide chain e.g haemoglobin associated with iron

Question 10

quaternary structure

Answer 10

Proteins with more that one polypeptide chain have this structure

Question 11

Globular protein

Answer 11

A protein where the polypeptide chain is folded into a compact spherical shape.

• soluble due to hydrophilic side chains
• enzymes, antibodies

Question 12

Fibrous proteins

Answer 12

A protein that is un-folded, often with several polypeptide chains cross-linked together for additional strength.

• insoluble
• structural molecules
• keratin in hair+ skin, collagen in skin

Question 13

Bilayer

Answer 13

Membranes within cells contain two layers of phospholipids and so are said to exist as bilayers.

Question 14

Phospholipid

Answer 14

A phospholipid molecule is a lipid with two distinct sections. It has a head region consisting of glycerol and a phosphate group. This part of the molecule is attracted to water. The other end consists of two fatty acid tails. This end of the molecule repels water. Phospholipids are important components of cell membranes where they are arranged in a bilayer with the heads pointing outwards and the tails pointing towards each other.

Question 15

Glycoprotein

Answer 15

A protein molecule with a polysaccharide attached.

Question 16

Glycolipid

Answer 16

A molecule consisting of a lipid and a carbohydrate. They form part of the cell surface membrane. They have similar functions to glycoproteins; for example, they help cells to bind to each other to form tissues

Question 17

Fluid mosaic model

Answer 17

A theory that describes the structure of the cell membrane as a fluid phospholipid bilayer containing proteins that function as, for example, enzymes, receptors or carriers. These can be integral proteins that are embedded in the membrane, or peripheral proteins located on the surface of the membrane.

Question 18

Integral protein

Answer 18

Proteins that form part of the cell membrane. They are embedded within the phospholipid bilayer and may span the membrane. They may not be fixed within the membrane and can move in the fluid phospholipid bilayer.

Question 19

peripheral protein

Answer 19

loosely attached on the outside surface of the membrane

Question 20

how do substances pass through cell membranes?

Answer 20

• diffusion
• osmosis
• active transport
• exocytosis
• endocytosis

Question 21

Diffusion, Diffuse

Answer 21

The movement of molecules from where they are in a high concentration to where they are in a lower concentration. Small molecules such as oxygen diffuse through cell membranes into cells. Other molecules cross cell membranes with the aid of proteins. This form of diffusion is called facilitated diffusion. Osmosis is a special form of diffusion involving water molecules.

Question 22

Facilitated diffusion

Answer 22

Diffusion is the movement of a substance from where it is in a high concentration to where it is in a lower concentration. Large molecules and ions can only cross cell membranes with the aid of carrier proteins. This form of diffusion is called facilitated diffusion.

Question 23

Channel protein

Answer 23

A protein that spans a membrane and is involved in the transport of molecules across the membrane.

Question 24

Potential difference

Answer 24

The voltage between two points. The voltage is a measure of the change in energy of an electric charge as it moves between those two points.

Question 25

Gated channels

Answer 25

Channel proteins across membranes that can be opened or closed to allow or prevent transport across the membrane. They are controlled by signal proteins or change in potential difference.

Question 26

Passive transport

Answer 26

Movement of substances in a cell or organism without the expenditure of energy

Question 27

Osmosis

Answer 27

Osmosis is a special sort of diffusion. It is the movement of water from a weak solution with a low concentration of solute molecules, to a solution with a higher concentration of solute molecules, through a partially permeable membrane.

Question 28

Active transport

Answer 28

A process that involves the movement of substances from where they are in a low concentration to where they are in a higher concentration; in other words, it involves the movement of substances against a concentration gradient. Active transport involves the use of specific carrier proteins in cell membranes. It also requires energy in the form of ATP.

Question 29

ATP, Adenosine triphosphate

Answer 29

Adenosine triphosphate (ATP) is an important molecule found in all living cells. It is involved in the transfer of energy. Most of the ATP in a cell is produced from ADP and phosphate using energy transferred during the process of respiration. When ATP is broken down, ADP and phosphate are produced and a small amount of energy is made available. This energy may be used: in active transport; to synthesise large molecules such as proteins from smaller ones such as amino acids; and for movement in cells such as sperm and muscle cells.

Question 30

ADP, Adenosine diphosphate

Answer 30

Adenosine diphosphate (ADP) is produced when a phosphate group is removed from ATP. Energy can be transferred from this reaction to do useful work in the cell.

Question 31

Endocytosis

Answer 31

A process which involves the transport of large particles or fluids into cells. The cell surface membrane surrounds the particles concerned. A vesicle is pinched off from the membrane and moves into the cytoplasm of the cell.

Question 32

Exocytosis

Answer 32

A process which involves the transport of substances out of cells. Proteins made in a cell are often modified in the Golgi apparatus. Vesicles are pinched off from the Golgi apparatus and these contain the modified protein. The vesicles move through the cytoplasm and fuse with the cell surface membrane, releasing the protein from the cell.

Question 33

Viscosity

Answer 33

A measure of a fluid’s resistance to flow. Fluid with a high viscosity will flow more slowly due to friction within the liquid.

Question 34

CFTR protein

Answer 34

The channel protein whose malfunctioning causes cystic fibrosis.

Question 35

Excess water in mucus

Answer 35

1. Na+ is actively pumped across the basal membrane
2. Na+ diffuses through sodium channels in the apical membrane
3. Cl- diffuses down electrical gradient
4. Water is draw out of cells by osmosis due to the high salt concentration in the tissue fluid
5. Water is draw out of the mucus by osmosis

Question 36

Too little water in the mucus

Answer 36

1. Cl- is pumped into the cell across the basal membrane
2. Cl- diffuses through the open CFTR channels
3. Na+ diffuses down the electrical gradient into the mucus
4. Elevated salt concentration in the mucus draws water out of the cell by osmosis
5. Water is drawn into the cell by osmosis

Question 37

Why cf lungs cannot regulate the water in mucus

Answer 37

1. CFTR channel is absent or not functional
2. Na+ channel is permanently open
3. Water is continually removed from mucus by osmosis

Question 38

Carrier protein

Answer 38

A protein that binds with a
specific ion or molecule and helps it cross a
membrane.

Question 39

Isotonic

Answer 39

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