the cell lecture packet 4 reading: chapter 3 (pages 43-56) copyright 2008 pearson education

COPYRIGHT 2008 PEARSON EDUCATION

The CellLECTURE PACKET 4

READING: CHAPTER 3 (PAGES 43-56)


Outline

▪ Eukaryotic cells vs prokaryotic cells▪ Cell size and microscopy▪ Cell structure and function▪ Plasma membrane▪ Organelles▪ Cytoskeleton


Cells

▪ Cells are the basic unit of life. ▪ Cells are highly structured. ▪ They are enclosed in a membrane—the plasma membrane.▪ Cells vary in size but there is a limit on how big a cell can be and survive.▪ There are different types of cells—specialized cells.


Cells

▪ Some organisms (like yeast) are just one cell.


Cells

▪ Multi-celled organisms have specialized cells.


Prokaryotes

▪ Prokaryotic cells are structurally simpler than eukaryotic cells.

▪ They are limited to bacteria and archaea (species dwelling in hot sulfur springs or high-saline lakes).

▪ Most prokaryotic cells are surrounded by a rigid cell wall.


Prokaryotic vs eukaryotic cells review


Which are examples of prokaryotic organisms?

1. Animals2. Plants3. Bacteria4. Fungus


Prokaryotic cells have a nucleus.

1. True2. False


Cell size

▪ Cells vary in size, but they can never exceed the volume that can be nourished by materials passing through the surface membrane. ▪ Volume grows faster than surface area, so the ratio gets smaller.▪ A larger ratio is better for cells better diffusion rates.


Major features of a cell


Plasma membrane

▪ The plasma membrane is a thin membrane that controls the movement of substances both into and out of the cell.

▪ Fluid mosaic model- Molecules are free to move around- Mixture of phospholipids, steroids (cholesterol), and proteins

▪ Selectively permeable- Some things can cross freely, while others need to help being transported over


Plasma membrane

▪ It is considered a phospholipid bilayer.- Phospholipids arrange to have the polar head on the outside and the non-polar, fatty acid tail on the inside. - Proteins and sterols (cholesterol) are arranged on surfaces

and can form channels.


Plasma membrane functions


Five main components in plasma membrane

1. Phospholipid bilayer- Phosphate head (hydrophilic)- Fatty acid tails (hydrophobic)- Controls what passes through membrane

2. Cholesterol- Mains fluidity of membrane



3. Proteins- Transport, support, communication, recognition

4. Glycoproteins- Chains of sugars attached to a protein- Functions: attachment sites, cell recognition

5. Glycolipids- Chains of sugars attached to a lipid- Functions: attachment sites, cell recognition


Movement across membrane

▪ The plasma membrane divides the inside of the cell from the outside environment (interstitial fluid).▪ It is semi-permeable: not everything can freely pass through it.

▪ Molecules typically go from an area of high concentration to an area of lower concentration, unless energy is provided.

▪ If you add molecules to water, it will disperse (diffuse) until it is equally distributed in the water.


What can freely cross the plasma membrane?

1. Gases: oxygen, carbon dioxide, etc.

2. Hydrophobic compounds (non-polar).

3. Very small uncharged molecules (water). Even though water is polar, it is small and somewhat permeable.


What cannot freely cross the plasma membrane?

1. Ions (charged elements)

2. Hydrophilic (polar compounds) larger than water.

3. Charged molecules in general

4. Macromolecule compounds (i.e., large proteins, complex carbohydrates, triglycerides)


Osmosis: movement of water

▪ Osmosis is a type of diffusion in which water moves across a plasma membrane or any other selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.


Osmosis

▪ Hypertonic: Concentration of solutes is higher on the outside relative to the inside.

▪ Isotonic: Inside and outside have the same concentration.

▪ Hypertonic: Concentration of solutes is lower outside than inside.


Osmosis


Transport of other molecules

▪ Passive transport- Does not require energy, and uses a concentration gradient- There is simple diffusion (no carrier molecule)- There is facilitated diffusion (with carrier molecule)

▪ Active transport- Does require energy- Goes against a concentration gradient


Transport: simple diffusion

▪ Net diffusion: molecules that can freely pass through the membrane are controlled by the concentration gradient (more molecules will move from higher concentration to lower concentration than from lower concentration to higher concentration).

- Gases can cross freely- Very small molecules that are not charges (such as water)- Hydrophobic (non-polar) molecules- Remember: does not require energy


Transport: simple diffusion


Transport: facilitated diffusion

▪ Facilitated diffusion: aided by a carrier protein, and controlled by a concentration gradient

- Hydrophilic molecules like glucose and amino acids- Polar molecules - Remember: does not require energy


Transport: facilitated diffusion


Transport: active transport

▪ Active transport is a mechanism that moves substances across plasma membranes with the aid of a carrier protein and energy supplied by the cell (through the breakdown of ATP).

▪ Typically, movement is from a region of lower concentration to a higher concentration.

- The cell will use energy to help this movement.


Transport: active transport


Transport: summary


Can calcium (Ca2+) pass freely through the membrane?

1. Yes2. No


Can glucose pass freely through the membrane?

1. Yes2. No


Simple diffusion requires the input of energy

1. True2. False


Transport using a vesicle

▪ When the cell needs to transport larger things (i.e. macromolecules, bacteria, fluids) they can use vesicles to transport things in and out of the cell.

- Exocytosis: moving things out of the cell using a vesicle.- Endocytosis: moving things into the cell using a vesicle.


Transport: endocytosis

▪ There are a few types of endocytosis- Phagocytosis: when cells transport large particles and cells

(bacteria) into the cell using vesicles- Pinocytosis: when cells transport fluid into the cell using

vesicles.- Receptor-mediated endocytosis: when membrane receptors

are involved.


Transport: endocytosis - phagocytosis


Transport: endocytosis - pinocytosis


Transport: receptor-mediated endocytosis

▪ An example is cholesterol


Transport: exocytosis


Transport: review


Major features of eukaryotic cells


Cell: nucleus

▪ The cell nucleus contains almost all of the cell’s genetic information (DNA).

- This DNA is used to build proteins.- The genetic information is organized into chromosomes, or

DNA associated with proteins.- The number of chromosomes differ from one species to

another.- Humans have 46 chromosomes- Mice have 40 chromosomes- Dogs have 78 chromosomes


Cell: nucleus


Cell: nucleus

1. Nuclear envelope: double membrane (two different bilayers)- Inside layer contains sites for DNA to attach- Outside surface layer has many ribosome

2. Nucleolus: dense are in the nucleus where ribosomes are synthesized.

3. Nucleoplasm: area inside the nucleus4. Chromatin: DNA and its associated proteins


Cell: nucleus


Cell: ribosomes

▪ Function: site of protein synthesis

- This is where amino acids are linked together with a peptide bond to make a polypeptide chain.▪ Ribosomes are composed of proteins and ribosomal RNA (rRNA).


Cell: endoplasmic reticulum

▪ There are two types of endoplasmic reticulum- Rough endoplasmic reticulum- Smooth endoplasmic reticulum


Cell: endoplasmic reticulum


Cell: rough endoplasmic reticulum

▪ Endoplasmic reticulum that has ribosomes associated with it is called rough endoplasmic reticulum.

▪ Rough endoplasmic reticulum makes proteins that will be incorporated into membranes or secreted by the cell.


Cell: rough endoplasmic reticulum

▪ Function: important for protein modification.

▪ Here, polypeptide chains are folded into their shape by chaperones.

▪ Also here, carbohydrate tags are added to the proteins (glycosylation).

- Proper folding- Stabilize proteins- Cell-cell adhesion


Cell: smooth endoplasmic reticulum

▪ Endoplasmic reticulum that does not have ribosomes associated with it is called smooth endoplasmic reticulum.

▪ Phospholipids and steroids are synthesized here.

▪ It contains enzymes that detoxify alcohol and some drugs.

▪ These phospholipids, along with proteins from the RER, are used to make the RER membrane.

- Because the RER membrane is used continually to form vesicles for shipping, it must be replenished.


Cell: golgi complex

▪ The golgi complex is a series of flattened membranous sacs.

▪ Vesicles from rough and smooth endoplasmic reticulum bring their products to the golgi to be modified and repackaged.

▪ Golgi apparatus chemically modifies many proteins as they move from one membrane to another.

▪ It processes, sorts, and packages proteins and lipids.


Cell: golgi complex


Cell: lysosomes

▪ Lysosomes are digestion vesicles that contain strong acids and digestive enzymes (about 40 different ones). It can fuse with plasma membrane to expel waste.

▪ The enzymes and membranes of lysosomes are made by the RER and then sent to the Golgi complex for additional processing.

▪ Functions:- Lysosomes break down obsolete parts of the cell.- Destroy bacteria.- Engulf molecules and digest them.


Cell: lysosomes


Tay-Sachs disease

▪ Tay-Sachs is a hereditary disease where people don’t have an enzyme normally found in lysosomes that breaks down lipids in nerve cells.

- Accumulation of lipids in the nervous system, thereby causing paralysis and death.


Cell: mitochondria

▪ All eukaryotic cells contain mitochondria.

▪ It is bounded by a double membrane. - Outer membrane faces cytoplasm. - Inner membrane folded. This folded, called cristae,

increases the surface area available for cellular respiration.

▪ Mitochondria produce energy for the cell (ATP). This process requires oxygen.

▪ They are also important in apoptosis (programmed cell death).


Cell: mitochondria


Where are polypeptide chains/proteins produced?

1. Nucleus2. Ribosomes3. Golgi complex4. Smooth endoplasmic reticulum


Where are polypeptide chains/proteins folded?

1. Nucleus2. Ribosomes3. Golgi complex4. Rough endoplasmic reticulum


What organelle produces energy for the cell?

1. Nucleus2. Ribosomes3. Mitochondria4. Rough endoplasmic reticulum


Cytoskeleton

▪ Interconnected system of fibers and lattices between the nucleus and the plasma. Microtubules are straight, hollow rods made of the protein tubulin.

▪ Functions:- Gives cells their organization (location of things)- Shape- Ability to move- Transport things in cell- Aid in cell division


Cytoskeleton

▪ Three major types of cytoskeleton- Microfilaments- Microtubules - Intermediate filaments

▪ Intermediate filaments tend to be permanents▪ Microtubules and microfilaments reassemble and disassemble often.


Cytoskeleton: microtubules

1. Microtubules serve as tracks along which organelles or vesicles move.

2. They maintain cell shape. 3. They play a role in the separation of chromosomes during cell

division. 4. They are also responsible for the structure and movement of

cilia and flagella. - Cilia are numerous short extensions in a cell that move back

and forth.- Flagella are larger than cilia and move in an undulating

manner.


Cytoskeleton: microtubules


Cytoskeleton: microfilaments

▪ Microfilaments are solid rods made of the protein actin.

▪ Functions:- Important function in muscle contraction.- Role in dividing cells during cell division.


Cytoskeleton: intermediate filaments

▪ They are a diverse group of ropelike fibers helping to maintain cell shape and anchoring certain organelles in place. Their protein composition varies.

the cell lecture packet 4 reading: chapter 3 (pages 43-56) copyright 2008 pearson education

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