Metabolism Flashcards

1
Q

What happens in a biological chemical reaction?

A

For chemical reactions in biological systems (facilitated by enzymes), we call reactant “substrate”: Substrate → Product

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2
Q

What is metabolism?

A

The sum of all chemical reactions performed by a

cell or organism

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3
Q

What happens to individual reactions during metabolism?

A

» catalysed by specific enzymes
» connected into “metabolic pathways”, where the products of one pathway become the substrates for others
• Pathways can be linear, reversible, circular, branched

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4
Q

What are the two types of Metabolic pathways?

A

Anabolic (biosynthetic) and Catabolic (degradative)

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5
Q

What is an anabolic metabolic pathway?

A

(biosynthetic)
» Synthesis of more complex compounds and molecules from simpler ones
» eg, sugars from CO2 during photosynthesis, or proteins from amino acids

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6
Q

What is a Catabolic metabolic pathway?

A

(degradative)
» Breakdown of complex molecules and compounds into simpler ones
» eg, amino acids from proteins, or oxidation of sugars to CO2 during respiration

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7
Q

What is Gibbs free energy (G)

A
  • Energy stored in a system
    » Measured in kcal/mol (or kJ/mol)
  • More complex systems have more G
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8
Q

What does ΔG mean?

A

Change in system energy

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9
Q

What is the ΔG for Catabolic reactions?

A
Catabolic reactions
» Release energy
» “Exergonic”
» “Spontaneous”
» Gproduct < Gsubstrate, so ΔG<0
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10
Q

What is the ΔG for anabolic reactions?

A
Anabolic reactions
» Require energy
» “Endergonic”
» “Non-spontaneous”
» Gproduct > Gsubstrate, so ΔG>0
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11
Q

What are the three kinds of work a cell performs?

A

» Chemical: endergonic reactions
» Transport: pumping across membranes against the concentration gradient
» Mechanical: contraction of muscle cells, movement of chromosomes during cell division, beating of cilia

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12
Q

How is the energy paid for during the different kinds of work a cell does?

A

Harvesting the energy stored in ATP

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13
Q

What is Adenosine Triphosphate and what is it composed of?

A

The currency of cells also known as ATP and it is composed of:
» Nucleotide base adenine
» Ribose sugar
» 3 linked phosphate groups

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14
Q

What releases energy in the ATP?

A
  • O-P bonds unstable, and release energy
    (exergonic) when broken down
    » ATP + H2O → ADP + Pi
    » ΔG = -7.3 kcal/mol
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15
Q

Draw the ATP cycle

A

Do this in your work book, refer to the back for the answer.

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16
Q

What happens in the ATP cycle?

A

Energy released by breakdown reactions (catabolism) in the cell is used to phosphorylate ADP, regenerating ATP. Chemical potential energy stored in ATP drives most cellular work.

17
Q

Where does all energy come from?

A

The sun. Energy flows into an ecosystem as sunlight and ultimately leaves as heat, while the chemical elements essential to life are recycled.

18
Q

What are enzymes?

A

Most enzymes are proteins
» Exception: some RNA-based (eg, ribozyme*)
- Enzymes speed up chemical reactions by lowering energy barriers, making life possible.
» “Catalyst” = a substance that increases the rate of a reaction without being consumed by the reaction

19
Q

What do enzymes do?

A
  • Facilitate transformation of initial substance (substrate) into different molecules (products)
  • Enzyme names (usually ending in –ase) indicate their function:
    » Lipase = breaks down lipids
    » Protease = breaks down proteins
    » Synthase = enzymes that build molecules
    » Isomerase = enzymes that rearranges a molecule into its isomer (ie, a different form)
20
Q

What is an activation energy?

A

Difference b/w energy level of substrate and transition

state

21
Q

What is the transition state of a chem reaction?

A

Transition state is highest energy state

22
Q

What is the order of a chemical reaction?

A

Substrate → transition state → product(s)

23
Q

What is the difference between a catalysed reaction and an uncatalised reaction?

A

Catalysed has a lower activation evergy for the transition state because an ezyme is being used to speed up the reaction.

24
Q

Why is it important to living systems that chemical reactions should have activation energies?

A

Other wise everything would happen at once and we would spontaneously combust because too much energy is being used at the same time.

25
How do you pay activation energy?
``` - Abiotic » Heat, pH gradient, sunlight etc ... - In cells, combination of » Lowering the energy costs (with enzymes) • Bringing substrates together • Putting torque on the substrate • Providing proper chemical micro-environment • Adding or removing functional group » ATP, the cellular energy currency ```
26
How do enzymes work?
Step 1: Substrate enters active site; enzyme changes shape so that its active site enfolds the substrates (induced fit) Step 2: Substrates are held in the active site by weak interactions, such as hydrogen bonds and ionic bonds Step 3: Substrates are converted to products Step 4: products are released Step 5: Active site is available to new substrates
27
What happens to the enzymes shape after the reaction?
Enzymatic reaction does not permanently change the enzyme’s chemistry or structure » Often changes its shape (“conformation”) during the reaction, but reverts back to original conformation once reaction complete
28
Can any enzyme react with any substrates?
Active site is substrate specific » There is only one correct substrate » Think “enzyme = lock, substrate = key” » Pharmaceutical drugs work by “copying the key”
29
Some enzymes require additional help to perform the biochemical reaction, where do they get it from?
» Co-factor = inorganic molecule that assists chemical transformation of substrate → products • Metal ions, such as iron (Fe2+ and Fe3+), magnesium (Mg2+) and zinc (Zn2+), which help with electron transfer » Co-enzyme = small organic molecule that assists in chemical transformation • Vitamin C, ATP, NAD+, NADP+, coenzyme A, etc …
30
Enzymes require optimum environments, what are some things that affect this environment?
pH, temperature, etc...
31
Chemical chaos would result if all of a cell’s metabolic pathways were operating all the time, how do cells stop this from happening?
- Cells regulate enzymes by turning them on or off » Natural regulation (methylation, phosphorylation, proteolytic cleavage) is usually reversible » Some poisons (eg, nerve gas) or drugs (eg, antibiotics) can cause irreversible enzyme inhibition - Often the products will act as inhibitor » “Feedback inhibition”
32
What is an inhibitor?
Substance which slows down or prevents a particular chemical reaction or other process or which reduces the activity of a particular reactant, catalyst, or enzyme.