Biochem exam 3

How are liposomes used in drug delivery?

Carriers in drug delivery (COVID mRNA vaccine packaged into liposomes)

What type of molecules can easily cross the membrane?

small, non-polar molecules (Gases like O2)

What travels faster through the membrane, small polar molecules (H2O, urea) or larger non-polar molecules (Trp)?

Small polar molecules! Larger non-polar molecules are slow due to size

What molecules have difficulty crossing the membrane?

Ions and charged molecules

How do polar molecules and ions cross the membrane?

Membrane proteins

Different cells have different % of proteins (20-75)

How can you infer what biochemistry is occurring inside of the cell?

The types of membrane proteins

The expression of membrane transporters

What is an example of a cell type with relatively low membrane protein content?

Schwann cells

Schwann cell membrane structure

lipid rich (serves as an insulator/fast transmission)

Low protein = flexibility (allows wrapping on the axon)

What is Multiple sclerosis?

an example of a demyelination disease, impairing myelin assembly or damaging existing myelin.

Integral membrane proteins

Embedded in the hydrocarbon membrane

Peripheral membrane proteins

Bound to the polar heads or exposed surfaces of an integral membrane protein

sometimes attached by hydrophobic moiety inserted in the membrane

Example of integral protein

Porin

Outside surface is hydrophobic and interacts with membrane interior

Inside surface is polar as it faces water.

Example of peripheral membrane protein

Prostaglandin H2 Synthase-1

How is Prostaglandin H2 Synthase-1 attached to the membrane

Mostly hydrophilic molecule has a small hydrophobic side chain that is embedded in the membrane

What does Prostaglandin H2 Synthase-1 do

Injury → Arachidonate → Goes through Cyclooxygenase → Prostaglandin G2 → Goes through peroxidase → Prostaglandin H2 → starts inflammation

What is the significance of the hydrophobic channel of Prostaglandin H2 Synthase 1

The cyclooxygenase (COX) activity depends on the channel to connect the active site to the membrane interior.

How does Aspirin inhibit COX activity?

By transferring an acetyl group to a serine residue in the hydrophobic channel, obstructing it.

Where would the hydrophobic amino acids of an integral protein reside?

Inside of the transmembrane domain (The part that passes through the phospholipid bilayer)

Do Prokaryotes or Eukaryotes contain compartments bound by internal membranes?

Eukaryotes

What is receptor-mediated endocytosis?

Cells acquire molecules from their environment by separating and fusing parts of the membrane (makes vesticles)

What is exocytosis?

Fusion of internal membranes with plasma membrane to allow the release of molecules such as neurotransmitters

What does Clathrin do?

Helps internalize receptors bound to their cargo (used in endocytosis, coats vesicles)

What are the 4 ways molecules can pass through the membrane?

Diffusion, Facilitated diffusion, passive transport, Active transport

What are the 3 classes of pumps?

ATP-driven pumps, carriers, and channels

How do hydrophobic/lipophilic molecules pass through the membrane?

Diffusion, down their concentration gradient (don’t need proteins)

How do polar/ charged molecules pass through the membrane?

Passive transport of facilitated diffusion down their concentration gradient.

What is Active transport

Moving a molecule across the membrane against its concentration gradient

How do pumps pump molecules across the membrane

ATP hydrolysis

What is an example of a membrane pump?

Na+-K+ pump (ATPase) through Active transport to keep membrane potential

How much of the ATP we produce is expended by Na/K pumps (cells and nerve cells)

30%

up to 70% for nerve cells

What are the two conformations of a pump?

Ion binding site facing into the cell

Ion binding site facing out of the cell

Why is Digitalis purpurea useful/dangerous? (foxglove)

It has cardiotonic steroids that inhibit Na/K ATPase dephosphorylation

Can be used to treat congestive heart failure

What are two examples of cardiotonic steroids?

Digitoxigenin and Ouabain

What does Digitoxigenin do?

Decrease in Na+ gradient = slower removal of Ca+ from cell (increased Ca+ in cell) = enhanced contractile ability of the heart

What is Multidrug-resistance protein?

ATP-dependent pump that extrudes small molecules out of the cell.

What family of transporters in Multidrug-resistance protein from?

ABC transporters

What is the common domain of ABC transporters?

APT-binding cassette (ABC)

What is an example of an ABC protein?

Multidrug resistance protein in bacteria

ABC transporter mechanism

What do secondary transporters / cotransporters do?

They use energy of one gradient to power the formation of another

What are the 3 types of transporters?

Symporters, Antiporters, Uniporters

Symporters

Transport molecule B against its concentration gradient by coupling its movement with molecule A down its concentration gradient

Both molecules move the same direction

What is an example of a Symporter?

Sodium glucose symport

Antiporters

Molecule B exits while molecule A enters

What is an example of an Antiporter

Sodium calcium exchanger

Uniporters

Transports a single molecule either direction

what is an example of an Uniporter

glucose transporter

What do Ion channels do?

Allow rapid movement of ions across membranes down their concentration grandient

What does the potassium channel do?

Ion channel selectively and rapidly transports K+ across the membrane

Bigger ions = too big

Smaller ions = can’t interact

What does epinephrine bind to? What does it do?

Beta-Adrenergic receptor

Energy-store mobilization

What does Insulin bind to? What does it do?

Insulin receptor

Increased glucose uptake

What does Epidermal growth factor bind to? What does it do?

EGF receptor

Expression of growth-promoting genes

Signal cascade common components

Stimuli

Release primary message

Relay message through second messenger

Activate effector

Terminate signal cascade

Is the signal of second messenger equal to initial signal?

Second messenger is amplified

What are common second messengers?

cAMP, cGMP, Calcium ion, Inositol 1,4,5-triphosphate (IP3)

What type of receptor is a GPCR? (beta-adrenergic receptor)

Seven-transmembrane-helix

How does the binding of a ligand affect b-adrenergic receptor

It induces structural changes inside of the cell and initiate fight or flight response

How does epinephrine signal transduction cause changes in a cell?

Activates protein kinase A though G-protein pathway

What does epinephrine cause in liver cells?

Epinephrine Promotes glucose release from liver cells

What changes does epinephrine cause in muscle cells?

Promotes calcium release within muscle cells

What is an example of a common Ca+ sensor

Calmodulin

How many binding sites does Calmodulin have

4, called EF hands

What does the Ca2+ calmodulin complex activate

Variety of biochemical targets

Plasma membrane Ca+ ATPase

How are Kinase transduction pathways turned off?

Protein phosphatase removes phosphates through dephosphorylation

How are G-protein transduction pathways turned off?

GTPase inactivates after the target has been activated

How are cAMP transduction pathways turned off?

Phosphodiesterases break down cAMP into AMP

What type of receptors do hormones such as insulin bind to?

Receptor Tyrosine Kinase

What happens after the ligand binds to a receptor tyrosine kinase

Sometimes dimers are formed

Are insulin receptors dimers?

Yes, even in the absence of insulin

What is the structure of the insulin receptor hormone binding site?

two alpha subinits outside the sell

What do alpha subunits activate?

2 beta subunits, activate tyrosine kinase to phosphorylate.

Simple insulin→glucose pathway

Insulin in insulin receptor → cross-phosphorylation → activates 2 kinase domains → phosphorylates IRSs to activate IRSs → IRS1 activates PI3 kinase → PIP2 becomes PIP3 → PIP3 activates PDK1 → PDK1 phosphorylates (activates) Akt → Akt stimulates GLUT4 allowing glucose to enter

What does epidermal growth factor activate?

Ras

Epidermal growth factor (EGF) → Ras pathway

EGF binds to EGFR → promotes dimerization/cross-phosphorylation of EGFR → Phosphotyrosine of EGFR attach to SH2+Grb2 → forms complex with Sos → promotes exchange of GDP to GTP → activates Ras

What does Ras do?

Promotes cell division

How does Ras promote cell division?

MAP kinase cascade to activate AP1 (start with 3 kinase, and cut one off each time)

How is EGF terminated

Specific serine/threonine phosphatases

Tyrosine phosphatases

What does uncontrolled activity of Ras/MAP kinase lead to?

Cancer

What is Cetuximab?

Used to treat colorectal cancer

Competitive inhibitor of EGFR (growth factor receptor)

What are mutated genes that can cause cancer called?

Oncogenes

Tumor suppressors

What is an example of an oncogene?

Ras = protooncogene

Mutated Ras = oncogene

What is an example of a tumor supressor gene?

Mutated phosphates that terminate EGF

BRCA1

What is Cholera toxin

secreated by intestinal bacterium vibrio cholerae

Modifies the G_as protein = constantly active

What happens when g protein is constantly active

Continuous production of kinase A = altered ion channels and excessive loss of NaCl & water = diarrhea

How does nitric oxide impact cell signaling?

Nitric oxide diffuses across the membrane and widens blood vessels

What does NO activate?

Protein kinase G → lowered Ca+ levels → smooth muscle relaxation

What are fat-soluble vitamins?

Vitamin K, Vitamin A, Vitamin E, 1,25-Dihydreoxyvitamin D3

(be able to recognize, not draw)

Vitamin K

(be able to recognize, not draw)

Vitamin A

Be able to recognize, not draw

Vitamin E

Be able to recognize, not draw

1,25-Dihydreoxyvitamin D3

Why do metabolic pathways have to be regulated?

To maintain homeostasis

How to maintain homeostasis?

Constant monitoring of nutrient levels

Adjusting metabolism to meet cell needs

What are the 3 regulatory strategies of homeostasis

Controlling the amounts of enzymes

Controlling catalytic activity

Controlling the accessibility of substrates

How is the amount of enzyme controlled?

rate of synthesis (long term)

rate of degradation (long term)

How is the catalytic activity of an enzyme controlled?

Allosteric regulation (fast)

Covalent modification (phosphorylation, methylation, ect)

How do hormones coordinate metabolic relations between tissues?

Regulating the reversible modification of key enzymes

Can synthesis and degradation of a reaction occur in different locations? example

Yes

Fatty acid oxidation = in mitochondrial matirx

Fatty acid synthesis = in cytoplasm

What is the function of vitamin A?

Supports vision, growth, reproduction

What happens with vitamin A deficiency?

Night blindness