Chapter 7: Protein Function: Myoglobin and Hemoglobin, Muscle Contraction, and Antibodies Flashcards
Compare and contrast myoglobin and hemoglobins
similarities: bind to oxygen molecules by using prosthetic groups called heme groups.
differences: myoglobin has a single (monomeric) polypeptide, single heme group, more simple
hemoglobin is a tetramer consisting of 4 polypeptides, more complex, contains four heme groups. delivers oxygen to tissues throughout the body
myoglobin has how many a helices
small intracellular protein in vertebrate muscle with 8 helices
Describe heme group structure
Each heme group consists of an organic component called porphyrin and an inorganic component that consists of a single iron atom. The iron atom is located at the center of the organic component and is bound to four different nitrogen atoms
. This oxygen is brought to the cells by what two proteins and how?
myoglobin and hemoglobin. Both of these proteins have the ability to bind to oxygen molecules by using prosthetic groups called heme groups.
Myoglobin binds O2 to facilitate what
Oxygens diffusion
major role of myolglobin
its major physiological role is to facilitate oxygen diffusion in muscle also oxygen storage protein
heme group is responsible for what
the actual binding to the oxygen
which can bind more oxygen
hemoglobin cause of 4 subunits need 4 hemes hemes each give one oxygen
why is myoglobin oxygen binding curve hyperbolic
hyperbolic due to the high affinity myoglobin with oxygen.
p50 for myoglobin is?
2.8 torr
name another oxygen transport protein
hemocyanin
Hemocyanins, which are exclusively extracellular, in invertebrates, transport O 2 in mollusks and arthropods. e large multimeric proteins that differ in their primary through quaternary structures. However, their oxygen-binding sites are highly similar, consisting of a pair of copper atoms, each liganded by three His residues.
what kind of curve does hemoglobin form and why?
sigmoidal (s) curve because it has a lot smaller binding affinity to oxygen/cooperative interactions
what are hemoglobins 2 conformations
T-state (tense, lacks oxygen) deoxyhemoglobin and the R-state (relaxed, fully oxygenated) oxyhemoglobin
what are hemoglobins 2 conformations
goes from T to R with the addition of oxygen
T-state (tense, lacks oxygen) deoxyhemoglobin and the R-state (relaxed, fully oxygenated) oxyhemoglobin
name the equations used for hemoglobin
hill equation
hemoglobin has a p50 of?
26 torr
what kind of subunits does hemoglobin consist of?
2β 2tetramer (a dimer of α β protomers)
2 idenical ab dimers
definitions of saturation and partial pressure?
Saturatution-how much of protein is bound to oxygen
Partial pressure-concentraion of oxygen
how does myoglobin help facilitate diffusion
-quicker diffusion
The rate at which O 2 can diffuse from the capillaries to the tissues is limited by its low solubility in aqueous solution (∼10 −4 M in blood). Myoglobin increases the effective solubility of O 2 in muscle cells, acting as a kind of molecular bucket brigade to boost the O 2 diffusion rate.
The oxygen-storage function of myoglobin is probably significant only in?
The oxygen-storage function of myoglobin is probably significant only in aquatic mammals such as seals and whales, need it to dive deeper
Myoglobin’s Oxygen-Binding Curve Is ?
Hyperbolic
the mb equation describes its?
hyperbola
describe myoglobin’s hyperbola in terms of pO2,YO2 and O2
At low pO2, very little O 2 binds to myoglobin (Y O 2 is very small). As the pO 2 increases, more O2 binds to myoglobin. At very high pO2 , virtually all the O2 -binding sites are occupied and myoglobin is said to be saturated with O2.
K=?
P50
Myoglobin, a single polypeptide chain with one heme group and hence one oxygen-binding site, is a useful model for?
other binding proteins
Even proteins with multiple binding sites for the same small molecule, or ligand, may generate hyperbolic binding curves like myoglobin’s. A hyperbolic binding curve occurs when ligands interact independently with their binding sites.
Myoglobin is half-saturated with O 2(Y O2= 0.5) at an oxygen partial pressure (pO2) of ?
2.8 torr
Hemoglobin gives blood its?
color
Hemoglobin gives blood its? and where is it contained?
color
erythrocytes (RBC)
Idek
The α β protomers of hemoglobin are symmetrically related by a 2-fold rotation (i.e., a rotation of 180° brings the protomers into coincidence). In addition, hemoglobin’s structurally similar α and β subunits are related by an approximate 2-fold rotation (pseudosymmetry) whose axis is perpendicular to that of the exact 2-fold rotation.
what happens when oxygen binds to hemoglobin
alters the structure of the entire hemoglobin tetramer to form the 2 conformations
When oxygen binds to hemoglobin, the α1 – β 2 (and α2 – β 1 ) contacts shift, producing a change in quaternary structure.
what happens to iron during oxygen binding?
changes its position. so because of the electronegative character of oxygen when ditomic oxygen shown here actually
binds on to this heme group more
specifically onto the iron of that heme
group, it pulls away some of that
electron density from that heme group. it
pulls away some of that electron density
from that iron atom, and because some of
the electrons move away from that iron
atom it decreases the electron density
and the size of that iron atom, and now
because the iron atom is smaller it is
able to move into the
center of the plane of that
protoporphyrin
what causes cooperative behavior in hemoglobin?
In any binding system, a sigmoidal curve is diagnostic of a cooperative interaction between binding sites.This means that the binding of a ligand to one site affects the binding of additional ligands to the other sites. In the case of hemoglobin, O 2 binding to one subunit increases the O 2affinity of the remaining subunits.
differrence between deoxyhemoglobin and oxyhemoglobin
Deoxy -no heme groups are present, very constrained because few interactions
Oxy- when oxygen binds, causes interactions between surfac3es of polypeptide
Lifts restraints
s curve implies?
cooperative interactions
In the hills equations for hills constant n, what does it mean if n=1, n>1, and n<1
If n = 1, noncooperative.
If n > 1, the reaction is described as being positively cooperative,
if n < 1, the reaction is said to be negatively cooperative,
binding of oxygen to one submit increases or decreases the oxygen binding affinity ?
increases
this is positive cooperatively
binding of oxygen to one submit increases or decreases the oxygen binding affinity ?
increases
this is positive cooperatively
oxygen binding shifts the state from T to R and the Fe ion into where?
the porphyrin plane
which has a low affinity for oxygen T or R
T
in the Bohr effect the O2 affinity of hemoglobin increases with?
increasing pH/removing protons
shif of the binding curve to the left or right means what?
left=low oxygen affinity T state
right=high oxygen affinity R state
How are the protomer subunits held together in hemoglobin ?
by hydrophobic interactions, hydrogen bonding, and ion pairs (salt bridges) between oppositely charged amino acid side chains.
what is the Bohr effect
allosteric effects are hydrogen ions, CO2, and 2-3BPG that increase the amount of oxygen that is released by hemoglobin this is known as the BOHR effect which is when hyd ions and CO2 bind onto hemoglobin stabilizing its T state, decreasing affinity, shifting curve right
Decrease pH=increase or decrease of hydrogen ions
increase
3 allosteric effectors
BPG, CO2, Hydrogen Ions
how do hydrogen ions promote the release of oxygen in hemoglobin?
low pH allows the formation of ionic interactions that stabilize the T state of hemoglobin
how does carbon dioxide promote the release of oxygen in hemoglobin?
CO2 reacts with terminal amino groups to form negatively charged carbamate groups. The carbamate forms salt bridges that stabilize the T state.
CO2 and H+ are what kind of regulators of oxygen binding by hemoglobin?
heterotrophic
hemoglobins allosteric regulator? purpose? function?
2,3-bisphosphoglycerate (BPG)
determines the oxygen affinity of hemoglobin
It stabilizes the T state of hemoglobin and facilitates the release of oxygen by binding to a pocket in the hemoglobin tetramer that exists only when the hemoglobin is in the T state
The effects of BPG and CO2 on hemoglobin’s O2 dissociation curve.
Stripped hemoglobin (left) has higher O2 affinity than whole blood (red curve). Adding BPG or CO 2 or both to hemoglobin shifts the dissociation curve back to the right by decreasing oxygen affinity
fetal hemoglobin has low or high BPG affinity?
low, this means it has a higher affinity of oxygen than the adult/mother, supplies fetus with more oxygen from the maternal circulation
which does BPG bind tighter to? fetal or adult hb
adult
what is the fetal hemoglobins subunit composition
α 2γ 2, the b is replaced with a y
y is a variant of the b chain
Allosteric effects?
, in which the binding of a ligand at one site affects the binding of another ligand at another site, generally require interactions among subunits of oligomeric proteins.
* Two models that account for cooperative ligand binding: symmetry & sequential model)
an example of allosterism
oxygen binding to hemoglobin
what is allosterism
it describes the change in affinity for binding of a ligand or substrate that is caused by the binding of another ligand away from the active site
Not the same as cooperating
what can alter His structure and function?
mutations
what can alter His structure and function?
mutations
what Is the sickle cell trait that protects against malaria?
hemoglobin S
how many amino acid changes can cause sickle-cell anemia
just one
the smallest unit of the skeletal muscle is?
sarcomere
multiples sacromeres connect to form a ver ling fiber called
myofibril
myofibril consists of?
many adjacent sarcomeres
where are myofibrils located?
Myofibrils are placed inside the cytoplasm of the muscle cell also known as myocyte
sacromers are separated by ?
z lines/disks
Muscle cells contain many myofybrils that contain
sacromeres
what is the sliding filament model
its depicts the observation that during muscle contraction when interdigitated thick and thin filaments slide past each other the lengths of the I band and H zone decrease that results in the length reduction of the sarcomeres. the lengths of
the thick and thin filaments remain constant.
muscle becomes shorter, and because its total volume does not change, it also becomes thicker.
the main proteins found in muscle?
myosin and actin
thick filaments consist mainly of what protein
myosin
what chains do myosin consist of
2 heavy chains, 2 light chains
what must sarcomeres do for muscles to contract?
do the thick and thin filaments do the same
shorten
no, the filaments have to slide past each other towards the sarcomere center
how do the thick and thin filaments slide past each other
Myosin head is bound to ATP which lets it bind to the actin also known as cross bridging
Mysosin head performs a powerstroke which releases adp and phosphate aka filaments slide past each other towards the sarcomere center and a new atp binds the myosin head
Atp is needed to separate bind
what is cross bridging
Myosin head is bound to ATP which lets it bind to the actin also known as cross bridging
what is the powerstroke
filaments slide past each other towards the sarcomere center, adp is released and a new atp binds the myosin head
what occurs when the muscle is at rest/not contracting?
thin filaments containing actin have Tropomyosin and Troponin that act as regulatory proteins that block myosin binding sites on actin while at rest preventing contraction
what triggers the start of contraction?
a nerve impulse/neuron triggers the release of calcium and calcium ions bind to troponin. tropomyosin movies away from binding sites resulting in the exposure of myosin heads to bind again and contract.
calcium causes which protein to change its conformation and leave the binding sites?
tropomyosin
where is tropomyosin and troponin located
on thin filaments /actin
what triggers mucle contraction
calcium
actin forms what in nonmucle cells
microfilaments
two types of immune responses?
Cell and Humoral
What is humoral immunity?
most effective against bacterial infections and the extracellular phases of viral infections, is mediated by an enormously diverse collection of related proteins known as antibodies or immunoglobulin
what are antibodies produced by?
B lymphocytes or B cells
what is the immune system triggered by?
the presence of an antigen
what do immunoglobulins do in the presence of an antigen
B cells display immunoglobulins on their surfaces. If a B cell encounters an antigen that binds to its particular immunoglobulin, it engulfs the antigen–antibody complex, degrades it, and displays the antigen fragments on the cell surface.
what do immunoglobulins do in the presence of an antigen
B cells display immunoglobulins on their surfaces. If a B cell encounters an antigen that binds to its particular immunoglobulin, it engulfs the antigen–antibody complex, degrades it, and displays the antigen fragments on the cell surface.
what are memory cells
most B cells live only a few weeks unless stimulated by their corresponding antigen, a few long-lived memory B cells can recognize antigen several months or even many years later and can mount a more rapid and massive immune response (called a secondary response) than B cells that have not yet encountered their antigen
what are antibodies
highly specific proteins tproduced by plasma cells to respond to pathogenic antigens .
antibody function
to bind to its specific antigen and label it for destruction by the immune system
antibody structure
has four polypeptide subunits (2 large heavy chains and 2 small light chains) that connect via disulfide bond (noncovalent) to form a Y shaped structure
what regions do antibodies have
constant-determines the type immunoglobulin(5) or antibody, binds to the cell membranes of immune cells
variable- recognize the specific pattern (epiptope) on surface of antigen
is built to contain a specific sequence of amino acids that can bind to the specific antigen that it was built for. Contains the antigen-binding site
The region of the antigen that binds to the antigen-binding site is called ?
epitome or antigenic-dterminant
Antibody Diversity Results from ?
Gene Rearrangement and Mutation:
The immune system creates billions of different antibodies with a limited number of genes by rearranging DNA segments during B cell development, prior to antigen exposure. Mutation can also increase genetic variation in antibodies.
how is autoimmune disease caused.
Our immune system is tolerant to the healthy cells of ouy body and is not supposed to attack them. Can distiguish between helahyt and antigens
In certain cases immune system loses tolerance to healthy cells and cant differentiate between healthy and antigens. Wbc attack healthy and antigens this is known as autoimmune disease
Immunoglobulin folds in a what chain
light chain.
how many classes of immuniglobins
5
immunoglobulins differ in?
heavy chain
hypervariable loops are frequently mutated to allow diverse antigenic specificities to
be recognized
what to do when you need a small antibody in lab
attach it to a larger molecule
small antibody called a hapten
most antibodies recognize epitopes on large or small molecules
large
some compounds are too small to ellicit?
an immune response
some compounds are too small to ellicit?
an immune response
A hyperbolic binding curve occurs when?
ligands interact independently with their binding sites.
