Membranes,Proteins,DNA and Gene Expression

Question 1

Describe the fluid mosaic model.

Answer 1

The term ‘fluid’ describes how
individual phospholipid and protein molecules move around within their monolayer. The word ‘mosaic’ describes the pattern produced by scattered protein molecules when the surface of the membrane is viewed from above.

Question 2

Describe the term phospholipid.

Answer 2

The hydrophilic head contains a
phosphate group and glycerol, while the hydrophobic tail contains 2 fatty acid chains. This is due to the negative charge on the phosphate group that gets attracted to the positive charge on the hydrogen atom of the water molecule.

Question 3

What is the phospholipid bilayer?

Answer 3

This provides the basic structure of

membranes; it is selectively permeable and acts as a barrier to most water-soluble substances.

Question 4

Describe the phospholipid bilayer.

Answer 4

The more unsaturated the tails, the more fluid the membrane as unsaturated fatty acid tails are bent and therefore fit together more loosely.
The longer the tail, the less fluid the membrane

Question 5

Describe the term micelle.

Answer 5

Phospholipid molecules that arrange themselves in a spherical form in cross section aqueous solutions.

Question 6

What is the role cholesterol in a cell membrane?

Answer 6

Regulates the fluidity of membranes. Its

hydrophobic region prevents polar molecules from passing through the membrane.

Question 7

What is simple diffusion?

Answer 7

The net movement of molecules or ions from a region of high concentration to a region of low concentration, down the concentration gradient.

Question 8

What is facilitated diffusion?

Answer 8

The net movement of molecules
down the concentration gradient. Molecules go through channel proteins or carrier proteins instead of passing through phospholipids. This allows for the passage of large polar ions and molecules.

Question 9

Does Passive transport require ATP energy?

Answer 9

No.

Question 10

What is Fick’s Law of Diffusion?

Answer 10

(Surface Area x Difference in Conc.)/Thickness of Exchange Surface

Question 11

Simple diffusion and facilitated diffusion are examples of what type of transport?

Answer 11

Passive Transport.

Question 12

What is active transport?

Answer 12

Involves the use of carrier proteins to

move substances against the concentration gradient using ATP energy.

Question 13

What is exocytosis?

Answer 13

The bulk movement of substances from

inside the cell to the outside using vesicles. Vesicles fuse with the cell membrane and release their contents.

Question 14

What is endocytosis?

Answer 14

The bulk movement of substances from

outside the cell to the inside using vesicles formed by the cell membrane.

Question 15

What is osmosis?

Answer 15

The diffusion of water molecules down a water potential gradient through a permeable membrane.

Question 16

What is an isotonic solution?

Answer 16

The concentration of solute on both

sides is equal.

Question 17

What is a hypotonic solution?

Answer 17

The concentration of solute in the solvent is less than the cell.

Question 18

What is a hypertonic solution?

Answer 18

The concentration of solute in the

solvent is more than the cell.

Question 19

Describe osmosis in an animal cell.

Answer 19

1. Pure water or dilute solution(low concentration of solute molecules)-red cell bursts.
2. Solution with same concentration as red cell-red cell remains normal.
3. Concentrated solution(high concentration of solute molecules)-red cell shrinks.

Question 20

What is a protoplast?

Answer 20

The living part of the cell inside the cell

wall

Question 21

Describe osmosis in plant cells, in pure water.

Answer 21

Water enters the cell by osmosis, and

the cell wall pushes back against the expanding protoplast, building up pressure rapidly, becoming turgid.

Question 22

Describe how osmosis occurs in plant cells, in a concentrated solution.

Answer 22

Water will leave the cell by osmosis. The protoplast gradually shrinks until it is exerting no pressure on the cell wall. The protoplast continues to shrink and pull away from the cell wall, so the cell is plasmolysed (incipient plasmolysis).

Question 23

Describe the first stage of plasmolysis.

Answer 23

turgid cell
Cell wall-freely permeable
Cell surface membrane-partially permeable
Tonoplast-partially permeable

Question 24

Describe the second stage of plasmolysis.

Answer 24

Protoplast is starting to shrink away from the cell wall-cell is beginning to plasmolyse.

Question 25

Describe the last stage of plasmolysis.

Answer 25

fully plasmolysed cell
External solution has passsed through the cell call and is still in contact with the protoplast.
Protoplast has shrunk away from the cell wall-the cell is fully plasmolysed.

Question 26

Describe the gross structure of lungs.

Answer 26

Lungs are in chest cavity surrounded by the pleural membranes, which enclose an airtight space. This space contains a small quantity of fluid to allow friction-free movement as the lungs are ventilated by the movement of the diaphragm and ribs.

Question 27

Describe the bronchioles.

Answer 27

Bronchioles are surrounded by smooth muscle, which can contract or relax to adjust the diameter of these tiny airways due to the absence of cartilage. During exercise, the muscles relax to allow a greater flow of air to the alveoli.

Question 28

What is cartilage?

Answer 28

It is a connective tissue. It keeps airways in trachea and bronchi open and air resistance low and prevents them from collapsing or bursting as the air pressure changes during breathing.

Question 29

Describe the epithelium.

Answer 29

Air flows down the lungs through trachea and bronchi, which are lined by cells adapted to remove particles from the air before it reaches the lungs. These
cells make up a tissue called epithelium.

Question 30

What are the two types of epithelium?

Answer 30

Ciliated cells

Goblet cells

Question 31

What are ciliated cells?

Answer 31

They are responsible for the continual movement of mucus towards the larynx.

Question 32

What are goblet cells?

Answer 32

Secretes mucus that traps pathogens,

which are then moved out with the help of cilia.

Question 33

Describe large surface area as an adaption for efficient gas exchange.

Answer 33

A large number of alveoli is present to

increase the surface area

Question 34

Describe the thin surface as an adaptation for efficient gas exchange.

Answer 34

The wall of the alveolus is very thin

(single layer of squamous epithelium) to decrease the diffusion distance. Also, the walls of the capillaries are thin.

Question 35

Describe steep concentration gradient as an adaption for efficient gas exchange.

Answer 35

Deoxygenated blood is brought to the alveoli which provides a steep
concentration gradient for diffusion

Question 36

Describe moist surface as an adaption for efficient gas exchange.

Answer 36

Allows the dissolving of gases.

Question 37

Describe ventilation as an adaption for efficient gas exchange.

Answer 37

Replacing alveolar air with air from

outside the body. This helps maintain the diffusion gradient.

Question 38

Describe the term ‘enzyme’.

Answer 38

Biological catalyst that accelerates
metabolic reactions. Enzymes are globular proteins as they have a roughly spherical shape and are water-soluble. Enzymes functioning inside a cell are
intracellular, but those that are secreted by cells and catalyse reactions outside cells are described as extracellular.

Question 39

Describe the active site of an enzyme.

Answer 39

Specific active sites that are complementary to the shape of the substrate. The substrate is held in place at the active site by weak hydrogen and ionic bonds. The combined structure is called the enzyme-substrate complex.

Question 40

What is activation energy?

Answer 40

Energy required in any chemical reaction to break the bonds in reactant molecules so that new bonds are formed to make the product. An enzyme lowers the activation energy required for the
reaction. However, the overall energy released during the reaction is maintained.

Question 41

Describe the lock-and-key theory.

Answer 41

The shape of the active site is exact
and substrates that are not complementary to the shape of the active site cannot bind. The enzyme-substrate complexes formed to enable the reaction to take place more easily.

Question 42

Describe the induced fit theory.

Answer 42

The enzyme’s active site is not an exact fit to the substrate molecule. However,
the enzyme molecules are more flexible and can change shape slightly as the substrate enters the enzyme. This
means that the enzyme molecule will undergo conformational changes as the substrate combines with the enzyme’s active site, forming the enzyme-substrate complex.

Question 43

Why do we measure the initial rate of reaction?

Answer 43

There are enough substrate molecules present to ensure that substrate concentration is not a limiting reactant
The substrate concentration is only known at the beginning of the reaction

Question 44

Describe nucleic acids.

Answer 44

Made up of Carbon, Hydrogen, Oxygen, Nitrogen, and Phosphorus
Monomers called nucleotides make up nucleic acids
They are made up of a pentose sugar, organic nitrogen base, and phosphoric acid
DNA molecules are double-stranded, RNA molecules are single-stranded

Question 45

What is a polynucleotide?

Answer 45

Many nucleotides are linked together
into a long chain-forming polynucleotides DNA/RNA.
Phosphodiester bonds formed by condensation reactions link the 5-carbon of one sugar molecule and the 3-carbon of the next. The polynucleotide strand is said to have 3’ and 5’ ends

Question 46

Describe the pentose sugars found in RNA and DNA.

Answer 46

Ribose (C5H10O5) present in RNA nucleotides

Deoxyribose (C5H10O4) present in DNA nucleotides

Question 47

Describe DNA.

Answer 47

Made up of two antiparallel polynucleotide strands lying side by side, held together by hydrogen bonds. These strands are arranged into a ladder-like structure called a double helix. The phosphate and the deoxyribose sugar form the backbone of the DNA molecule while the base pairs form the rings.

Question 48

What are the 4 nitrogenous bases present in DNA?

Answer 48

Adenine, thymine, guanine, and

cytosine.