Non-Enzymatic protein functions Flashcards
the 3 principal types of protein filaments in the cytoskeleton arragned by increasing size are….
- microfilaments
- intermediate filaments
- microtubules
which cell protein structure responsible for cellular motility and maintaining the cell’s structure?
Actin microfilaments
note: since microfilaments are responsible for cell structure, they are rigid
individual actin monomers are referred to as
G-actin
think: “G”lobular shape
During polymerization, G-actin units are strung together like beads on a necklace to form the polymer _____
F-actin
two strands of F-actijn form a microfilament
the act of an actin filament simultaneously growing on one end while shrinking at the other; process of rapid growth and assembly
treadmilling
any process in which relatively small molecules, called monomers, combine chemically to produce a very large chainlike or network molecule, called a polymer
polymerization
True or False
actin polymerization requires ATP
True
actin polymerizes when ATP-bound actin selectively adds to the plus (+) end of an ADP-actin cap at the shrinking minus (-) end.
____ are composed of various forms of protein subunits
intermediate filaments
____ are characterized by
* alpha helices, making them have a corkscrew structure
* flexible; can be stretched
* typically found in cytoplasm between nucleus and plasma membrane
* functions include structural support and cell adhesion to neighboring cells
intermediate filaments
name a common intermediate filament (that you will need to know for the MCAT!)
Keratin
makes up hair and nails
____ is a protein filament that has functions of
* movement of chromosomes during cell division
* intracellular transport
* neutrophil & amoeboid mobility
* cillia and flagella formation
microtubules
microtubule formation is initiated and organized in ____
microtubule organizing centers MTOCs
common MTOCs include the centrosome and the basal bodies found in the cilia and flagella
alpha and beta tubulin dimers are the building bloacks of ______
microtubules
alpha and beta tubulin dimers polymerize end to end in protofilaments in GTP-dependent processes
A filament of polymerized tubulin in a cell, which becomes part of a microtubule
protofilaments
13 protofilaments make a microtubule
the minimum concentration that dimers must be present at for polymerization to occur to form microtubules
critical concentration
kinesins, dyneins, and myosins are all ____ proteins
motor proteins
Motor proteins are proteins that help the cell move or that help move certain components (proteins, waste, nutrients, etc.) within the cell.
____ are motor proteins that travel along microtubules to transport cellular cargo. They also move toward the positive end of a microtubule, which faces the periphery of the cell (anterograde transport)
kinesins
movement away from the cell body; with kinesins do this by frequently involving the transport of membrane components and proteins bound for the plasma membrane or other locations at the cell periphery
anterograde transport
a protein made up of 4 distinct subunits, I.e kinesins
heterotetramers
motor proteins that carry cargo and walk towards the minus end of a microtubule, which is usually toward the center of the cell (retrograde transport)
dyneins
the two types of dyneins are:
axonemal and cytoplasmic
______ are dyneins only found in cells with cilia or flagella and help generate the sliding motion between micro tubules that is necessary for these structures to move
Axonemal dyneins
_____ dyneins transport cargo needed to carry out regular cell functions I.e components of organelles and vesicles, and helping position their cargo within the cytoplasm
cytoplasmic dyneins
True or False
kinases, dyeins, ATPases
True
a group of enzymes that catalyze the hydrolysis of a phosphate bond in adenosine triphosphate (ATP) to form adenosine diphosphate (ADP).
ATPase
____ protein filaments play a central role in muscle contraction
Myosin
think: “myo” means “muscle”!
how do myosins move during muscle contractions?
the head domains bind the actin of microfilaments and hydrolyze ATP to generate force and induce te movemment of the protien along filaments, towards the barbed (+) end. During skeletal muscle contractions, myosin II moleculees create a force by a power stroke mechanism that uses energy released by ATP hydrolysis
occurs when myosin is tightly bound to actin. When inorganic phosphate is released from mysin following ATP hydrolysis, a conformational change occurs wherein actin is pulled towards myosin. The actin will remain attached until the subsequent binding of an ATP molecule triggers its release
power stroke
cell adhesion molecules are classified into 3 categories…:
- selectins
- cadherins
- integrins
cell adhesion molecules are abbreviated as
CAMs
CAMs that mediate the inflammatory response, found in immune cells, platelets, and endothelial cells lining blood vessels
selectins
SELECTins SELECT the inflammatory/immune response
they slow down leukocytes and neutrophils during inflammatory response, they WBCs will stick to the selectins on their way to the infected area
calcium-depdendent CAMs involved in early stages of growth and development, and can bind to microfilaments of the cell’s cytoplasm.
cadherins
which CAM are mostly located in the membrane spanning region of the cell, and form adherens junctions that help link cell stick to each other within tissues?
Cadherins
CAdherins depend on CAlcium
large family of transmembrane proteins that act as both adhesion and signaling molecules
integrins
INTEGRins INTEGRate two functions
Name the three types of cell junctions you should know for the MCAT
- anchoring junctions
- gap junctions
- tight junctions
connect cytoskeletal components of the cell with the other cells and/or the extracellular matrix, contributing to the overall stability of tissues
anchoring junction
type of anchoring junction in which cadherin connects intermediate filaments to other cells
desmosomes
type of anchoring junction in which integrins connnect the intermediate filaments of the cells to the extracellular matrix
hemidesmosomes
cell junctions that are linked closely to one another, preventing solutes from moving freely from one tissue into another; found in epithelial cells
tight junctions
ex: they are in the blood-brain barrier, where epithelial cells in blood vessels form tight junctions that allow close regulation of substances that leave and enter the CNS
cell junctions that allow the exchange of ions, second messengers, and small metabolites between adjacent cells, formed by connexin proteins
gap junctions
proteins with attached carbohydrate components
glycoproteins
think: GLYCO = sugar = carbs
glycoproteins produced by B cells of the adaptive immune system, and belong to the immunoglobulin super family of proteins.
antibodies
Antibodies work by binding antigens
small parts of foreign molecules that the immune system has flagged as a potential threat and opted to destroy
antigens
when the body misidentifies part of itself as an antigen and generates antibodies against that element
autoimmune response
antibody isotype present in mucosal areas (i.e the gut, respiratory tract, saliva, tears, breast milk, and urogenital tract) that helps prevent colonization by pathogens
IgA
dimer
antibody isotype that primarily acts as an antigen receptor on B cells that have not been exposed to antigens. Involved in the activation of mast cells and basophils
IgD
Monomer
antibody isotype involved in allergies and anti-parasitic responses. Binds to allergens, causing histamine release from activated mast cells and basophils
IgE
Monomer
antibody isotype that provides most of the humoral immune response. It is the only antibody type capable of crossing the placeenta and conferring passive immuninity to a developing fetus
IgG
monomer
antibody isotype responsible for mounting an immune response and eliminating pathogens in the early stages of the humoral response, before IgG levels increase. Expressed on surface of B cells as a monomer and is secreted by plasma cells as a pentamer
IgM
the process where an activated B cell changes its antibody production from IgM to either IgA, IgG, or IgE depending on the functional requirements
class swithcing
aka isotope switching
what structural changes must occur for **class switching **to happen?
B cells modify the constant domain of an antibody’s heavy chain. The antibody retains its hypervariable region, so its antigen-binding site remains intact, but it gets repurposed for a different antibody class. Thus, the antibody can still bind to its same antigen, but it can accomplish new tasks for the immune system
the three major functional signaling molecules are:
- hormones
- cytokines
- neurotransmitters
signaling molecules of the immune system
cytokines
include ion channel-linked, enzyme-linked, and G-protein coupled receptors
membrane receptor
intracellular recepters are activated by lipid-soluble signals (e.g., steroid hormones) that cross the plasma membrane. Once activated, most function as transcription factors to control gene expression for numerous biological processes
nuclear receptor
ion-channel linked receptors are also known as
ligand-gated ion channels
cell membrane bound receptors that act through synaptic signaling on electrically excitable cells. Undergo conformational changes when a ligand binds to them, allowing the transmembrane pore to open, allowing the passage of a specific molecule
ion-channel linked receptors
ligands to which the receptor binds can be neurotransmitters and peptide hormones. The molecules that pass through are often ions i.e Na or K+
are either enzymes themselves or directly associated with enzymes that they activate. Majority are protein kinases or are associated with them. Common examples include receptor tyrosine kinases
enzyme-linked receptor
high-affinity cell surface receptors for many polypeptide growth factors and hormones. They are key regulators of normal cellular processes, while dysfunction is associated in the progression of many types of cancers
receptor tyrosine kinases
pg. 68 biochem
link
cascades of protein kinases which are activated by genotoxic stress and growth factors
mitogen-activated protein kinase pathway
p.69 biochem
receptors with transmembrane domains and experience conformational changes after binding with a ligand. They transfer extracellular signals across the plasma membrane to intracellular effectors via G proteins. Used by cells to convert extracellular signals into intracellular responses, including responses to hormones, neurotransmitters, as well as responses to vision, olfaction and taste signals
G-coupled protein receptors (GPCRs)
involved in many secondary messaging pathways
heterotrimeric (composed of α, β, and ɣ subunits) specialized proteins with the ability to bind (GTP) and (GDP). They are unactive when bound to GDP but are activated by binding to GTP.
G-proteins
Describe how GCPR signaling works
GPCR signaling is initiated when a ligand binds to the extracellular surface of the GPCR. This results in a conformational change in the GPCR causing the activation of the Gα subunit. The activated Gα exchanges bound GDP with GTP, resulting in the disassociation of the Gα subunit from the Gβγ dimer.
Two examples of secondary pathways that the MCAT expects you to know are:
- cAMP dependent pathway
- inositol triphosphate (IP3) pathway
a secondary messenger that activates certain ion channels and the enzyme protein kinase A (PKA) which affects cellular components of gene trancription and metabolism
cAMP
a secondary messeneger whose main functions are to mobilize Ca2+ from storage organelles and to regulate cell proliferation and other cellular reactions that require free calcium
IP3
describe IP3 signaling
PIP2 phosphilipid on cell membrane activated –> produces IP3 and DAG. –> IP3 diffuses through cell –> release of intracellular calcium triggered –> protein kinase C (PKC) activated –> cellular response
class of intracellular proteins that are responsible for sensing steroid and thyroid hormones, and certian other lipid-soluble signaling molecules. Main function is to afffect gene transcription
nuclear receptors
the molecules that bind to and activate nuclear receptors are ____philic
lipophilic
peptides, proteins, and other hydrophobic signaling moleucles must interact with the cell via ____
cell-membrane bound receptors
Name the macromolecule
____ can diffuse through the plasma embrane and move into the cell to interact with intracellular nuclear receptors
lipids
describe the functions of the two primary domains of a nuclear receptor
the ligand binding domain binds with the signaling molecule, and the DNA-binding domain has two “zinc finger” elements that bind to specific DNA sequences known as hormone response elements (HREs)
type 1 nuclear receptors are found in the ____ , where they bind to ligands before being translocated into the nucleus to exert their effects
cytoplasm
name the cell structure (it’s a repeat)
type 2 nuclear receptors are in the ____, so the hormne must enter the ____ to bind with the receptor to modify DNA transcription
nucleus
once a nuclear receptor binds an HRE sequence in DNA, it recruits other proteins known as _____
transcription regulators
proteins that facilitate or inhibit transcription via a range of mechanisms i.e chromatin remodeling
transcription coregulators
