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Bichem > Hemo and myo > Flashcards

Hemo and myo Flashcards

1
Q

Heme proteins

A

-a group of specialized proteins that contain heme as a tightly bound prosthetic

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2
Q

Prosthetic group

A

coenzyme that is permanently associated with the enzyme or other protein and returned to its original form

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3
Q

Myoglobin and hemoglobin

A

heme is used to reversibly bind oxygen

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4
Q

Structure of heme

A
  • heme is most prevalent porphyrin in humans
  • uses iron held in the center of the heme molecule by bonds to the four mitrogens of the porphyrin ring
  • the heme iron can form two additional bonds (6 total)
  • (in heme and myo, one bond is with the R group of a histidine residue and one bond is to bind oxygen.
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5
Q

Myoglobin structure and function

A
  • in heart and skeletal muscle
  • oxygen reservoir
  • oxygen carrier that increases rate of transportation within muscle cell
  • single polypeptide
  • alpha helix stretches
  • -one histidine binds to iron and one histidine stabilizes binding of oxygen
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6
Q

Where is hemoglobin found and what is its function?

A

EXCLUSIVELY IN RED BLOOD CELLS

- transport oxygen from the lungs to the capillaries

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7
Q

Hemoglobin A structure

A
  • -major adult hemoglobin

- 4 polypeptide chains, two alpha chains, two beta chains, all connected by noncovalent interactions

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8
Q

Hemoglobin transportation

A
  • can transport 4 molecules of oxygen from lungs to peripheral tissues
  • can transport CO2 and H+ from the peripheral tissues back to the lungs
  • oxygen binding properties are regulated by interactions with allosteic effectors
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9
Q

Quaternary structure of hemoglobin

A
  • tetramer can be envisioned as two identical dimers (alpha-beta) and each dimer is held together by hydrophobic interactions.
  • dimers are attached by weak ionic and hydrogen bonds and the amount of polar bonding between the two dimers depends on whether or not oxygen is bound
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10
Q

forms of hemoglobin

A

T form(taut/tense): deoxygenated form of hemoglobin when no oxygen is bound and is the LOW OXYGEN AFFINITY FORM

R form(relaxed form): binding of oxygen to hemoglobin causes a break in some of the polar bonds between the dimers and is the HIGH OXYGEN AFFINITY FORM.

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11
Q

How many oxygen molecules can myoglobin and hemoglobin bind to?

A

Myoglobin can only bind to 1 oxygen

hemoglobin can bind to 4 oxygen

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12
Q

Degree of saturation with oxygen

A
  • y axis

- varies between 0%(all sites are empty) and 100%(all sites are full)

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13
Q

Partial pressure of oxygen

A
  • x axis
  • P50 is partial pressure of oxygen to achieve half saturation of the binding sites.
  • lower than P50 means high affinity
  • higher than P50 means low affinity
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14
Q

Myoglobin curve

A
  • hyperbolic shape
  • very low P50
  • very high oxygen affinity
  • designed to bind oxygen at low partial pressure in muscle and release in response to oxygen demand
  • high affinity in PO2 for peripheral tissues because it does not want to let go
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15
Q

Hemoglobin curve

A
  • sigmoidal shape
  • cooperative binding
  • steep slope in the range that accounts for peripheral tissues so that the hemoglobin is more likely to respond to small changes in pressure and release O there
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16
Q

Heme-Heme interactions

A
  • -binding of oxygen changes the structure of hemoglobin so that affinity increases for the others
  • allows hemoglobin to deliver oxygen o tissues in response to small changes in partial pressure.
  • interactions of dimers and subunits based on binding to oxygen
17
Q

Bohr effect

A
  • hemoglobin has less affinity for oxygen at lower pH.
  • shifts curve to the right
  • higher likelihood of complete unloading
18
Q

CO2 bohr effect

A
  • High levels of CO2 and lactic acid result in large amounts of carbonic acid
  • large pH gradient between muscles and lungs to increase efficiency of hemoglobin as oxygen transporter.
  • shifts graph to the right
19
Q

Mechanism of Bohr effect

A
  • Deoxygenated hemoglobin has a higher affinity for protons than oxygenated hemoglobin
  • protonated version has stronger ionic interactions
  • more stable T form
  • lower affinity for Oxygen
20
Q

2,3 BPG

A
  • only binds to deoxygenated hemoglobin
  • stabilizes T form
  • decreases affinity for oxygen
  • bind in pocket between beta globin chains in deoxyhemoglobin
  • positive amino acids bind to negative 23BPG
  • stabilize T form
  • when oxygen is bound, 23BPG is expelled
  • increased altitudes means more bpg and more efficient unloading
  • 23BPG is necessary for life to make sure affinity is not too high and O cant unload

-lost when blood is in storage

21
Q

CO2 binding effect

A
  • usually bicarbonate ion form
  • bound to N terminal amino group to form CARBAMINOHEMOGLOBIN
  • stabilizes T form
  • right shit in graph (less oxygen affinity)
  • released in lungs
22
Q

CO binding effect

A
  • hemoglobin has much higher affinity for CO than O
  • competes with O for spots
  • high affinity for oxygen, less slots for O, very little oxygen transport
  • shift graph to the LEFT
23
Q

Fetal hemoglobin

A
  • two alpha chains and two gamma chains
  • gamma chains lack positively charged amino acids so dont bind with 23 BPG
  • higher affinity for oxygen
  • able to absorb oxygen from mom over placenta
24
Q

Hemoglobin A1C

A
  • formed by HbA by glycolation
  • depends on concentration of glucose
  • diabetics will have higher levels of HA1C
25
Q

Sickle cell anemia characteristics

A
  • hemoglobin S
  • most common inherited blood disorder
  • symptoms not seen until fetal hemoglobin is replaced with hemoglobin S
  • increased susceptibility to infection
  • cells have shorter life span
  • glutamate is replaced by valine (more positive) so migrates slower under electrophoresis
26
Q

Sickle cell anemia mechanisms stuff

A
  • valine creates protrusion on the beta-globin that should fit into its site
  • in T form, hemoglobin polymerizes and stiffens to distort the cell
  • distorted cells interrupt the flow of blood and case anoxia
  • high altitude, decreased pH, 23BPG increases sickling
27
Q

HbSC

A
  • one copy of HbS and one copy of HbC.
  • variable symptoms
  • some sickling but less paint
  • HbC has mutation of LYS instead of GLU

Bichem (9 decks)

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