Cell Structure and Function

Ok, now you should have done this in Grade 8 and 9 science, but we are going to review our cell biology! Let’s get to it!

1. Cell Levels Of Organization The Cell marks our basic boundary between living and non living things. If you are made up of one or more cells you are living. If not, you are out of luck! Cells can be classified into two different categories: Prokaryotic: lacks membrane bound structures (No nucleus) Bacteria Eukaryotic: Has membrane bound organelles Animal or plant cells

• English scientist Robert Hooke in 1665 first described cells from his observations of cork slices. Hooke first used the word "cell".

• Dutch amateur scientist Antonie van Leeuwenhoek discovered microscopic animals in water

• German scientists Schleiden and Schwann in 1830's were first to say that all organisms are made of one or more cells.

• German biologist Virchow in 1858 stated that all cells come from the division of pre-existing cells.

• Cells are the building blocks of life. (Raycroft- 2000) 2. Cell Theory: Cell theory states the following 1. All organisms are composed of one or more cells 2. Cells are the basic unit of all life 3. All cells come from pre-existing cells.

3. Cell Size: Cells are small. Why? Why are we not made up of larger cells? Isn’t bigger better?

Cells are small because: 1. If one ‘breaks’ in a multicellular organism, it

can be replaced without a large amount of energy being consumed

2. Diffusion of nutrients and wastes in a smaller cell is easier than in a larger cell

3. As a cell gets larger it’s surface area to volume ratio gets smaller, this makes it inefficient

4. Prokaryotic Cells Eukaryotic Cells evolved from Prokaryotic cells.

Bacteria can be classified into Archaea (no peptidoglycan in cell wall) and Bacteria (has peptidoglycan) The Process of Evolution from Prokaryote to Eukaryote is known as Endosymbiotic Theory.

5. Basic Eukaryotic Cell Anatomy Structure Composition Function Cell Wall * Contains Cellulose and Fibrils Support and Protection of plant cells Plasma Membrane

Phospholipids Bilayer with embedded proteins for pore transport

Defines cell boundary; regulates molecules passage into and out of the cell

Nucleus Nuclear Envelope Nucleoplasm chromatin and nucleoli

Storage of DNA for protein synthesis

Nucleolus Concentrated area of chromatin, RNA and Proteins

Where RNA is told where to go for Subunit formation

Ribosome

Protein and RNA in two Subunits (non identical

Protein Synthesis

Endoplasmic Reticulum Membranous flattened channels and tubular canals

Synthesis and or modification of proteins and other substances distributed by vesicles formation Cell’s membrane factory- Phospholipids and Cholesterol

Rough ER Have Ribosomes Folding, Modification, and transport of proteins

Smooth ER No Ribosomes Various, lipid synthesis in some cells Can Detoxyfy some substances

Golgi Apparatus (Body)

Stack of Membranous saccuoles

Processing, packaging, and distribution of proteins and lipids (Mail ROOM)

Lysosome ** (Animal) Membranous vesicle containing digestive enzymes

Intracellular Digestion

Vacuole and Vesicle Membranous Sacs Storage of substances Peroxisome Membranous vesicle

containing specific enzymes The Enzymes in peroxisomes break down molecules and as a result produce hydrogen peroxide molecules

Mitochondrion Inner Membrane (Cristae) bound by outer membrade

Cellular Respiration

Chloroplast * (Plants) Membranous grana bound by

2 outter membranes Photosynthesis

Cytoskeleton Microtubules intermediate

filiaments actin filaments Shape of the cell and the movements of its parts

Cillia and Flagella 9 +2 pattern of microtubules Movement Centriole ** (Animals)

9 + 0 pattern of microtubules

Cell division

6. Nucleic Structures: Chromatin: DNA and Protein Structures Nucleolus: Chromatin and Ribosomal subunits Nuclear Envelope: Double membrane with pores. 7. The Endomembrane System How do things get into and out of the cell? Part of that is vesicles that are incoming and secretory, which gets things into and out of the cell.

The Plasma Membrane: A Closer Look The Plasma membrane is a phospholipids bilayer which separates the inside of the cell from the outside of the cell. It is the gate keeper for the ins and outs of all molecules entering or exiting the cell.

1. Structure and Function a. It contains a variety or mosaic of biological molecules, primarily proteins and lipids, which are involved in a vast array of cellular processes, and also serves as the attachment point for both the intracellular cytoskeleton and, if present, the cell wall. The membrane is not solid but fluid , with shifting phospholipids and

proteins. This is called the FLUID MOSAIC MODEL of the membrane

b. Phospholipids Phospholipids contain glycerol, two fatty acids, and a phosphate group.

The phosphate group is polar (hydrophilic), enabling it to interact with water. The fatty acid tails are nonpolar (hydrophobic) and do not interact with water. The Polarity of the bilayer has the polar heads interacting together and the nonpolar tails interacting together. So that the non polar tails don’t interact with water.

2. Function of Proteins

a. Channel Proteins Passage of molecules through the membrane. Is specific to certain molecules. Ex- Hydrogen Ion flowing across mitochondrial membrane to make ATP b. Carrier Proteins Combine with a substance to help it move across the membrane. Ex- sodium and potassium ions in the nerve cell membrane.

c. Cell recognition proteins MHC (major histocompatibility complex) glycoproteins that act as flags on the outside of the cell. Cells with foreign glycoproteins are attacked by which blood cells. d. Receptor Proteins Shaped in such a way that specific molecule can bind to it. e. Enzymatic Protein Catalyzes a specific reaction (Speeds up but is not USED up) 3. Diffusion, Osmosis and Tonicity

a. Diffusion Movement of particles from high concentration to low concentration

b. Osmosis Movement of water molecules from high concentration to low concentration àthe more dissolved particles in solution, the greater the tendency of water to move into it and the higher the osmotic pressure

Make sure you read questions carefully because the yellow particles are not permeable to this membrane. The blue ones are!

c. Tonicity

Tonicity is the concentration of a solute (dissolved substance in liquid) on either side of a membrane

Hypotonic Solution= More water on the outside of the cell Isotonic Solution = Equal parts of water on inside and outside Hypertonic Solution = More water in the inside of the cell (IE more solvent in solution) What should a cell do in each of the situations?

Hypotonic

Isotonic

Hypertonic

Osmolarity is a measure of the osmotic pressure exerted by a solution across a perfect semi-permeable membrane (one which allows free passage of water and completely prevents movement of solute) compared to pure water.

Tonicity of Solution Cell is Put Into

Net Movement of Water

Effect on Cell

Isotonic

No net movement

Remains the same

Hypotonic

Cell gains water

Cell Swells & May Burst

“lysis”

Hypertonic

Cell loses water

Cell Shrinks

“crenation”

Isotonic ("same" "strength") solution: no net movement of water across membrane. Same number of solute molecules per unit volume Cells placed in such a solution neither gain or lose water a 0.9 percent solution of NaCl is isotonic to red blood cells (RBC). How can you tell this is so?

Hypertonic Solutions ("greater" "strength") greater concentration (symbol for concentration ="[ ]") of solute than the cell (and therefore a lesser [ ] of water if a cell is placed in hypertonic solution, water will leave the cell and the cell will shrivel up. This is called crenation in animal cells. e.g. a 10% solution of NaCl is hypertonic to RBC -- they'll shrink Hypotonic Solutions ("hypo" means "less than") these solutions have lower concentration of solute than the cell contents. if cell placed in hypotonic solution, water will enter cell, it will swell and possibly burst. e.g. a salt solution with a concentration greater than 0.9% is hypotonic to RBC.

Tonicity of Solution Cell is Put Into

Net Movement of Water Effect on Cell

Isotonic

No net movement

Remains the same

Hypotonic

Cell gains water

Greater water pressure inside cell

“turgor pressure”

Hypertonic

Cell loses water

Cell Contents Shrink, but cell wall retains its shape

“plasmolysis”

Hypertonic solutions cause plasmolysis (shrinking of cell due to osmosis). central vacuole loses water, cell membrane shrinks and pulls away from cell wall. Hypotonic solutions causes turgor pressure, against rigid cell wall (turgor pressure occurs when plant cells, placed in hypotonic solution, admit water. As water enters, pressure builds up inside the cell (hydrostatic pressure). When hydrostatic pressure = osmotic pressure, the plant is said to have developed turgor pressure). cell wall keeps cell from bursting osmosis continues until turgor pressure = osmotic pressure turgor pressure important for plant cells to retain erect positions. Now you should be able to explain why plants wilt when you don’t water them!

4. Selectively Permeable Movement Some particles can pass freely through the membrane, while others cannot. The membrane can control how much of each substance comes into or out sometimes. Nonpolar Molecules pass through more easily than polar. That is because of the nonpolar tails of the phospholipids. Small Polar molecules pass through protein channels(Water)

Name Examples

1. diffusion lipid-soluble molecules, water, gases 2. transport by carriers (active and facilitated transport)

sugars and amino acids sugars, amino acids., ions

3. endocytosis and exocytosis (e.g. pinocytosis and phagocytosis)

macromolecules (e.g. proteins), cells or subcellular material

a. Porins (Passive Diffusion) These protein channels have a nonpolar outside and a polar inside so they can span the entire plasma membrane. They allow for passive diffusion of some particles. à Porins are composed of 2nd degree beta sheet proteins

à salts, ions, glucose and larger polar molecules cannot pass through these protein porins

b. Facilitated Transport/ Diffusion

This is the passage of molecules through specific channels. This means they are specific to the type of molecule they are letting through them. The molecules are passed through Specific Channels or Carrier Molecules

à This process does not require any energy because it uses concentration gradients and the process of diffusion

c. Active Transport

When a molecule still needs to pass through the membrane, but is on the side of lower concentration it will take “active transport” to get it across the membrane.

à they pass through carrier proteins à This process requires energy

à proteins which are involved in active transport are often called pumps because they force something against osmosis or diffusion. à one of the most important pumps of this type is called a sodium-postassium pump. It is associated with nerve and muscle cells.

5. Endocytosis and Exocytosis: another way to get molecules, especially large particles, in and out of cell.

Endocytosis: cell membrane forms a vesicle around the substance to be taken in.

a. Phagocytosis: what you call endocytosis if particles taken in really large (like other cells - e.g. human macrophages). Can be see with light microscope.

b. Pinocytosis: (= cell drinking) - same idea as phagocytosis, except smaller particles taken in (requires electron microscope to see).

Exocytosis: Reverse of endocytosis. Vacuole within cell fuses with cell membrane and the vacuole contents are deposited on the outside. Important in secretion and excretion in cells.