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Biochemistry > Exam 3 November 23 Lecture > Flashcards

Exam 3 November 23 Lecture Flashcards

1
Q

How is the keto and the gluco world connected?

A

by 1 step: pyruvate being converted to acetyl CoA (this step is irreversible so can’t go back to pyruvate) → can’t utilize acetyl CoA to make pyruvate

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2
Q

When we’re hungry, what does the liver do?

A

makes glucose during gluconeogenesis

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3
Q

What happens when there is plenty of acetyl CoA?

A

we make fatty acids

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4
Q

What happens when there is a lot of fatty acids?

A

we break down fatty acids to make acetyl CoA

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5
Q

What do unsaturated fatty acids (aka kinks) do to the melting temperature?

A

lowers the melting temperature

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6
Q

What does it mean if a fatty acid is essential?

A

our body needs them but the body is unable to make them so we get them from the foods we eat

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7
Q

What are eicosanoids?

A

have 20 carbons and are like hormones such as prostaglandins that function in inflammation

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8
Q

What is excess energy stored as?

A

fat → fatty acids are synthesized from acetyl CoA in which the liver and adipose tissues convert glucose to fatty acids and then to triacylglycerol

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9
Q

How is triacylglycerol released into the bloodstream by the liver?

A

it is packed in lipoproteins (VLDL) → lipoproteins are not soluble so they can build up and block the bloodstream

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10
Q

What type of cells store triacylglycerol?

A

adipocytes (fat cells)

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11
Q

What is the difference between white fat cells and brown fat cells?

A

white fat cells are primarily composed of triacylglycerol and is used for storage like tiny tanks while brown fat cells have lots of mitochondria to help generate heat since these type of cells generate body heat so that when it’s cold, it helps the body maintain its temperature → infants have lots of brown fat cells but we lose them as we age

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12
Q

Why is the transfer of acetyl CoA crucial?

A

fatty acid synthesis occurs in the cytosol but acetyl CoA is produced in the mitochondria → acetyl CoA is needed to be brought into the cytosol but it has no transporter and is a large molecule → needs to be converted to citrate to be transported to the cytosol

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13
Q

What happens when there is a lot of acetyl CoA in the mitochondria?

A

the TCA cycle is active to make citrate and citrate is transported to the cytosol so that it can be converted to acetyl CoA to make fatty acids

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14
Q

What is the difference between malonyl CoA and acetyl CoA?

A

malonyl CoA has 3 carbons but acetyl CoA has 2 carbons

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15
Q

What is the commitment step of fatty acid synthesis?

A

the conversion of acetyl CoA to malonyl CoA (is also the rate limiting step and is a highly regulated step and requires ATP)

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16
Q

How is the activity of acetyl CoA carboxylase regulated?

A

activated by citrate and isocitrate

inhibited by acyl CoAs

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17
Q

What is malonyl CoA used for?

A

as a substrate for fatty acid synthesis → therefore, it inhibits fatty acid oxidation

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18
Q

What happens if there are high levels of malonyl CoA?

A

we are synthesizing fatty acids which means we should not be breaking down fatty acids → malonyl CoA inhibits fatty acid oxidation

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19
Q

What do high levels of citrate mean?

A

we have lots of acetyl CoA which signifies we need to make fatty acids

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20
Q

What do high levels of acyl CoA mean?

A

we don’t need to make fatty acids → we need to break down fatty acids to make energy

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21
Q

What are the steps to fatty acid synthesis?

A

starts with acetyl CoA adding 2 carbon units at a time → the growing fatty acids are carried by acyl carrier protein (ACP) or fatty acid synthase through a covalent bond (thioester) → carboxyl group of malonyl CoA is released as CO2 during synthesis → final product is released from ACP by hydrolysis

22
Q

How many NADPH are used for fatty acid synthesis?

A

two NADPH are used per cycle

23
Q

Fatty acid synthase is what kind of enzyme?

A

multifunctional → huge enzyme with multiple subunits

24
Q

How are the growing fatty acids released?

A

when the chain grows to be 16 carbons → becomes palmitate and the thioester bond is cut and the molecule is released

25
Q

How is NADH and NADPH different?

A

structurally similar and have similar properties (can reduce compounds) but NADPH is mostly used for synthesis (synthesizes molecules) while NADH is usually used to make energy from ETC (delivers energy to ETC to create proton gradient to then make ATP)

26
Q

What is saturated fat?

A

a straight chain and is like solid fat (examples are butter and lard)

27
Q

What is unsaturated fat?

A

kinked chain and is like liquid fat such as cooking oils

28
Q

What is the major fat in our diet and in adipose tissues?

A

triacylglycerol

29
Q

How is triacylglycerol hydrolyzed?

A

lipases hydrolyze triacylglycerol to glycerol and three fatty acid molecules → glycerol is converted to an intermediate for glycolysis or gluconeogenesis and the fatty acids are used for energy production through fatty acid oxidation

30
Q

How many molecules of glucose can be made from 2 triacylglycerols?

A

1 glucose molecule → since triacylglycerol has 3 carbons while glucose has 6 carbons and when triacylglycerol is hydrolyzed, one glycerol molecule is made (contains 3 carbons)

31
Q

Where does fatty acid synthesis and oxidation occur?

A

synthesis occurs in the cytosol while oxidation occurs in the mitochondria

32
Q

How are fatty acids activated?

A

activated by forming acyl CoA → acyl CoA is used for fatty acid oxidation or triacylglycerol synthesis

33
Q

What is the role of acyl CoA in fatty acid oxidation?

A

acyl CoA in the cytosol needs to be converted to acylcarnitine for transport into the mitochondria for fatty acid oxidation → the rate limiting step for fatty acid oxidation!

34
Q

What is acylcarnitine?

A

bound to acyl CoA and has a transporter to bring it into the mitochondria to then become acyl CoA

35
Q

What is carnitine?

A

necessary for fatty acid oxidation so some people believe carnitine is a fat burner → taking more of carnitine will NOT increase fat burning

36
Q

The conversion of acyl CoA to acylcarnitine is carried out by what enzyme?

A

carnitine palmitoyltransferase I (CPT I) → which is inhibited by malonyl CoA so if malonyl CoA is high, we are synthesizing fat so CPT I is inhibited by malonyl CoA

37
Q

If a fatty acid has 16 carbons, how many fatty acids can it generate?

A

8 → two carbon units at a time

38
Q

What happens during β-oxidation?

A

two carbon units are removed from acyl CoA as acetyl CoA (C2) at a time → NADH, FADH2, and acetyl CoA are produced (total of 4 ATP)

39
Q

At the end of the cycle, fatty acids with an odd number of carbons produce a propionyl CoA (C3).

A

examples:
C16 fatty acid → 8 acetyl CoA
C17 fatty acid → 7 acetyl CoA + 1 propionyl CoA

40
Q

The acetyl CoA produced from β-oxidation is used for what?

A

used as fuel for the TCA cycle or as a substrate for the synthesis of ketone bodies and cholesterol

41
Q

How is the conversion of propionyl CoA (3 carbons) to succinyl CoA (4 carbons) an anaplerotic reaction?

A

succinyl CoA is an intermediate of the TCA cycle and propionyl CoA supplements the TCA cycle → TCA cycle runs with acetyl CoA as fuel and could always add more intermediates along the way

42
Q

The oxidation of palmitate to acetyl CoA produces how much ATP?

A

26 ATP

43
Q

The synthesis of palmitate from acetyl CoA requires how much ATP?

A

49 ATP

44
Q

Why does synthesis use of more energy than the breakdown of fatty acids?

A

synthesizing and breaking down and synthesizing and breaking down uses up energy (or energy is lost by heat)

45
Q

If oxidation is on, synthesis should be what?

A

off → both reactions have cross talk so only one of the reactions should occur at one time (so not both at once)

46
Q

What do humans synthesize first?

A

saturated C16 (palmitate)

47
Q

How can palmitate be elongated?

A

it can be elongated further by enzymes other than fatty acid synthase → example is stearate (C18)

48
Q

Double bonds are added by what?

A

desaturases

49
Q

How are double bonds added?

A
  1. humans can add double bonds only up to the 9th carbon
  2. desaturases for 4,5, 6 positions act only on fatty acids with a double bond at 9th carbon → can only add double bonds in certain locations with desaturases
50
Q

Why are ⍵-3 and ⍵-6 fatty acids essential?

A

they have double bonds in the beginning part of the molecule so our bodies cannot make them and they come from the diet

Biochemistry (18 decks)

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