SBI4U Midterm Review

What does cell theory state?

1.  All living things are composed of cells (or cell products)

2.  The cell is the smallest unit of life

3.  Cells only arise from pre-existing cells

What are some exceptions to cell theory?

Giant algae (not simple and large)

Striated muscle cells (large and multinucleated)

Aseptate fungal cells (share a cytoplasm and are large and multinucleated)

What are the five functions of membrane proteins?

Channels, carriers, recognition, receptors, and enzymes.

Recall: CCRRE

What do channel proteins do?

They have pores that act as channels that allow for passive transport of substances between the inside and outside of the cell.

What do carrier proteins do?

Proteins that bind to substances on one side of the membrane and use energy to change shape and transport them to the other side.

What do recognition proteins do?

Proteins that help the cell to diffrenciate between self and non-self cells.

What do receptor proteins do?

Proteins that span the whole membrane to relay information inside and outside of the cell.

What do enzyme proteins do?

Proteins that enhance the rate of reactions that occur at the membrane level.

Phospholipid structure

• Contain a polar (hydrophilic) head composed of phosphate (+ glycerol)

• Contain two non-polar (hydrophobic) tails, each composed of a fatty acid chain

• Amphipathic

What are the two properties of membranes?

• Semi-permeable (only certain things can cross)

• Selective (membranes can regulate material passage)

Amphipathic molecule

A molecule that has both a hydrophilic and a hydrophobic part.

Diffusion

The movement of particles from a region of high concentration to a region of low concentration, and is the result of the random motion of particles.

Osmosis

The passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration across a partially permeable membrane.

Hypertonic

High solute concentration, water goes out or the cell (osmotic loss of water).

Isotonic

Same salute concentration, no net movement of water.

Hyptonic

Low solute concentration, water goes into the cell (osmotic uptake of water).

Active transport

movement of molecules against concentration gradient, ATP is required (i.e. from low to high)

• Molecule binds to a transmembrane protein pump

• Hydrolysis of ATP causes a conformational change, translocating the molecule across the membrane

Passive transport

Movement of molecules along concentration gradient, no ATP expenditure

• simple diffusion

• facilitated diffusion

Simple diffusion

The net movement of particles from a region of higher concentration to a region of lower concentration (i.e. along the gradient) until equilibrium is reached

• Involves small / lipophilic molecules (e.g. O2, CO2, steroids)

Facilitated diffusion

The passive movement of molecules across a cell membrane via the aid of a membrane protein (carrier / channel protein)

• Involves large / charged molecules (e.g. ions, glucose, etc.)

• E.g. Voltage-gated channels control the flow of ions in neurons

Explain the importance of the surface area to volume ratio as a factor limiting cell size.

When the cell gets bigger its surface area to volume ratio gets smaller. If the surface area to volume ratio gets too small then substances won't be able to enter the cell fast enough to fuel the reactions and waste products will start to accumulate within the cell as they will be produced faster than they can be excreted. In addition, cells will not be able to lose heat fast enough and so may overheat. Therefore the surface area to volume ratio is very important for a cell as diffusion pathways should be kept short.

What are the monomers of DNA called?

Nucleotides

What are the two components of the DNA molecule?

Phosphate and pentose sugar.

What are the seven enzymes in DNA replication?

1. DNA gyrase

2. helicase

3. single stranded binding protein

4. DNA primase

5. DNA polymerase III

6. DNA polymerase I

7. DNA Ligase