Chapter 3 ANP

Question 1

Explain how the chemical properties of phospholipids contributes to the structure and
permeability of the phospholipid bilayer.

Answer 1

75% of the lipid bilayer is phospholipids (glycerol joined by to two fatty acids and a phosphate group)

The hydrocarbon chains of the fatty acids act as nonpolar, hydrophobic tails while the rest of the molecule acts as a polar, hydrophilic head. Phospholipids form bilayers that function as biological membranes.

Phospholipids have 2 ends,the head which is hydrophilic (loves water) and the tail composed of lipids which is hydrophobic (hates water) so phospholipids come together in way where the heads are pointed outside and the tails inside to avoid the contact of the tails with water.Thus forming the bilayer

Question 2

Compare & contrast simple diffusion, facilitated diffusion, osmosis, and active transport.

Answer 2

Diffusion
One method of movement through the membrane is diffusion. Diffusion is the movement of molecules from a region of higher concentration to one of lower concentration. This movement occurs because the molecules are constantly colliding with one another. The net movement of the molecules is away from the region of high concentration to the region of low concentration.

Diffusion is a random movement of molecules down the pathway called the concentration gradient. Molecules are said to move down the concentration gradient because they move from a region of higher concentration to a region of lower concentration. A drop of dye placed in a beaker of water illustrates diffusion as the dye molecules spread out and color the water.

Osmosis
Another method of movement across the membrane is osmosis. Osmosis is the movement of water from a region of higher concentration to one of lower concentration. Osmosis often occurs across a membrane that is semipermeable. A semipermeable membrane lets only certain molecules pass through while keeping other molecules out. Osmosis is really a type of diffusion involving only water molecules.

Facilitated diffusion
A third mechanism for movement across the plasma membrane is facilitated diffusion. Certain proteins in the membrane assist facilitated diffusion by permitting only certain molecules to pass across the membrane. The proteins encourage movement in the direction that diffusion would normally take place, from a region with a higher concentration of molecules to a region of lower concentration.

Active transport
is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellular energy to achieve this movement.

Question 3

Describe the various roles of proteins in the phospholipid bilayer.

Answer 3

• Integral proteins
  – Most are transmembrane proteins (span membrane) – Function as transport proteins (channels and carriers),
  enzymes, or receptors
• Peripheral proteins
• peripheral proteins are only on the one side of the lipid bilayer, either the outside of the cell or the cytoplasmic side inside the cell, but not both.
  – Loosely attached to integral proteins – Include filaments on intracellular surface used for
  plasma membrane support – Function as:  Enzymes
   Motor proteins for shape change during cell division
  and muscle contraction
   Cell-to-cell connections

Question 4

Describe the role of carbohydrates in the plasma membrane.

Answer 4

ID the molecules
Allow cells to ID during development to become tissue s and organs
Immune sys to ID foe v friend
Only outer
glycocalyx

Question 5

Explain how cholesterol contributes to the structure of the plasma membrane.

Answer 5

stiffens membrane
Further decreases water solubility of membrane
Typical 4 ring steroid structure

Question 6

Explain what happens in each of the three sub-phases of interphase

Answer 6

G1 phase, S phase, G2 phase. The newly formed cell matures during the G1 phase. If the cell is going to divide, it enters the S (synthesis) phase where the DNA is replicated and the G2 phase where more growth occurs.

Question 7

Explain the function of the enzymes involved in protein synthesis.

Answer 7

The enzyme’s activity is to form peptide bonds between adjacent amino acids using tRNAs during translation.
involves the linking together of amino acids in correct sequence

Question 8

Explain what Okasaki fragments are & why they form during DNA replication.

Answer 8

short sections of DNA formed at the time of discontinuous synthesis of the lagging strand during replication of DNA

They are formed in the lagging strand by the initiation of the creation of a new RNA primer by primo some.