Cell Physiology

Question 1

rough endoplasmic reticulum

Answer 1

Rough endoplasmic reticulum contains ribosomes on its surface - ribosomes organelles for synthesizing proteins - as amino acid sequence is put together, Chemicals, such as carbohydrates or sugars, are added, then the endoplasmic reticulum either transports the completed proteins, called secretory proteins, to areas of the cell where they are needed, or they are sent to the Golgi apparatus for further processing and modification.

Question 2

smooth endoplasmic reticulum

Answer 2

Enzymes of the smooth ER are vital to the synthesis of lipids, including oils, phospholipids, and steroids.

Question 3

Golgi apparatus

Answer 3

• protein modification
• The section of the Golgi apparatus that receives the vesicles from the ER is known as the cis face, and is usually near the ER. The opposite end of the Golgi apparatus is called the trans face, this is where the modified compounds leave. The trans face is usually facing the plasma membrane, which is where most of the substances the Golgi apparatus modifies are sent.
• Golgi puts lipids and proteins together and/or adds carbohydrate groups to the molecules made by the ER.

Question 4

Vesicles

Answer 4

small membrane-enclosed transport units that can transfer molecules between different compartments.

Question 5

Endomembrane system

Answer 5

endomembrane system include: the nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes

• making secretory products
• responsible for adding to and renewing the plasma membrane

Question 6

steps involved in synthesizing a glycoprotein for secretion starting with a gene in the nucleus

Step 1

Answer 6

1). The cell’s nucleus contains DNA which is organized into genes. A gene is a sequence of DNA that codes for a protein. This is where the phrase “genetic code” comes from. DNA is made of a sequence of nucleotides; there is information in that sequence of 4 bases. The sequence of DNA nucleotides can be transcribed into a sequence of mRNA nucleotides and then that sequence can be translated into a sequence of amino acids in a protein.

Question 7

steps involved in synthesizing a glycoprotein for secretion starting with a gene in the nucleus

Step 2

Answer 7

A unifying principle is that the structure of a protein then determines its function. What kinds of proteins can be made? : Structural proteins like actin, enzymes like glycolytic enzymes, proteins that regulate gene expression like transcription factors and secretory products like protein hormones and digestive enzymes

Question 8

steps involved in synthesizing a glycoprotein for secretion starting with a gene in the nucleus

Step 3

Answer 8

If the secretory product is a protein - a gene in nucleus is transcribed to an RNA molecule - messenger RNA molecule diffuses out of nucleus to cytoplasm where protein synthesizing organelles and enzymes are located. Rough endoplasmic reticulum contains ribosomes on its surface - ribosomes organelles for synthesizing proteins - as amino acid sequence is put together, peptide feeds into the rER and the finished product is packaged into a vesicle. Molecular chaperones guide the folding of many proteins and prevent newly synthesized proteins from forming inappropriate protein aggregates.

Question 9

Endoplasmic reticulum

Answer 9

membranous synthesis and transport organelle that is an extension of the nuclear envelope.

Question 10

steps involved in synthesizing a glycoprotein for secretion starting with a gene in the nucleus

Step 4

Answer 10

If the secretory product is a lipid then enzymes within the smooth endoplasmic reticulum (sER) synthesize the lipid molecules. Depending on the size of the lipids, they may be incorporated into vesicles or as in the case of steroid, may simply diffuse out of the cell.

Question 11

steps involved in synthesizing a glycoprotein for secretion starting with a gene in the nucleus

Step 5

Answer 11

Vesicles from rER and sER are transported to Golgi apparatus. Golgi puts lipids and proteins together and/or adds carbohydrate groups to the molecules made by the ER. Synthesized molecules are repackaged by Golgi and sorted according to destination. Vesicles are released at the appropriate time in response to the appropriate signal.

Question 12

steps involved in synthesizing a glycoprotein for secretion starting with a gene in the nucleus

Step 6

Answer 12

With the appropriate signal, contents of vesicles are released by exocytosis. An increase in intracellular Ca is signal. Lipid membrane of vesicle fuses with lipid membrane of cell membrane and the contents of vesicle released into extracellular fluid.

Question 13

What are the consequences of a change in the sequence of nucleotides within in a gene?

Answer 13

A mutation in the gene sequence can lead to the translation of a defective protein. The reduction or loss of protein function can result in disease. For example, Spinal muscular atrophy results from a mutation in the smn1 gene coding for the Survival of Motor Neuron (SMN) protein. With limited functioning of SMN, motor neurons in the anterior horn degenerate.

Question 14

What is the function HSP/Chaperones?

Answer 14

assist the covalent folding or unfolding and the assembly or disassembly of other macromolecular structures.

Found in ER

Question 15

Why would a cell make a chaperone protein?

Answer 15

Many chaperones are heat shock proteins, that is, proteins expressed in response to elevated temperatures or other cellular stresses.[6] The reason for this behavior is that protein folding is severely affected by heat and, therefore, some chaperones act to prevent or correct damage caused by misfolding. Other chaperones are involved in folding newly made proteins as they are extruded from the ribosome

Question 16

When chaperone proteins have a mutation

Answer 16

At least 5 human diseases have been identified to be causes by a mutation in a chaperone protein. All are characterized by a loss of a protein structure/function and protein aggregates. Affected individuals have multiple problems such as polydactyly, movement disorders, neuromuscular disorders, retinal disorders, genital malformations etc.

Question 17

How does the membrane system process harmful or worn out cellular material?

Answer 17

Old cellular material can be labeled with polymerized ubiquitin (chaperone protein) guided into a proteasome (a protein degrading complex) and hydrolyzed. The products of degradation are reused by the cell or released into the ECF.

Question 18

Possible consequences to cells if lysosomes are not functioning properly (hint - what are storage disorders?).

Answer 18

The inability of lysosomes to process waste results in storage diseases such as Gaucher’s disease (mutation in enzyme that breaks down cerebrosides, membrane glycolipids) and Tay Sach’s disease (a mutation in gangliosides, neural glycolipids). Both these diseases are enzyme mutations and are Autosomal recessive.

Question 19

Why is calcium regulation so important to cellular homeostasis?

Answer 19

Calcium is a very important signaling ion and therefore the cell must invest a lot of energy into keep intracellular calcium low (nanomolar concentrations). There are calcium ATPases which directly use ATP to pump out calcium and some cells contain Na/Calcium exchangers (which use ATP indirectly. Calcium ATPases can be in the plasma membrane or endoplasmic (sarcoplasmic) reticulum.

Question 20

What affect does hypoxia have on intracellular calcium?

Answer 20

Hypoxia tends to disrupt calcium metabolism given that cells need ATP to sequester Ca in the SR or outside the cells.

Question 21

Glycolysis

Answer 21

a molecule of glucose is destabilized via phosphorylation and then through a series of steps, glucose is broken into two pyruvic acid molecules to net two ATP molecules. Glycolytic enzymes are located in the cytoplasm and produced ATP quickly without O2 (anaerobic metabolism).

Question 22

Kreb’s cycle

Answer 22

Pyruvic acid enters the mitochondria. organic molecules are moved through the series of reactions, covalent bonds are broken. As carbons are removed, carbon is oxidized to CO2 is produced. Some of the energy released from the broken bond is used to reduce NAD+ and FAD to NADH and FADH2 and some of the energy is given off as heat (head production with metabolism is a given). NADH and FADH2 are energy carriers that interact with electron transport chain within membrane cristae where the cytochromes are contained.

Question 23

Oxidative phosphorylation

Answer 23

NADH and FADH2 donate energy to the ETC in the form of high energy electrons. As electrons shuttle through the ETC, H+ are moved to the space between the two mitochondrial membranes. The resulting H+ gradient drives an ATP synthase pump. At the end of the ETC, the electrons are accepted by O2, and O2 is converted to H20.

Question 24

How do mitochondria protect the cell from oxidative stress (reactive oxygen species)?

Answer 24

Free radicals can be neutralized by peroxisomes. Free radicals can produce a substance called peroxide (H2O2) which can lead to the production of other free radicals. Peroxisomes contain perioxidase (catalase) which breaks down H2O2 into water and O2, and hence neutralizes free radical cascades.
MITOCHONDRIA
a. O2 can react with other O2 molecules to form free radicals like superoxide (ROS - reactive oxygen species) but superoxide dismutase in mitochondria neutralizes free radicals

Question 25

What happens to ATP production without O2?

Answer 25

Without O2, the electrons jam up the in chain and ATP synthesis stops. The cells use a fermentation reaction to make ATP anaerobically. The energy in NADH is transferred to pyruvate to make NAD+ and lactate. NAD+ can keep glycolysis going in the absence of O2 and lactate can be used as an energy source when O2 returns.

Question 26

Endocytosis

Answer 26

Because membranes are flexible, cells are able to surround incoming material with membrane and ingest it through a process called endocytosis. Subtypes of endocytosis are pinocytosis (cell drinking) and phagocytosis (cell eating).
-receptor mediated endocytosis is triggered when a ligand binds to receptor within protein laden pits that facilitate intake of the material. The protein in the pits is called clathrin. The clathrins are on the intracellular face of the pits and facilitate the endocytosis process.

Question 27

Clinical application for endocytosis

Answer 27

HIV enters neurons and T helper cells via receptor mediated endocytosis

Question 28

Clinical application for endocytosis

Answer 28

HIV enters neurons and T helper cells via receptor mediated endocytosis

Question 29

Cytoskeleton

Answer 29

The cytoskeleton attaches to vesicles and transports them within cell, moves the cell membrane to form pseudopodia which surround external material and brings the endosome inside the cells. The cytoskeleton is important for moving chromosomes during cell division. The cytoskeleton is very important for neuronal function and axon strength, given a neuron axon could be a meter long.

Question 30

Clinical application for cytoskeleton

Answer 30

Inhibition of the cytoskeleton inhibits the growth of cancer.

Question 31

Fluid mosaic model

Answer 31

• Plasma membrane
• Basically, proteins float around in a bilayer sea of phospholipid with varying degrees of lateral motion. The components do not need covalent bonds to say together. Instead they take advantage of hydrophobic/hydrophilic interactions to maintain a stable structure. The structure is stable because it resides in its lowest energy state. The hydrophobic elements cluster together and the hydrophilic elements touching the aqueous compartments such that hydrogen bonding is maximized.

Question 32

Major component of plasma membrane

Answer 32

amphipathic phospholipids

• Hydrophobic tails point to the inner portion of the bilayer and hydrophilic heads associate with the aqueous compartments.
• Cholesterol interdigitates between the phospholipids to change the strength and flexibility of the membrane.
• Cholesterol is a hydrophobic molecule but it does have a hydroxyl group that helps it orient in the bilayer so technically you could call it amphipathic. There are lipids with sugar groups; again the tail points inward and the carbohydrate faces the ECF

Question 33

Integral proteins

Answer 33

• Plasma membrane
• amphipathic because the lipid soluble amino acid groups touch the bilayer and the water soluble amino acid groups touch the aqueous compartments
• Other proteins are peripheral to the membrane and associate only with the polar parts of the phospholipids or integral proteins

Question 34

What is a second messenger system?

Answer 34

permit a chemical signal on the outside of the cell to activate a cascade of processes inside the cell without the first messenger having to enter the cell.

Question 35

What two enzymes function to increase or decrease cAMP levels?

Answer 35

Protein Kinase A increase cAMP and Phosphodiesterase decreases cAMP

Question 36

adenylate cyclase system

Answer 36

When a ligand binds to its specific receptor a heterotrimeric G protein undergoes a separation to regulate a membrane enzyme, adenylyl cyclase. Adenyl cyclase converts ATP into cAMP. cAMP is a second messenger that activates Protein Kinase A (PKA). PKA phosphorylates proteins to either activate or inactivate intracellular proteins providing a means of intracellular enzyme regulation. A second membrane enzyme, phosphodiesterase, is required to turn the system off - phosphodiesterase breaks down cAMP

Question 37

Selective permeability

Answer 37

Plasma membrane allows some substances to cross more easily than others. The membrane must regulate what substances can enter and exit cell. If a substance can cross membrane that molecule is permeant or the membrane is permeable to it. Not all substances can cross, hence selective permeability.

Furthermore, permeability is relative - some substances more permeant than others.

Question 38

Determinants of permeability

Answer 38

lipid solubility, size and charge

Question 39

Lipid soluble ions/molecules

Answer 39

• O2, CO2, nitrous oxide, free fatty acids (FFA), small alcohols (R-OH), chloroform, ether, general anesthetics)
• can pass through membrane

Question 40

4 types of Ion channels

Answer 40

• Voltage-gated channels that are gated by changes in membrane potential
• Ligand-gated channels that are regulated by ligands, i.e., chemicals that bind to it
• Mechanically gated channels that are ion channels whose pore responds to mechanical stimuli like stretch
• Leak channels

Question 41

Diffusion

Answer 41

passive process by which molecules move randomly along a concentration gradient

Question 42

Factors that affect diffusion

Answer 42

temperature, concentration and electrical differences. particle size, surface area of membrane, diffusion distance, medium (gas versus liquid), membrane characteristics

Question 43

What determines the direction of osmosis?

Answer 43

diffusion of H20 through semipermeable membrane along its concentration gradient - So osmosis is determined by water difference btwn 2 compartments

Question 44

Tonicity

Answer 44

concentration of impermeant solute or fixed particles

Question 45

Osmolality

Answer 45

total concentration of solutes

Question 46

Hypotonic

Answer 46

a solution with less fixed particles body tissues

-a cell in a hypotonic solution will swell and possibly lyse (RBC can swell to about twice their original size)

Question 47

Hypertonic

Answer 47

A solution with more fixed particles than body tissues

- a cell in a hypertonic solution will shrink (crenate)

Question 48

Facilitated diffusion

Answer 48

Particles too large to go through pore directly need to be transported.

• The speed of transport depends on the size of the gradient AND the number of transporters.
• Passive process - does not require ATP

Question 49

Transport maximum

Answer 49

Once all transporters are occupied, transport reaches maximum speed (Vmax), like saturation of an enzyme system. Hormones can influence transporters via increase or decrease of transporters

Question 50

Active transport

Answer 50

Requires ATP

Question 51

Primary active transport

Answer 51

Requires ATP directly

• Proteins called ATPases split ATP and uses the energy in the gamma bond to transport ions against their electrochemical gradient.
• Examples include: Na/K ATPase, Ca2+ ATPase and H+ ATPase.

Question 52

Secondary active transport

Answer 52

It requires the chemical energy from ATP does not itself split the ATP. Instead, secondary active depends on the gradient generated by a primary active transporter. - The Na+/K+ pump maintains a large inward Na+ gradient. As Na+ enters cell along its gradient other substances are co-transported against a gradient by the secondary active transporter. If a molecule like glucose moves in with Na then the transporter, in this case the sodium glucose transporter (SGLT), then the terms symporter or cotransporter can be used. Glucose, galactose, amino acids, neurotransmitters, nucleic acids and Cl can be moved across a membrane by a symporter with Na+. An antiporter or counter-transporter, moves a substance out of the cell, against its gradient as Na+ moves in. Both the Na+/Ca2+ exchanger and the Na+/H+ exchanger are examples of antiporters.

Question 53

structure of an epithelial cell layer.

Answer 53

Epithelial cells exist in layers lining the digestive tract, endocrine glands, and the nephrons of the kidney.

• Epithelial layers have a distinct polarity. The luminal side of the cell faces the space inside a tube, called a lumen. The back and sides of the cell or the basolateral side, sit atop a basement membrane and are closest to the blood supply for the tissue.
• Epithelial cells are anchored together into a sheet by cell junctions called tight junctions. The tightness of the tight junctions determines if molecules can travel between the cells via paracellular transport. For example, the tight junctions in the small intestine get “tighter” as material moves from the duodenum to the ileum.

Question 54

What kinds of transport processes are taking place within this cellular layer?

Answer 54

On the luminal (apical) face of the cell layer is where Na+ coupled secondary active transport are found. These proteins are essential for the absorption or reabsorption of substances into the cell.

The basolateral face contains primary active transporter, most typically the Na/K ATPase.

There may also be transporters the allow the substance that was transported across the luminal side to also cross the basolateral side. For example, in the proximal tubule, the Na/K- ATPases used chemical energy to establish a sodium gradient. The SGLT uses the Na gradient to transport glucose into the tubule cells, thereby generating a glucose gradient. Then glucose leaves via the basolateral GLUT transporter which is a facilitated diffusion protein for glucose.