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MSAP 2015 > BIOCHEMISTRY: RESPIRATORY SYSTEM > Flashcards

BIOCHEMISTRY: RESPIRATORY SYSTEM Flashcards

1
Q

What type of structre is α-helix and how is it stabilized?

A

The α-helix: an example of secondary structure

•Stabilized by hydrogen bonding

–Involves the atoms that participate in the peptide bond

–Repetitive hydrogen bonding

•Amino acid side chains stick out to the side of the helix

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2
Q

What is the structure of β-sheets and how is it stabilized?

A

The β-sheet: an example of secondary structure

Stabilized by hydrogen bonding

Involves the atoms that participate in the peptide bond

Repetitive hydrogen bonding

Amino acid side chains stick out above and below the plane of the sheet

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3
Q

Describe globular proteins.

What’s special about the surface and interior?

What are their functions?

A

Globular proteins which are water soluble are approximately a spherical shape and are generally characterized by having…

•Polar aa side chains on surface

–Creates good water solubility

•Non polar aa side chains in interior

–Hydrophobic core

•Variety of secondary structure type

–Combo of b-sheet, a-helix, and turns

•Some kind of biological / metabolic function

–Catalytic

–Regulatory

–Transport

Most globular proteins are a combination of alpha helix and beta-sheet

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4
Q

The figure shows a link between two amino acids in a polypeptide. What is a consequence of this bonding arrangement?

A.Limited bond rotation between Cα1 and carbonyl carbon

B.Limited bond rotation between N and carbonyl carbon

C.Loss of amino acid water solubility

D.Minimized distances between amino acid side chains

E.Capability to form hydrogen bonds between Cα1 and Cα2

A

B. Limited bond rotation between N and carbonyl carbon

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5
Q

What is the heme?

A

Heme is the porphyrin ring with the ferrous ion in the center

Globular heme proteins contain heme as prosthetic group

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6
Q

What are functions of globular hemeproteins?

A
  • Functions of globular hemeproteins include:
  • May be found as part of an enzyme active site

–Cytochrome p450 enzymes in liver

•Transport of O2

–Hemoglobin in the red blood cell)

• Storage of O2

–Myoglobin in the muscle cell

•Electron carriers

–Required for mitochondrial electron transport chain

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7
Q

Why is globin an unusual protein structure?

A
  • The globin protein monomer is mostly composed of α-helix
  • A few bends or turns are present
  • Globin is an unusual structure protein in that it is devoid of β-sheet
  • Most proteins are a combination of α-helix and β-sheet
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8
Q

How is hemoglobin constructed?

A

Human hemoglobin is a tetramer of 4 polypeptide chains

  • Hemoglobin A (HbA) is a pair of identical αβ dimers (α2β2 tetramer)
  • The heme groups are widely spaced
  • Access to the ferrous ion is through a channel in the protein
  • Appreciate that there are extensive interactions between the subunits

–Hydrophobic

–Ionic

–Hydrogen bonds

•4 globin monomers means that 4 O2 molecules may be carried on Hb

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9
Q

What type of interactions are between the alpha2 & beta 2 subunits in human hemoglobin?

A
  • Hemoglobin A (HbA) is a pair of identical αβ dimers (α2β2 tetramer)
  • The heme groups are widely spaced
  • Access to the ferrous ion is through a channel in the protein
  • Appreciate that there are extensive interactions between the subunits

–Hydrophobic

–Ionic

–Hydrogen bonds

•4 globin monomers means that 4 O2 molecules may be carried on Hb

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10
Q

How does secondary structure happen?

A

secondary structure is due to partial negative and positive charge

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11
Q

What are the differences between myoglobin and hemoglobin?

A

Myoglobin

found in the muscle (purpose to store O2), is a monomer, mostly composed of alpha helix, no beta sheets, has proximal and distal histidine, Fe2 heme has 6 bonds (4 to Nitrogen, 1 to globin protein and 1 for Oxgen), hyperbolic curve

Hemoglobin

found in red blood cells (purpose to transport O2), is a tetramer (4 polypeptide chains), heme groups widley spread apart, can carry 4 O2,

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12
Q

What is the difference between the taut and relaxed state?

A

taut state = no oxygen

relaxed state = oxgen bound

As hydrogen binds to hemoglobin, H bonds break and affinity for oxygen increases.

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13
Q

Why is hisidine important in the blood?

A

it has acid/base characterisitics b/c it’s pKA is close to physiological pH

  • help buffer blood pH
  • Regulate O2 affinity in response to pH
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14
Q

What is the importance of side chains found at the interface between alpha/beta-dimers?

A

the side chainsc an form hydrogen bonds/ionic interactions which change oxygen affinity

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15
Q

Why is O2 a positive allosteric regulator of oxygen binding?

A

Binding of one O2 molecule promotes binding of another O2 molecule This is called cooperative ligand binding.

We can therefore say that O2 itself is a positive allosteric regulator of oxygen binding, because binding of O2 at one site, increases affinity for O2 at another site

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16
Q

Which way does the O2 dissociation curve shift with decreases and increased pH and explain the shift in terms of increased and decreased affinity.

A

decreased pH cause a shift to the right (increased PCO2 leads to decreased pH)

As pH decreases, hemogoblin displays a reduced affinity for O2

This is important because we want O2 to fall off where it’s needed in the muscles (areas of increased CO2)

17
Q

How does 2,3 - BPG help regulate oxygen?

Consider how pH may affect the histidine side chains in the 2,3-BPG binding pocket.

A

2,3 - BPG will either come or go to help reuglate oxygen depending upon the parital pressures and where the positive chages are.

2,3- BPG have negative charges and positively charged side chains of a.a. form a pocket for 2,3-BPG to bind.

At higher pH, histidine is less likely to be protonated. At lower pH, there are more H+ protons and it is more likely to be protonated taking a + charge in acidic conditions (tissues actively metabolzing).

You’re more likely to have 2,3-BPG at the interface b/w our alpha/beta dimers and this will help promote the taut state. This will help squeeze out O2, delivering it to the tissues (decreased affinity for O2).

  • 2,3-BPG allows the formation of additional salt bridges between the αβ / αβ dimers
  • This creates a driving force for Hb to assume the deoxyHb structure (taut form)

–Promotes unloading O2 in the tissues

18
Q

How does increases and decreases in 2,3- BPG affect sigmoidal O2 binding curve?

A

If no 2,3-BP will end up w/ alterations and shifts left. W/o hemoglobin, can’t function as a transport protein. Hemoglobin will act as a sink and will hold on to O2. A person w/ higher leves of 2,3-BPG, has more reduced affinity for O2 and it will give O2 away more easily.

  • Higher levels of 2,3-BPG promote oxygen release to the tissues
  • Decreases the affinity of Hb for oxygen
  • 2,3-BPG is a negative allosteric effector
19
Q

What are allosteric effectors with regards to regulation of O2 deliver by Hb?

A

•Regulation of O2 delivery by Hb depends on allosterism (“other site”) effectors:

–pO2

–pH of environment

–pCO2 (which influences pH, and taut/relaxed state)

–2,3-bis-phosphoglycerate availability

–increased temperature creates a right shift

•Myoglobin is not regulated in this way

20
Q

Why should decreased pH shift curve to the right?

How does temperature effect curve?

A

With decreased pH, there are is higher CO2. A right shift means there is a lower affinity for oxygen. This means O2 will dissasociate in places where oxygen is needed. (High CO2 areas)

Increased temp = right shift

decreased temp = left shift

21
Q

What two factors determine how much oxygen is delivered to tissues?

A

Oxygen delivery to tissues depends on the following two factors:

  • Cardiac Output = Heart Rate x Stroke Volume
  • Total oxygen content of blood

Oxygen delivery to the tissues can be estimated with the following equation:

Oxygen Delivery = Cardiac Output (L/min) x Oxygen Content of Blood (mL of O2)

22
Q

In the oxy-hemoglobin curve, what is a left shift? What does this facilitate?

A

A “left shift” of the oxygen hemoglobin dissociation curve refers to when the p50 < 26.7 mmHg. A left shift reflects an increase in hemoglobin’s affinity for O2, which facilitates loading of O2 in the lungs.

A left shift of the oxygen hemoglobin curve can be caused by:

Decreased temperature

CO Poisoning

Decreased [H+] (increased pH)

Decreased [2,3-BPG]

23
Q

What does the Bohr effect describe? What are the 4 factors that influence this effect?

A

The Bohr effect describes the changes in hemoglobin’s affinity for oxygen in the presence of the following metabolic and environmental factors:

  • Temperature
  • [H+]
  • [2,3-BPG]
  • [CO2]

The Bohr effect helps explain how optimal loading/unloading of oxygen at the lungs and tissues is achieved:

Decreased temperature, [H+], [2,3-BPG], and [CO2] increases hemoglobin’s affinity for O2, thereby promoting the loading of O2 in the lungs

In the tissues, increased temperature, [H+], [2,3-BPG], and [CO2] decreases hemoglobin’s affinity for O2, thereby promoting the unloading of O2

​Note: Fetal hemoglobin is NOT influenced as strongly by 2,3-BPG as adult hemoglobin. This allows for fetal hemoglobin to have a greater affinity for O2, which helps fetal blood maintain adequate oxygenation in utero.

The Haldane effect:

In the lungs, oxygenation of Hgb promotes dissociation of H+ that is bound to Hgb. The resulting increase in free [H+] facilitates CO2 formation and expiration at the lungs via the above reaction catalyzed by carbonic anhydrase (H+ + HCO3- → H2CO3 → CO2 + H2O).

24
Q

If there is a decrease in the concentration of hemoglobin in the blood, how will that affect the total oxygen content of the blood? How will that affect the hemoglobin saturation percentage?

A

Under normal circumstances, the vast majority of the oxygen transported through the blood is bound to and carried by hemoglobin. If the concentration of hemoglobin decreases (ex: anemia), there will be a decrease in total oxygen content of the blood but no change in the hemoglobin saturation percentage.

Carbon monoxide (CO) binds to hemoglobin with a much greater affinity than O2. In CO poisoning, because the CO binds to hemoglobin, the hemoglobin saturation % and amount of O2 dissolved in the blood are normal. However, because CO takes up binding sites on hemoglobin that would normally carry oxygen the total oxygen content of the blood is decreased.

For every 1g/dL of hemoglobin (Hgb), 1.34mL of O2 can be carried by hemoglobin when fully saturated.

The normal [Hgb] in blood varies based on gender, but it can be approximated to ~15 g/dL (12-16 in females, 14-17 in males). Given this normal hemoglobin concentration, the O2 binding capacity of blood in the average person is ~ 20.1mL.

The amount of O2 dissolved in the blood depends on:

Atmospheric pressure (pressure of inspired air)

Solubility of oxygen, which is inversely related to temperature

Partial pressure of oxygen in plasma (PaO2)

Together, this can be represented as 0.003PaO2

If more than 5 g/dL of the hemoglobin in the blood is deoxygenated, cyanosis results.

25
Q

A standard hemoglobin-O2 dissociation curve is shown below. Which of the following conditions will shift this curve to the right?

A Decreased 2,3DPG

B Living in higher altitude

C Hypothermia

D Fetal hemoglobin

E Decreased [H+]

A

When p50 > 26.7 mmHg, the curve shifts to the right and has less affinity of hemoglobin for O2. This facilitates unloading of O2 to tissues. Right shift occurs with ↑ temperature, ↑ H+ (↓ pH), ↑ altitude (lower atmospheric O2), and ↑ 2,3 DPG. Left shift results in increased O2 affinity and occurs with ↓ temperature, ↓ H+, ↓ 2, 3 DPG and in fetal hemoglobin.

Recall that Right shifters of the Hgb dissociation curve can be remembered with mnemonic: “CADETs face right”

  • CO2 ↑
  • Acidosis, Anemia
  • 2,3-DPG
  • Elevation
  • Temperature ↑

When P50 > 26.7mmHg, the hemoglobin dissociation curve is said to exhibit a “right shift.” With a right shift, hemoglobin has less affinity for O2, which facilitates unloading of O2 in the tissues. Right shift occurs with:

  • Increased temperature (ex: tissues with increased metabolic activity)
  • Increased [H+] (decreased pH)
  • Higher altitude
  • Increased [2,3-BPG] (aka 2,3-DPG
  • CHRONIC anemia, which causes an increase in [2,3-BPG]

The factors that cause a right shift in the oxygen hemoglobin dissociation curve can be remembered with mnemonic: “CADETs face right”

  • CO2 (increased [CO2] )
  • Acidosis, Anemia
  • 2,3-DPG
  • Elevation
  • Temperature increase
26
Q

In an obstructive lung disease, how is inspiration affected? How is expiration affected?

A

In obstructive lung diseases inspiration is normal, but airway obstruction causes impairment of expiration (expiration is prolonged). This can result in air being trapped in the lungs and hyperinflation of the lungs chronically.

The 4 major sub-categories of obstructive lung diseases are:

  1. Chronic bronchitis
  2. Emphysema
  3. Asthma
  4. Bronchiectasis

Note: These categories are not necessarily discreet diseases. They can (and often do) occur simultaneously with one another. The most common example of this is smoking related Chronic Obstructive Pulmonary Disease (COPD), in which patients often display characteristics of BOTH emphysema AND chronic bronchitis. All 4 types of obstructive lung disease have characteristic alterations to the pulmonary function tests:

  • Greatly decreased FEV1
  • Decreased or normal FVC
  • Decreased FEV1/FVC ratio
  • Increased Residual Volume (RV)
  • Increased Total Lung Capacity (TLC)
27
Q

With a “right shift” in the hemoglobin dissociation curve, does hemoglobin have a greater affinity or less affinity for oxygen? Does this shift facilitate loading of oxygen at the lungs or unloading of oxygen at the tissues?

A

When P50 > 26.7mmHg, the hemoglobin dissociation curve is said to exhibit a “right shift.” With a right shift, hemoglobin has less affinity for O2, which facilitates unloading of O2 in the tissues.

Right shift occurs with:

  • Increased temperature (ex: tissues with increased metabolic activity)
  • Increased [H+] (decreased pH)
  • Higher altitude
  • Increased [2,3-BPG] (aka 2,3-DPG)
  • CHRONIC anemia, which causes an increase in [2,3-BPG]

The factors that cause a right shift in the oxygen hemoglobin dissociation curve can be remembered with mnemonic: “CADETs face right”

  • CO2 (increased [CO2] )
  • Acidosis, Anemia
  • 2,3-DPG
  • Elevation
  • Temperature increase

MSAP 2015 (10 decks)

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