Study notes unit 2

Protein Synthesis

Protein synthesis occurs in both the ribosomes and the nucleus. Step 1 the DNA unwinds and unzips because the mRNA needs it to make a copy. The DNA is like a template that RNA uses. This is the process known as transcription. The DNA code determines the order of the mRNA nucleotides. The mRNA copies the DNA. mRNA then leaves the nucleus and heads towards a ribosome, where translation is about to occur. In translation the mRNA attaches to the ribosome and the tRNA brings the amino acids. The amino acids bond together to begin making the new protein. The ribosome can only hold two tRNA at a time. The mRNA dictates which tRNA and amino acids arrive at the ribosome. Thousands of amino acids bond together to form a chain, which is the new protein. When the protein is constructed the mRNA releases the the stop codon and then the protein is released from the ribosome

The information in the mRNA base sequence is in a triplet code. Each three letter unit of the molecule is called a codon. So a specific sequence produces a specific amino acids

Two examples of environmental mutagens that can cause mutation in humans are Ultraviolet radiation and X rays.

In the mutation due to X-Rays, it can break the backbone of the DNA molecule. Special enzymes will repair the break but the spliced segment may not be returned to the right position. The misplaced segment can alter all of the genetic information.

Transport Across Cell Membrane

Glycolipid- consists of a carbohydrate chain and a lipid. They provide the cell with a self recognition marker.
Glycoprotein (or recognition protein)- consists of a carbohydrate chain and a protein. Serve as cell surface attachment sites.
Phospholipids- main structural component of the membrane, isolates the cell's cytoplasm from the exterior.
Cholesterol- lipid found embedded within the plasma membrane, makes the bilayer stronger and more flexible, makes the membrane less permeable.
Carbohydrate- may attach to parts of the membrane (forming glycolipids or glycoproteins) and can act as receptor sites.
Receptor Protein- molecular triggers that set off cellular responses when specific molecules in the extracellular fluid bind to them (have a binding site).
The cell membrane is described as "selectively permeable" because the membrane can choose what it allows to enter and exit the cell. For example the membrane can choose to allow water but not chemicals into the cell.
Diffusion and osmosis are passive. This means that they do not require any energy input. Diffusion is the movement of a substance from an area of high concentration to an area of low concentration.An example of diffusion is putting sugar into a cup of water. The sugar will disolve slowly into the water.
Osmosis involves the movement of water. In osmosis, water is the only thing that moves. Osmosis requires a membrane that is semi-permeable so it can enter or exit a cell. Facilitated transport is also passive, in which material are moved across the plasma membrane by a transport protein from high concentration to low concentration. But it does not require energy. Active transport is the movement of a substance up a concentration gradient through a selectively permeable membrane us ATP, which is energy. Which means in active transport it moves something from low concentration to high concentration
Size: Small molecules can slip by the polar heads of the phospholipids and through the membrane to the other side. Oxygen gas, carbon diozide and water can move in this manner. Very large molecules like protein cannnot diffuse across the cell membrane
Surface area: The more surface area a cell has, it's ability to absorb what it needs and wants increases. So that the rate of diffusion increases, hence why it is better for a cell to have more surface area then to have more volume.
Temperature: temperature affects the rate of diffusion also, increases in temperature cause all of the molecules to move faster, hence why the rate of diffusion will increase. But if the temperature decreases the rate of diffusion will also decrease because the molecules will not be moving as fast.
Endocytosis is the process of taking particles into the cell by engulfing it as part of the cell membrane. Phagocytosis and pinocytosis are types of endocytosis (movement of particles into the cell), phagocytosis is the intake of solid particles by a cell and pinocytosis is the intake of liquid particles by a cell
Exocytosis is the movement of large amounts of material out of the cells using a vesicle
A hypotonic enviroment will cause water to move into the cell. Without the protection of a cell wall though, the animal cell will burst
A hypertonic environment will cause water to move out of the cell causing the cell to shrink in size.
isotonic environment will cause no net movement of water
The surface area affects cells greatly. If cells want to survive the increase their surface area by becoming smaller cells. The more surface area a cell has the faster the diffusion rate. The more volume that a cell has the smaller the surface area the>slower diffusion rate>less likely to survive.

Enzymes

Metabolism-The chemical processes that occurs within a living organism in order to maintain life
enzymes- Enzymes allow many chemical reactions to occur within the homeostasis constraints of a living system. Enzymes function as organic catalysts. A catalyst is a chemical involved in, but not changed by, a chemical reaction. Many enzymes function by lowering the activation energy of reactions.
Substrate-A reactant is a substance that participates in a reaction] the reactants in an enzymatic reaction are called the substrates for that enzyme
Coenzymes-Many enzymes require a nonprotein cofactor to assist them in carrying out their function. Coenzymes are cofactors that consist of organic molecules that bind to enzymes and serve as carriers for chemical groups or electrons. The protein portion of the enzyme accounts for its specificity and the coenzyme portion of the enzyme participates in the reaction. A coenzyme is generally a large molecule that the body is incapable of synthesizing without the ingestion of a vitamin.
Activation Energy-The term activation energy refers to the minimum amount of energy required for a chemical reaction to occur

The active site if where the enzyme and substrate fit together, seemingly like a key fits a lock. The active site undergoes a slight change in shape in order to accommodate the substrate. This is called induced fit model because the enzyme is induced to undergo a slight alteration to achieve optimum fit. 

 Enzyme activity increases as substrate concentration increases because there are more collisions between substrate molecules and the enzyme. As more molecules fill active sites, more product results per unit time. 

As temperature rises, enzyme activity increases. This occurs because higher temperature causes more effective collisions between enzyme and substrate. If the temperature rises beyond a certain point, enzyme activity eventually levels out and then declines rapidly because the enzyme denatured. An enzyme's shape changes during denaturation, and then it can no longer bind its substrate efficiently. 

Since enzymes are specific, a cell regulates which enzymes are present and / or active at any one time. Enzymes may be present that are not needed, or one pathway may negate the work of another pathway. Genes must be turned on to increase the concentration of an enzyme and turned off to decrease the concentration of an enzyme. 

Many enzymes require an inorganic ion or organic but non protein molecule to function properly; these necessary ions or molecules are called cofactors. The inorganic ions are metals such as copper, zinc, or iron. The organic, nonprotein molecules are called coenzymes. 

The thyroid glad is composed of a large number of follicles, each a small spherical structure made of thyroid cells filled with truuodothryronine (T3), which contains three iodine atoms, and thyroxine (T4), which contains four iodine atoms. To produce thyroxine and triiodothyronine, the thyroid gland actively acquired iodine. 

Vitamins are organic compounds that the body uses for metablic purposes but is unable to produce in adequate quantity. Many vitamins are portions of coenzymes, which are enzyme helpers. Coenzymes are needed in only small amounts because each can be used over and over again.