Ch. 06 KEY - An Introduction to Metabolism 2016 PDF

Preview

Summary

Answer key...

Description

Ch. 6. An Introduction to Metabolism Key Concepts for Ch. 6 6.1

An organisms metabolism transforms matter and energy.

6.2

The Eukaryotic change of a reaction tells us whether or not the reaction occurs spontaneously .

6.3

ATP powers cellular work by coupling exergonic reactions to endergonic reactions.

6.4

Enzymes speed up metabolic reactions by lowering energy barriers (ACTIVATION ENERGY).

6.5

Regulation of enzyme activity helps control metabolism.

1)

The sum total of all chemical reactions in an organism is called metabolism.

2)

A metabolic pathway begins with a starting molecule which is then altered in a series of defined steps, resulting in a certain product.

3)

The overall metabolic process involves two processes. A. Catabolic - pathways which release NRG together when complex molecules are broken down. (ex: cellular respiration) B. Anabolic- pathways which requires NRG to put together complex molecules (ex: synthesis of protein from amino acids)

4)

Bioenergetics is the study of how energy flows through living systems and is essential to look at in order to understand metabolic processes of the cell.

5)

Energy is the capacity to cause change. It is important because some forms of energy can be used to do work such as moving matter against opposing forces such as gravity and friction.  energy is the ability to rearrange matter

Forms of Energy

6)

Energy associated with the relative motion of objects is called kinetic

7)

Heat or thermal energy is associated with the random movement of atoms or molecules.

8)

An object that is not moving may still possess potential energy which is the energy it holds due to its position/location or structure.

 Molecules possess energy because of the arrangement of electrons in the bonds between their atoms.  The atoms of high energy reactants can be rearranged into lower-energy breakdown products.

Chemical energy refers to the potential energy available for release in a chemical reaction. The Laws of thermodynamics: 9)

10)

The study of the energy transformations that occur in a collection of matter is called thermodynamics.

11)

In an open system, energy and matter can be transferred between the system and its environment. Organisms are open systems, they absorb energy (eat molecules) and release heat.

12)

Define: 1st Law of ThermodynamicsEnergy can be transferred and transformed, but it can not be created or destroyed.

2nd Law of ThermodynamicsEvery energy transfer or transformation increases the entropy of the universe.

13)

A consequence of the loss of usable energy during energy transfers is that it makes the universe more disordered. Scientists use a quantity called entropy to measure disorder or randomness. *unusable heat is associated with increased entropy *Energy must be constantly added to offset entropy (maintain order)

14)

A reaction that is can proceed without requiring the input of energy*** – “is energetically favorable” and increases entropy of the universe is said to be spontaneous. ***not totally true – needs the input of some activation energy, but then can drive itself with -G*** see later in notes!!!

15)

A reaction that will happen only if energy is supplied and leads to a decrease in entropy is said to be nonspontaneous.

The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously 16)

17)

Free energy: the proportion of a system’s NRG that can perform work when temperature and pressure are uniform throughout the system. (G) G = Gfinal state – Ginitial state Gibbs Free Energy (Bozeman)

A spontaneous reaction that proceeds with the release of free energy is known as an exergonic reaction (-G)

Cellular respiration G = -686 kcal/mol *breaking bonds DOES NOT release energy, it REQUIRES energy. The release of energy in a chemical reaction occurs when bonds are broken and new bonds are formed and the products have less free energy than the reactants had (-G)

18)

Other reactions (nonspontaneous) can be made to proceed only with the addition of free energy are known as endergonic (+G) Photosynthesis G = 686 kcal/mol

Energy Dynamics Activity (Campbell)

Equilibrium and metabolism 19)

Reactions in isolation eventually reach equilibrium and can do no work.

20)

Metabolic equilibrium =

21)

A cell that reaches metabolic equilibrium is dead!!!

22)

Disequilibrium is maintained because the products of one reaction do not build up, but are used in another reaction or expelled as waste from the cell.

ATP powers cellular work by coupling exergonic reactions to endergonic reactions 23)

24)

Three main types of work in a cell are: Chemical work: the pushing of endergonic reactions a. b.

Transport work: the pumping of substances across membranes

c.

Mechanical work: contracting muscles, movement

Energy coupling: The use of an exergonic reaction to power an endergonic reaction. ATP is responsible for these coupled reactions in organisms. Know the components of ATP!

25)

The bonds of ATP can be broken by hydrolysis this is considered an exergonic reaction (G = -7.3 kcal/mol) in cellular respiration.

26)

The hydrolysis of ATP under cellular conditions releases -13 kcal/mol

27)

The three phosphate groups in ATP have a negative charge which contributes to the instability of the molecule and high free energy. This portion of the molecule could be compared to a compressed spring.

28)

With the help of enzymes, cells are able to use energy released by ATP hydrolysis to drive a chemical reaction that is endergonic (nonspontaneous).

29)

If the G of the endergonic reaction is less than the amount of energy released by ATP hydrolysis, the two reactions can be coupled so that the overall reaction is exergonic (spontaneous).

30) The key to coupling exergonic and endergonic reactions is the formation of a phosphorylated intermediate which is more reactive (less stable).

ATP – ADP Cycle 31)

ATP can be regenerated at an astonishing rate. A muscle cell will recycle all its ATP in less than a minute (10 million molecules of ATP consumed and regenerated per second per cell)

32)

The energy required for the regeneration of ATP comes from exergonic (catabolic) reactions in the cell (cell respiration)

33)

ATP is converted to ADP and a phosphate which is more stable.

34)

The loss of a phosphate makes ADP have less NRG and be more stable.

35)

The regeneration of ATP is an endergonic reaction while the breaking of ATP is an exergonic reaction..

Enzymes speed up metabolic reactions by lowering energy barriers: 36)

Rate of Reaction: the speed at which a reaction moves towards equilibrium *controlled by concentration gradients and enzymes

37)

An enzyme is a macromolecule that acts as a catalyst to speed up a reaction without being consumed by the reaction. Examples: (-ase) a) sucrase (breaks down sucrose)

b) protease (breaks down protein) c)

Lipase (breaks down lipids)

38)

The initial investment of energy necessary to break bonds in the reactants and get the reaction started is called the activation energy EA. This is often supplied in the form of heat that the reactant molecules absorb from the surroundings.

This energy allows the reactants to reach their transition state at which point they are unstable and primed to break and reform bonds. ***reactions with a low activation energy requirement proceed at a very fast rate, while those with a high requirement proceed at a slow rate***

39) Why are spark plugs essential for cars to run? Spark plugs provide the activation energy for gasoline and oxygen to reach their transition state and react (surmount the activation energy). Then the spontaneous reaction occurs.

40)

Why is the barrier of activation energy essential to life? Without a barrier most reactions would occur spontaneously and could not be controlled. This would result in a loss of internal balance or homeostasis leading to cell death.

41)

Adding heat will speed up a reaction but is inappropriate for most biological systems because: A) High temperatures denatures proteins and kills cells. B) It would speed up all reactions not just the ones needed.

42)

An enzyme catalyzes a reaction by lowering the activation energy needed enabling the reactant molecules to absorb enough energy to reach the transistion state at moderate temperatures.

43)

Enzymes are very specific, hasten reactions that would occur slowly, and are NOT consumed in these reactions.

44)

The reactant an enzyme acts on is called the substrate.

45)

The enzyme binds to its substrate(s) forming an enzyme-substrate complex.

46)

Only a restricted region of the enzyme, called the active site actually binds with the substrate.

47)

The specificity of an enzyme is attributed to the compatible fit between the active site and the substrate.

48)

The active site does not fit rigidly like a lock and key. As the substrate enters the active site interaction of the R groups of the amino acids causes the enzyme to change its shape slightly so that the active site fits even more snuggly around the substrate. This is called induced fit.

49)

Enzymes can be catabolic (above) or anabolic (right) depending on whether the break down or combine molecules respectively.

50)

4 Enzyme mechanisms that lower activation energy 1) The active site provides a template for the substrates to come together. 2) The enzyme stresses and bends the chemical bonds that must be broken thus lowering activation energy. 3) The active site provides a microenvironment that is conducive for the reaction to proceed.

4) Direct participation of the active site in the chemical reaction.

38) Factors affecting the rate of reaction A) Substrate concentration Increasing substrate concentration will increase the rate of reaction in direct proportion until all enzyme molecules have their active site engaged. At that point the enzyme is said to be saturated. The only way then to increase the rate of reaction is to increase the amount of enzyme.

B) Enzyme concentration Increasing the enzyme concentration will increase the rate of reaction as long as there is enough substrate for enzymes to work on. a. Draw the curve that you might think would represent the rate of reaction as more and more enzyme is added to a constant level of substrate. Explain

C) Temperature – enzyme rate will increase until a point where the enzyme denatures. (in humans this optimal temp. is normally 37oC)

C) pH – most work best at a pH of 7 but will vary depending on the enzyme ex. Pepsin in the stomach -----> pH 2 Trypsin in the intestine -----> pH 8

39)

Many enzymes require non-protein helpers for catalytic activity. A) Coenzymes are organic molecules that aid enzymes in lowering activation energy. Many of these are vitamins that we get in our diet. B) Inorganic enzyme helpers are called cofactors and are usually minerals. Enzyme Inhibitors 40)

If an inhibitor attaches to the enzyme by covalent bonds it is usually irreversable but if it attaches by weak interactions the inhibition is reversable.

41)

Competitive inhibitors reduce the productivity of enzymes by blocking substrates from entering the active site. This type of inhibition can be reversed by increasing the concentration of the original substrate. Example: carbon monoxide

42)

Noncompetitive inhibitors do not directly compete with the substrate for active sites. Instead they bind to another part of the enzyme changing the enzyme’s shape so that it is less effective. This site of attachment is called the allosteric site.

Allosteric Regulation of Enzymes

43)

Allosteric regulation is the term used to describe any case in which a protein’s function at one site is affect by the binding of a regulatory molecule to a separate site. It may result in either

a. Activation

b. Inhibition

44)

In cooperativity, the binding of one substrate molecule can stimulate the binding or activity at other active sites.

45)

In feedback inhibition, the end product of a metabolic pathway allosterically inhibits the enzyme from a previous step in the pathway. Most commonly used to maintain homeostasis by preventing overproduction of products in a cell. (negative feedback) Feedback Pathways

Using a series of arrows, DRAW the branched metabolic reaction pathway described by the following statements. Then answer the question at the end. Use red arrows and minus signs to indicate inhibition. L can form either M or N M can form O O can form either P or R P can form Q R can form S O inhibits the reaction of L to form M Q inhibits the reaction of O to form P S inhibits the reaction of O to form R.

Which reaction would prevail if both Q and S were present in the cell at high concentrations? A) L  M B) M  O C) L  N D) O  P...