Unit 1 Objectives Flashcards
What is the role of the cell/plasma membrane?
- semipermeable structure that separates intracellular and extracellular components (lipid bilayer with integral and peripheral proteins) and is a barrier to water-soluble molecules
- proteins serve as receptors (hormones, growth factors, neurotransmitters), channels/carriers, enzymes, anchors (scaffolding to maintain shape), and antigens (signs/recognition)
- **cholesterol provides fluidity for proteins
What is the role of the nucleus?
- the control center for the cell
- contains genetic material (DNA dispersed in nuclear matrix called chromatin)
- site for RNA synthesis
What is the structure and function of the mitochondria?
- powerhouse of the cell; contains enzymes needed for capturing energy from food and converting it to cellular energy
- contains inner and outer membrane (inner membrane contains folds called cristae which allow for greater surface area)
- where vast majority of ATP production occurs
- where O2 is used and CO2 is produced
- contain their own DNA (that is distinct from chromosomal DNA found in nucleus) and ribosomes and are self-replicating
What is the role of ribosomes?
- small particles of nucleoproteins (rRNA and proteins) that are held together by a strand of mRNA
- free ribosomes: involved in protein synthesis which remains in the cell as cytoplasmic structural or functional elements
- ribosomes attached to ER: translate mRNAs that code for proteins to be bound in membranes or destined for secretion
What is the role of the endoplasmic reticulum (ER)?
- a tubular connection system for transporting various substances from one part of the cell to another
- large surface area and multiple enzyme systems attached to ER membranes also provides machinery for many cellular metabolic functions
- 2 types: rough and smooth ER
What is the role of the Golgi apparatus?
- function in association with the ER
- modifies substances delivered from the ER via transport vesicles and packages them into secretory granules or vesicles
- produces large carbohydrate molecules that are added to proteins produced by the rough ER to form glycoproteins
What is the role of lysosomes?
- “digestive organelles in the cell”
- contain hydrolytic enzymes that break down excess and worn-out cell parts as well as foreign substances that are taken into the cell
What’s the role of proteosomes?
- cytoplasmic protein complexes that are not bound by membranes
- responsible for proteolysis of malformed and misfolded proteins and have roles in many cellular responses and events
What are the components of the cytoskeleton?
microtubules, microfilaments, and intermediate filaments
What’s the role of microtubules?
- slender and rigid tubular structures composed of globular proteins called tubulin
- development and maintenance of cell form
- participation in intracellular transport mechanisms
- formation of the basic structure for several complex cytoplasmic organelles, including cilia, flagella, and centrioles
What are the roles of microfilaments?
- composed of actin, which contributes to cell motility, positioning of organelles in the cell, and cell shape and polarity
- actin microfilaments in association with thick myosin filaments contribute to muscle contraction
What’s the role of intermediate filaments?
- a heterogenous group of filaments with diameter sizes between those of microtubules and actin filaments
- have structural and maintenance functions that are important in tissue, cellular, developmental, and differentiation processes
- very responsive to cellular stress, such as heat, radiation, toxins, pathogens, and oxidation
A) Trace the pathway for cell communication beginning at the receptor and ending with the cellular response (G-PROTEIN-LINKED RECEPTORS)
B) Explain why the process is often referred to as signal transduction
A) G-protein linked receptor pathway (MOST COMMON):
1. Ligand (hormone/growth factor/neurotransmitter acting as the “first messenger”) that is attached to the receptor binds to guanine nucleotide/G-protein 2. Diphosphate nucleotide becomes triphosphate nucleotide when ligand binds to G-protein 3. This in turn results in activation of an intracellular enzyme, adenylate cyclase 4. The activation of adenylate cyclase catalyzes a reaction, converting ATP to cAMP (“second messenger”) 5. cAMP activates kinase (adds phosphate group/phosphorylates proteins) 6. Alterations in enzyme activity occur, ion channels open 7. TARGET CELL RESPONSE
B) An extracellular signal has to get across the membrane/is transduced to the inside of the cell in order to elicit a cellular response
Trace the pathway for cell communication beginning at the receptor and ending with the cellular response (ENZYME LINKED)
- Enzyme-linked receptors are transmembrane proteins with their ligand binding site on the outer surface of the cell membrane
- this receptor has intrinsic activity/linked to an enzyme
- converts an extracellular signal to an internal response
- tyrosine kinase: most frequent enzyme, which phosphorylates intracellular proteins and changes the action of the cells
- utilized by many growth factors
- important in some tumorigenesis mechanisms
A) Trace the pathway for cell communication beginning at the receptor and ending with the cellular response (ION LINKED)
- Receptor acts as a gated channel for ion flow across the membrane (involved in the rapid synaptic signaling between electrically excitable cells- many neurotransmitters mediate this type of signaling)
- ligand binding transiently opens channel allowing ion flow
- convert extracellular signal to internal response
- involved in neuron conduction & muscle contraction
Describe the function of G-proteins and second messengers in signal transduction
- G-proteins act as molecular switches inside cells and are involved in transmitting signals from a variety of stimuli outside a cell to its interior
- Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules (the first messengers). Second messengers are responsible for the actual cell response.
Describe mechanism of membrane transport associated with diffusion
- a type of passive transport
- movement of molecules cross membrane from high concentration to low concentration (always requires a gradient)
- used for lipid soluble molecules (steroids, thyroid hormones, gases, and alcohol)
- uncharged small water- soluble molecules via nonspecific protein channels can diffuse through the membrane
- larger gradients & heat accelerate diffusion
Describe mechanism of membrane transport associated with osmosis
- Diffusion of water toward higher solute concentration
- solutes create an osmotic force that attracts water
- osmolarity of extracellular fluids has great impact on cells
** REMEMBER: water always follows sodium (Na+), glucose, urea (large and polar), and proteins!!! These are the main determinants of osmosis.
Describe mechanism of membrane transport associated with endocytosis
Type of vesicular transport; cell membrane extends around material and internalizes/ engulfs extracellular materials
Ex. White blood cells with phagocytosis (pg. 17)
Forms a vesicle, then the vesicles may fuse with a lysosome for chemical breakdown
Describe mechanism of membrane transport associated with exocytosis
The mechanism for secretion of intracellular substances into the extracellular spaces
Important in removing cellular debris and releasing substances, such as hormones, synthesized in the cell (secretion—endocrine/exocrine glands)
Describe mechanism of membrane transport associated with faciltated diffusion
- carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids)
- similar to simple diffusion with using a concentration gradient without energy but it requires a carrier protein
- molecule binds to receptor site on carrier protein
- protein changes shape, molecule passes through
- receptor sites are highly specific to certain molecules and saturable
- Example: for diabetics, if insulin isn’t bound to this transporter, it doesn’t work. It needs insulin to move glucose into the cell.
Describe primary active transport
Energy used to move substrate against gradient
Example: Na+/ K+ ATPase membrane pump (moves sodium from inside the cell to the extracellular region where its concentration is approximately 14 times greater than inside; the pump also returns potassium to the inside where its concentration is approximately 35 times greater than it is outside the cell)
Other examples: Ca 2+ ATPase, H+/K+ ATPase
Describe secondary active transport
Gradient established from primary active transport (Na+) used to move second substrate against gradient/uphill
Indirectly requires energy (ATP)
- this mechanism uses membrane transport proteins, and they have two binding sites: one for sodium and the other for the substance undergoing secondary transport
Examples: symport/cotransport (same direction of sodium) and antiport/countertransport (opposite direction of sodium)
Name and describe the two types of secondary active transport systems with examples
1) cotransport/symport—> sodium and the solute are transported in the same direction (Example: Na+/glucose transport)
2) countertransport/antiport—> sodium and the solute are transported in opposite directions
(Example: Ca 2+/ Na 2+)
Describe the function of ion channels
Definition: protein molecules that span across the cell membrane allowing the passage of ions from one side of the membrane to the other
Process:
cell membrane at its resting potential
- depolarization is initiated by a stimulus, which makes the membrane potential more positive
- causes the opening of Na+ channels results in 3 Na+ entering the cell—> reduction of resting potential = “depolarization” (makes inside positive, outside negative)
-simultaneously, opening of K+ channels results in 2 K+ exiting—> increase in membrane potential= “repolarization” (going back to normal resting potential state)
- Na+ activation gates close
-reestablish the resting membrane potential (negative inside, positive outside)
Describe the resting membrane potential state
- expressed as ICF compared to ECF
- excess negative charge inside the cell
- created and maintained by the Na+/K+ ATPase pump
- negative potential voltage inside: (-70mV)
- membrane is polarized
Relate the function of ATP to cell metabolism
Function: usable energy in phosphate bonds in cellular respiration
Formed in three major pathways:
-Glycolysis: results in 2 total pyruvate, 2 total NADH, and (net) 2 ATP for each pyruvate molecule (4 total ATP)
- Citric Acid: results in 4 NADH, 1 FADH2, and 1 ATP per pyruvate
- ETC: flow of protons across membrane into matrix drives ADP phosphorylation—> 32 ATP; H+ protons combine with O2 to form water as the product
Describe action potential
- Involve rapid changes in the membrane potential
- Local changes in membrane potential result from:
- neuron stimulation/inhibition, temperature, light, pressure, etc.
- due to opening/closing of specific ion channels
- opening of Na+ channels results in 3 Na+ entry—> reduction of resting potential = “depolarization”
- opening of K+ channels results in 2 K+ exit—> increase in membrane potential = “repolarization” back to the resting state
What does an action potential result in?
The sweeping of depolarization to a threshold down a cell membrane results in nerve impulse in neurons and contraction in muscle (action potential)
Compare the processes involved in aerobic and anaerobic metabolism
Glycolysis: anerobic process and occurs in the cytoplasm
Citric Acid Cycle: aerobic conditions; occurs in the mitochondrial matrix
ETC: aerobic, occurs on the inner mitochondrial membrane
