Prokaryotes

Prokaryotic cells 

Prokaryotes include bacterium, these are smaller than eukaryote, and differ mainly as they have no nucleus or a nuclear envelope. Because of their small size (0.1-10 micrometres) this makes them very successful. Bacterium possess a cell wall which differs as it is made of murein rather than cellulose it is a polysaccharide combined with a polypeptide; murein doesn't stretch easily meaning that when osmosis occurs it resists activity. Bacterium further protect themselves by secreting a capsule of slime around its wall. 

Cell structure relating to its role: 

• CELL WALL- A physical barrier that excludes certain substances and protects against mechanical damage and osmotic lysis.
• CAPSULE- This protects bacterium from other cells and helps groups of bacteria stick together for further protection.
• CELL SURFACE MEMBRANE- Acts as a differentially permeable layer which controls entry and exit of chemicals.
• CIRCULAR DNA-This possess the genetic information for the replication of bacteria cells.  
• PLASMIDS- These posses the genetic information that may aid survival of bacteria in adverse conditions e.g. produces enzymes to breakdown antibiotics.
• RIBOSOMES- 70's (smaller than eukaryotes which are 80's) for protein synthesis
• FLAGELLUM- Used for locomotion.
• CYTOPLASM- Contains enzymes and soluble materials.  

Eukaryotes vs Prokaryotes 

Pro have no true nucleus just circular DNA within the cytoplasm wheres Eu have a distinct nucleus with a nuclear envelope. 

Pro DNA is not associated with proteins whereas in Eu histones are associated. 

DNA in Eu is linear and there are no plasmids whereas in Pro there are plasmids.

Only Eu contain membrane bound organelles e.g. mitochondria. 

Pro have smaller ribosomes (70's) compared to 80's of Eu.

cell wall made of meurin in Pro whereas cellulose in Eu, and Pro also contains capsule. 

Cell organelles

Eukaryotic cell structure

Eukaryotic cells differ from prokaryotic by the fact they have a distinct nucleus and posses membrane bound organelles. If we use a electron microscope with a short wavelength  , if has a high enough resolving power to see the complexity of our cells. Cells form the basic building blocks of life, and after the most recent scientific discovery scientists have concluded that their final cell count in humans is 37.2 trillions. Cells can duplicate themselves in processes called mitosis (which will be covered in a later post).

Mitochondria 

Have double membrane/ envelopeThey complete last stages of aerobic respiration and synthesise most ATP for the cellIs an energy generating organelleSurrounded by two membranes. Inner layer folds inwards to form the cristae. The cristae project into the liquid called the matrixThe inner membrane is coated in enzymes which catalyse the reactions of aerobic respiration to produce ATP.Abundant in cells with greater need for respiration (muscle and sperm etc.)Power houses of the cellCan be used in other metabolic processes such as synthesise of proteins.

Ribosome 

Made of proteins and ribosomal RNA

Translate instruction of messenger RNA into protein (makes proteins)

Can be attached to membrane (rough ER)

Can be floating freely in cytoplasm

Consist of one large and one small subunit

Lysosomes

Appear as darkly stained membrane bound structures

Known as ‘suicide bags’ as contain powerful hydrolytic enzymes (protease, lipases, carbohydrase’s and nucleases)

Enzymes kept separate from rest of cell

Role is to destroy damaged organelle and cells

Present in large number in the sperm head and white blood cells

Nucleus

Largest organelle

Surrounded by double membrane/ envelope

Outer membrane is continuous with RER

Pores are present which let mRNA and ribosomes out, nutrients and hormones in

Chromosomes are in loosely coiled stat known as chromatin

Nucleolus

Darker stained region within nucleus

Makes ribosomal RNA and packages it with ribosomal protein to make ribosomes

Darker heterochromatin is densely packed DNA

Lighter euchromatin is loosely pa ked DNA and acts as a template for mRNA synthesis

Cell wall

Gives support and structure in plat cells

Made from polysaccharide called cellulose

Can store carbohydrates

The cell wall doesn’t seal off from cell completely form its neighbours, there are pores within the walls called plasmodesmata. These connect two cells together by their cytoplasm, enabling exchange and transport of substances.

Cell membrane

Is very thin (7-10 nm)

At high magnification it seems o have a prelaminar- 3 layered

Appearance- 2 dark layers separated by pale middle layer

Selectively permeable controlling entry and exit of materials

Golgi body 

Series of tightly packed flattened sacs/cisternae

Collects and processes protein and lipid

It is made from vesicles budded form the ER which fuse at the forming face (nearest nucleus)

Vesicles bud off from the maturing face and go to either the surface membrane (secretion) or to form lysosomes

Chloroplasts 

Surrounded by double membrane/envelope

Flattened sacs or thylakoids run through internal solution or stroma

The sacs are stacked in places (called grana)

Site of photosynthesis. Grana trap light energy which is used to fix CO₂ in the stroma and build the sugar (glucose)

Cell vacuole

Permanent only exist in plant

Animals have temporary

Vacuole consists of membrane called tonoplast, filled with cell sap(watery solution of enzymes, sugars and pigments)

Important in keeping cell firm

When vacuole full of sap =turgid

Smooth ER

Lacks ribosomes

Makes lipids and steroids (cholesterol and sex hormones)

Contains enzymes that detoxify 

It is a storage site for calcium in skeletal muscle cells

Rough ER

Extensive membranous tubes are present within the cytoplasm. Much of it studied with ribosomes giving it rough appearance

Ribosomes makes protein which is transported within the ER’s flattened sac like sheets called cisternae.

Relating cell organelles to their functions 

Some organelles are present in large amount in specific cells for example muscle cells contain many mitochondria: this is due to the frequent amount of activity muscle cells carry out which requires them to constantly aerobically respiring which is carried out in the mitochondria. 

A epithelial cell which lines the wall of the wall of the small intestine will have many carrier proteins present which results in the need for  excessive rough ER this is so that the ribosomes can constantly translate the mRNA for making polypeptides to produce the proteins to carry out active transport, facilitates diffusion and co transport for the absorption of glucose. 

Diffusion 

It is important to understand that:

• All particles are constantly in motion due to kinetic energy that they possess
• Motion is random, no set pattern
• Particles are constantly bouncing of one another and off other objects
• Particles will distribute themselves equally as a result of diffusion
• Only non polar molecules can diffuse straight through the membrane surface such as oxygen

Simple Diffusion:
passive as energy comes rom an inbuilt motion of particles (natural)  

THE NET MOVEMENT OF PARTICLES/IONS FROM A REGION WHERE THEY ARE MORE HIGHLY CONCENTRATED TO ONE WHERE THEIR CONCENTRATION IS LOWER UNTIL EVENLY DISTRIBUTED

Facilitated Diffusion

The movement of molecules such as charged ions and polar molecules do not diffuse easier due to their hydrophobic nature of the fatty acids tails in the phospholipid membrane, so transmembrane channels and carriers span the membrane (facilitated diffusion).
This occurs when a molecule isn't lipid soluble, polar, charged or is too big

Similar to simple diffusion as:

• Passive process relies on inbuilt kinetic energy of diffusing  molecules
• Occurs down a conc gradient

But differs as:

• Only occurs at specific points on the membrane where protein channels and carrier proteins are present

Carrier proteins

When a molecule is specific (complementary) to the molecule present the bind. This causes the protein to change shape in a way that the molecule is released inside the cell membrane. 

This uses the kinetic energy of the particles itself

It occurs down a concentration gradient where the solute concentration inside the cell membrane must be lower than outside for it to diffuse in. 

Channel protein 

These form water filled hydrophobic channels across the cell membrane. These allow water soluble ions to pass through. Channels will only open to specific molecules and so if the specific ion isn't present it will remain closed. Ions binds to proteins causing it to change shape in a way that closes it on one side and opens up one another.