Anatomy and Physiology 12 - Unit 2: Homeostasis II

here we go again

What is an enzyme?

It is a protein that speeds up a chemical reaction without a temperature change. It acts as a catalyst for the reaction (speeds it up without being used up or changed). It is the site of the chemical reaction and holds substrates together long enough for them to react.

What are the functions of an enzyme?

1. Maintain homeostasis — living organisms regulate their internal environment by controlling regulation mechanisms. These are needed for these regulation mechanisms.

2. Metabolism — all chemical reactions are occurring constantly in cells to maintain homeostasis

What are the components of an enzyme?

1. apoenzyme: protein part of the enzyme, specific to substrate, where the reaction is catalyzed (contains active site)

2. active site: location where substrates bind on enzyme

3. cofactor (coenzyme): organic/non-protein part of the enzyme that assists enzyme by accepting ion from/donating ions to substrate (ex. metal ions)

and

4. substrate: reactants in an enzyme catalyzed reaction

5. vitamins: components needed for synthesis of coenzymes

How do enzymes work?

Induced fit theory:

• The enzyme site is not the exact same shape as substrate, but when binding the substrate, the enzyme undergoes a slight change in shape of the active site.

• After the reaction, the enzyme-substrate complex (structure formed when enzyme binds substrate) separates and the enzyme re-assumes original shape, making it ready to catalyze another reaction

What is the equation for an enzyme-catalyzed reaction?

Enzyme + substrate → Enzyme/Substrate Complex → Enzyme + Product

How do enzymes affect a reaction?

They lower activation energy by bringing the substrate molecules together and holds them together long enough for reaction to take place.

What is a metabolic pathway?

It’s an orderly, step-wise series of chemical reactions from reactants to products where one reaction leads to another. Each step requires a specific enzyme.

How do metabolic pathways work in the body?

• It is not possible in biological systems to have a single reaction produce complex molecules from simple reactants

• Many intermediates are still needed, and one path may lead to several other paths

• The intermediate product of one path could be the starting reactant for another path

• Having more than one step means more places where the overall reaction can be controlled

What is the metabolism hormone?

Thyroxin, from the source gland of the thyroid and composed of protein.

What does the metabolism hormone do?

• increases metabolic rate by increasing oxidation rate (oxygen uptake) in cells

• increase of thyroxin in blood = increase in ATP production in cells

What is the feedback loop where the metabolism hormone is involved?

1. Hypothalamus secretes Thyroid Stimulating Hormone (TSH)

2. Pituitary Gland secretes TSH

3. Thyroid Gland secretes thyroxin

4. Thyroxin travels back to Hypothalamus and Pituitary Gland and it loops again

What factors affect enzyme activity?

1. pH — each enzyme works optimally in a preferred pH range. If pH is out of range (too high or low), the enzyme denatures (loses normal shape and ability to form ES complex)

2. Temperature — Lower temperature slows rate of reaction, collision rate of enzyme and substrate, and vice versa. However, very low temperature does not normally denature enzyme. High temps over 45degreesC denatures enzymes (they can’t recover from this

How does substrate concentration affect rates of reaction?

• High concentration of substrates = increased reaction rate

• After a certain concentration of substrates is reached, the rate will not increase anymore

• Once the enzyme is “saturated” with substrate (all active sites filled), it cannot work any faster and the reaction rates will level off

• Low concentration of substrates = decreased reaction rate

How does enzyme concentration affect rates of reaction?

• We work under the following assumption: there are typically millions more substrate molecules than enzyme molecules

• High concentration of enzymes = increased reaction rate

• Low concentration of enzymes = decreased reaction rate

• No more substrate left = decreased reaction rate (rarely happens)

• linear relationship

What are inhibitors?

Molecules that disrupt the formation of E/S complex