B.1.1 Flashcards
(12 cards)
Role of glycoproteins in cell-to-cell recognition
On the plasma membrane of the red blood cell there are glycoproteins with specific antigens attached to the carbohydrate chain. These antigens are used for cell-to-cell recognition, this is because depending on the specific antigen attached to the glycoprotein is will define one certain type of blood or another. In apes for example, if the red blood cell has glycoprotein + galactose it is type B, if it has glycoprotein + acetyl galactosamine it is type A, if it has both it is type AB, and lastly if it has none it is type O. The way this works is that the immune system uses these antigens to identify the body’s own cells and stop itself from attacking them.
When someone with type A blood gets a blood transfusion it needs to be either type A blood or type O blood because red blood cells with type A blood have type B antibodies and if there is type B antigens in a type A person’s body their immune system will attack them and viceversa, type O though works for both type A and B because it has to antigens but it cannot receive blood from either (only other type O) because it has both type A and B antibodies. The opposite is true for the AB type, it can receive blood from both A and B because it has both antigens but due to having both neither type B nor type A can use it because it will activate the antibodies. This is why type AB is called the universal recipient and why type O is called the universal donor
Steroids
Steroids are a group of lipids that form naturally occurring hormones to carry out different physiological functions in the body. Their structure is composed of four carbon-based rings with differences in the functional groups depending on the hormone. Non-polar steroid, being hydrophobic, can freely diffuse through the plasma membrane.
A steroid found in the membrane is cholesterol, it provides structure and flexibility to the plasma membrane of the cells.
Condensation reaction & hydrolysis
Condensation reactions are when two different molecules join together to form a larger more complex molecule by joining areas that together can form the molecule H2O (water molecule), so once these parts are formed the molecules are joined and an H2O molecule is formed as a product of the reaction.
Hydrolysis is the opposite, it is using H2O to break down molecules.
Cellulose
Like starch and glycogen it is also composed of glucose but in this case, cellulose is composed of beta glucose instead of alpha. Therefore even though it also uses 1-4 glycosidic bonds these do not form a helical structure as the structure of beta glucose allows them to be in a straight chain. Unlike starch and glycogen though, cellulose is used for structure not energy storage, cellulose is what mainly composes the cell wall for example.
Carbon
Carbon is an element found in all organic molecules, therefore without carbon, life cannot exist. It can form 4 covalent bonds and can appear in different shapes like tetrahedral, ring shapes (pentose, hexose etc.), and can form chains that are branched or unbranched.
Phospholipids
Phospholipids are molecules composed of 2 fatty acid tails (hydrocarbon tails) and a phosphate group, these being connected by a glycerol molecules. The structure is the same as triglycerides except for instead of 3 fatty tails one of them is replaced by the phosphate group. Since the phosphate head is hydrophilic and the hydrocarbon tails are hydrophobic the molecule is amphipathic. Due to those amphipathic properties, in aqueous environments phospholipids form a bilayer as the hydrophilic regions are attracted to the water while the hydrophobic regions are attracted to other hydrophobic phospholipid regions. This is how the plasma membrane is formed.
Saturated and unsaturated fatty acids
The fatty acid chains in triglycerides are formed with one carbon bonding to 2 carbons on its sides and bonding with hydrogen one on top and one below. For these chains to be saturated, it means that there are no double bonds between the carbons. Saturated fatty acids are usually seen in fatty animal products such as butter and due to their compactness they have a lower melting point and therefore appear as solid at room temperature. They have high coronary heart disease impact.
Unsaturated fatty acids on the other hand are when there IS a double bond between two carbons, this leads to both of the carbons not bonding with 2 hydrogens and instead bonding with only 1 hydrogen.
In cis unsaturated fatty acids this makes the chain bend because due to the bond with only one hydrogen for two connected carbons it creates a gap below or above being the chain bend. The bending of the chain separates it from other chains creating more fluidity which allows these fatty acids to have a higher melting point and to appear as liquid in room temperature. They have low coronary heart disease impact.
On the other hand trans unsaturated fatty acids still have the double bond but one hydrogen is on top while the other is on the bottom balancing out the chain so it does not bend. These types of unsaturated fatty acids are artificial and have a lower melting point appearing as solid in room temperature, for example margarine. They have very high coronary heart disease impact.
Starch
Starch is used for energy storage in plants and is divided into 2 different parts, amylose 20% of starch or amylopectin which is 80% of starch.
Amylose is a chain of alpha glucose with 1-4 glycosidic bonds forming a helix-like structure with no branching.
Amylopectin on the other hand is also a chain of alpha glucose with 1-4 glycosidic bonds but it does have branching with 1-6 glycosidic bonds forming a more spherical shape, the 1-6 bonds happen in 1 in 20 glucose molecules.
When energy is needed a hydrolysis reaction breaks down a 1-4 glycosidic bond to take the glucose and transport it to wherever needs energy.
Glycogen
Glycogen is the energy storage in animals. It has a similar structure to amylopectin with a 1-4 glycosidic bond chain of alpha glucose and 1-6 glycosidic bond branching but in glycogen the 1-6 branching is in 1-10 glucose molecules instead of the 1-20 amylopectin distribution.
When energy is needed a hydrolysis reaction breaks down a 1-4 glycosidic bond to take the glucose and transport it to wherever needs energy.
Glucose isomers and types of sugars
An isomer is a molecule that has has the same chemical composition but with different structure. Glucose isomers include alpha and beta glucose, fructose, and galactose.
Glucose is a monosaccharide that stores energy and is easily absorbed.
Fructose is a monosaccharide that stores energy in plants
Galactose is a monosaccharide that stores energy
Sucrose is a disaccharide between glucose and fructose and is a soluble energy storage for plants
Lactose is a disaccharide between glucose and galactose and is energy store found in milk
Maltose is a disaccharide between glucose and glucose and is an energy store found in seeds.
Fats as energy storage and thermal insulation
Triglycerides are great for long term energy storage due to many factos such as:
- They are chemically stable, so energy is not lost over time
- They have little to no solubility in water so they have no osmatic effects on the cell (unlike glucose)
- They release twice as much energy per gram in cell respiration compared to carbohydrates
- So enough energy can be stored in less body mass which is good for animals that move a lot like birds
- They are poor conductors of heat so they can be used as thermal insulators to conserve body heat
- They are liquid at body temperature so they can be used as shock absorbers
Glucose form and function
Glucose is a carbon based molecule with a hexose ring structure of C6H12O6. It is a small monosaccharide molecule and due to its size it can be easily transported, this factor and also it being soluble lead to it being transported around the body through the blood, dissolved in the plasma. As well as molecular size glucose is chemically very stable which is why it is great for food storage, although because large amounts of glucose in cells cause osmatic problems glucose is usually turned into either glycogen in animals or starch in plants. Lastly, glucose yields energy when it is oxidized so it is a good substrate for respiration.
