Eukaryotic cell Flashcards Preview

MCAT bio > Eukaryotic cell > Flashcards

Flashcards in Eukaryotic cell Deck (45):


1. Phagocytosis (Macrophages and Neutrophils)- receptors on cell membrane attach to antibodies or complement proteins present on particulate matter. Membrane protrudes outward to engulf. Ligands in phagocytosis exist only to act as signals to initiate phagocytosis of other particles. 2. Pinocytosis- nonselective. Performed by most cells. Invaginations in membrane engulf extracellular fluid. 3. Receptor-mediated- uptake of macromolecules (hormones, nutrients). Ligand binds to receptors on cell. Clathrin protein coats cell side of membrane and helps form a coated vesicle. Purpose is to absorb the ligand.



Wrapped in a DOUBLE phospholipid bilayer. RNA exits through nuclear pores.



Inside of nucleus. rRNA transcribed and ribosomes assembled in nucleolus. Dissappears during prophase (DNA wound up).


Not to be confused with the nucleoid in bacteria.


Smooth ER

Site of lipid synthesis, including steroids. The smooth ER also helps detoxify some drugs and contains G-6-Phosphatase (G6P> glucose) in liver, renal tubule epithelial cells, intestinal epithelial cells.


Rough ER

Separates cytosol from ER lumen/cisternal space. Rough ER has ribosomes attached to its cytosol side and synthesizes virtually all proteins not used in the cytosol. Proteins translated and moved through lumen towards golgi. Rough ER tags proteins with signal sequence and sometimes glycosylate proteins. Vesicles bud off of ER and transport proteins to golgi.



Golgi is a series of flattened, membrane bound sacs. The Golgi modifies and packages proteins (in secretory vesicles) for use in other parts of the cell and outside the cell.( ex. mitochondria or even back to ER). Golgi organizes and concentrates proteins as they are shuttled by transport vesicles progressively outward from one compartment of the Golgi to the next. Can gylcosylate and remove aas from proteins.



Lysosomes (pH 5) are specialized vesicles that bud from Golgi that contain vesicles with enzymes (acid hydrolases) that are capable of breaking down every macromolecule in cell. 1-Fuse with endocytotic vesicles and digest contents. 2-Take up and degrade cytosolic proteins in an endocytotic process. 3-Can rupture under certain conditions to release their contents into the cytosol to kill the cell (autolysis). Important in forming organs and tissues (killing cells between fingers).



Vesicles in cytosol. Grow by incorporating lipids from cytosol. Self-replicate (do not bud off from golgi like lysosomes). Involved in breakdown and production of hydrogen peroxide. Peroxisomes inactivate toxic substances such as alcohol, regulate O2 concentration, play a role in synthesis and breakdown of lipids, and in metabolism of nitrogenous bases and carbohydrates.


Cytosol vs ER

Cell can be divided into 2 sides: the cytosol and ER lumen. In order to reach the cytosol, a substance must cross a membrane via passive or facilitated diffusion, or active transport, but it can reach the ER lumen via endocytosis without ever transporting across a membrane.



The cytoskeleton is a network of filaments that determines the structure and motility of a cell. Two major types of filaments in the cytoskeleton are microfilaments and microtubules.



Microtubules are rigid hollow tubes made from a protein called tubulin (globular protein that can polymerize). Have a + end and - end. The - end attaches to a microtubule organizing center (MOTC) and grows away at its + end. A centrosome is an example of a MOTC. Structures made form microtubules: Flagella (wiggle), cilia (whip) Mitotic spindle Microtubules are larger than microfilaments


Flagella and Cilia

Flagella wiggle away directly from cells. Cilia whip laterally away from cells. They are specialized structures made from microtubules. The major portion of both structures is called the axoneme. The axoneme contains 9 pairs of microtubules in a circle around 2 lone microtubules (9+2 arrangement). A protein called dyenin connects each of the outer pairs of microtubules to their neighbor. The cross bridges cause the microtubule pairs to slide along their neighbors creating movement.



Microfilaments produce: 1-Contracting force in muscle. 2-Active in cytoplasmic streaming (responsible for amoeba like movement), phagocytosis and microvilli movement. The major component of microfilaments is composed of the polymerized protein actin.


Tight Junctions

Tight junctions form a watertight seal from cell to cell that can block water, ions, and other molecules from moving around and past cells. Tissue held together by tight junctions may act as a complete fluid barrier. Epithelial tissue in organs like bladder, intestines, kidney are held together by tight junctions in order to prevent waste materials from seeping around cells and into the body. Since proteins can move laterally about the cell membrane, tight junctions act as a barrier to protein movement between the apical (part of cell facing lumen of a cavity) and basolateral surface of a cell (faces outwards towards interstitium).



A type of cell junction. Desmosomes attach directly to the cytoskeleton of 2 cells, joining them at a single point. Desmosomes are like spot welds holding cells together and do not prevent fluid form circulating around all sides of a cell. Desmosomes are found in tissues that normally experience a lot of stress, like skin, or intestinal epithelium. Desmosomes often accompany tight junctions.


Gap Junctions

Gap junctions are small tunnels connecting cells that allow the exchange of small molecules and ions. **Gap junctions in cardiac muscle provide for the spread of the action potential form cell to cell.


Endosymbiont theory

Theory that mitochondria might have evolved from a symbiotic relationship between prokaryotes and eukaryotes. -Mitochondria has circular DNA that replicates independently of the eukaryotic cell -Antibiotics that block translation by prokaryotic ribosomes block translation by mitochondrial ribosomes (and do not block eukaryotic ribosomes)



Mitochondria are the powerhouses of the eurkaryotic cell.

1-Krebs cycle takes place in the mitochondiral matrixand

2-Electron transport chain occurs in the inner membrane. Protons pumped into innermembrane spance and ATP formed in matrix.

Mitochondira has circular DNA that replicates independently of the eukaryotic cell. Code for mtRNA that is distinct from RNA from rest of cell (have their own ribosomes). Code for different codons than rest of cell providing an exception to the universal genetic code. MtDNA is passed on maternally.

A image thumb

Extracellular Matrix

Molecules that surrounds the cell and is formed by the cell itself.


1. Glycosaminoglycans, proteoglycans- make up over 90% of matrix by mass. Provide pliability to matrix.

2. Structural proteins- Collagen is the most common structural protein in extracellular matrix.

3. Adhesive proteins- help cells within a tissue stick together.



Cell communication

Communication is accomplished chemicaly via 3 types of molecules

  1. Neurotransmitters- neuronal communication tends to be rapid direct and specific
  2. Local mediators- local communication is via the paracrine system. 
  3. Hormones- hormonal communication is slow, spread throughout the body, and affect many cells and tissues in any different ways.


Paracrines System

Local mediators (proteins, other aa derivatives, FAs ex is prostaglandins) are released into interstitial fluid and act on neighboring cells a few millimeters away. 

Growth factors and lymphokines are other examples of local mediators.

Prostaglandins are fatty acid derivatives that act as local mediators. Prostaglandins affect smooth muscle contraction, platelet aggregation, inflammation and other reactions.

Aspirin inhibits prostaglandin synthesis (acts as an anti-inflammatory).



A neuron is a cell capable of transmitting an electrical signal from one cell to another via electrical or chemical means. It cannot divide. It depends almost entirely upon glucose for its chemical energy (comes in via facilitated transport). Does not depend on insulin to obtain glucose.


  1. Dendrites receive signal to be transmitted
  2. Signal is transferred to the axon hillock, if the stimulus is great enough, the axon hillock generates an action potential in all directions, including down the axon. 
  3. The axon carries the action potential to a synapse which pass the signal to another cell. 


Membrane resting potential of a neuron

Q image thumb

At resting potential the inside of the membrane has a negative voltage compared to the ouside of the membrane. 

It is established mainly by an equilibrium between passive diffusion of ions across the membrane and the Na+/K+ pump (3 Na+ out of cell, 2 K+ in, active transport). As the electrochemical gradient of Na+ becomes greater, the force pushing the Na+ back into the cell also increases. The rate at which Na+ passively diffuses back into the cell increases until it equals the rate at which it is being pumped out of the cell. Same with K+. When all rates reach equilibrium, the inside of the membrane has a negative potential compared to the outside. 



Voltage gated sodium channel

The membrane of a neuron contains integral membrane proteins called voltage gated sodium channels. These proteins change configuration when the resting potential across the membrane is disturbed, allowing Na+ to flow through the membrane.


Action potential of neuron

  1. Depolarization- Voltage-gated sodium channels change configuration to allow more Na+ inside the cell for a fraction of a second, Na+ flowing into the cell causes more sodium channels to change configuration allowing more Na+ into the cell in a positive feedback mechanism. Since the concentration of Na+ is moving towards equilibrium and the K+ concentration remains higher inside the cell, the membrane potential reverses polarity so that it is positive on the inside and negative on the ouside. 
  2. Repolarization- The potassium channels are less sensitive to voltage change so they begin to open at the time most of the sodium channels are closing. K+ flows OUT of the cel making the inside more negative.
  3. Hyperpollarization- Because the K+ channels are slow to close the inside membrane becomes even more negative than the resting potential (for a fraction of a second) 
  4. Passive diffusion returns the membrane to its resting potential.

**Throughout the action potential, the Na+/ K+ pump keeps working**


Action potential 

Q image thumb

  1. Membrane is at rest. Na+ and K+ channels are closed.
  2. Na+ channels open and cell depolarizes.
  3. K+ channels open as Na+ sodium channels begin to inactivate.
  4. Na+ channels are inactivated. Open K+ channels repolarize the membrane.
  5. K+ channels close and the membrane equilibriates to its resting potential. 

**Na+/K+ pump working throughout the action potential 

**Action potential begins at axon hillock 


Absolute refractory period

Once an action potential has begun, there is a short period called the absolute refractory period in which no stimulus will create another action potential.


Electrical Synapse

 Electrical synapses are uncommon and they are composed of gap junctions between cells. Cardiac muscle, visceral smooth muscle, and very few neurons in the CNS contain electrical synapses. Since they don't involve diffusion of chemicals, they transmit signals much faster than chemical synapses and in both directions. 


Chemical synapses

A chemical synapse is unidirectional and the slowest step in transfer of a nervous signal. In a chemical synapse, small vesicles filled with neurotransmitter rests just inside the presynaptic membrane. The membrane near the synapse contains an unusually large number of Ca2+ voltage gated channels.

1. When an action potential arrives Ca2+ voltage gated channels are activated allowing Ca2+ to flow into the cell.

2. The influx of ca2+ causes some of the neurotransmitter vesicles to be released through an exocytotic process into the synaptic cleft (space between presynaptic and postsynaptic neurons) and diffuses via Brownian motion (random motion of molecules). 

3. When the neurotransmitter attaches to the neurotransmitter receptor proteins on the postsynaptic membrane, the post synaptic membrane becodmes mroe permeable to ions. (The neurotransmitter attaches for only a fraciton of a second and it is released back into the synaptic cleft) 

4. Ions move across the postsnyaptic membrane, completing the transfer of the neural impulse. 



Neurotransmitter mechanisms

  • A single synapse usually releases only one type of neurotransmitter and is designed iether to inhibit or to excite, but not both. 
  • Although, some neurotransmitters are capable of inhibition or excitation depending on the type of postsynaptic membrane (acetylcholine, a common neurotransmitter, has an inhibitory effect on the heart, but an excitatory effect on the visceral smooth muscle of the intestines)



  • Myelin is the electrically insulating sheath that wraps around axons of neurons. Myelin is white matter and neurons are gray matter.
  • Myelin is made from Oligodendrocytes in the CNS
  • Myelin is made from Schwann cells in the PNS

*Only vertebrates have myelinated axons


Saltatory conduction

When an action potential is generated down a myelinated axonm the action portential jumps from one node of Ranvier (the tiny gaps between myelin) to the next. 


Support cells

  1. Microglia- arise from monocytes. They phagocytize microbes and cellular debris in the CNS.
  2. Epedymal cells- epithelial cells that line the space containg the cerebrospinal fluid. These cells use cilia to circulate the fluid.
  3. Satelitte cells- support ganglia (groups of cell bodies in the PNS). 
  4. Astrocytes- star-shaped neuroglia in the CNS that give physical support to neurons and help maintain mineral and nutrient balance in the interstitial space. 
  5. Oligodendrocytes- wrap around axons in the CNS creating electrically insulating sheaths called myelin.
  6. Schwann cells- the cells that form myelin in the PNS. 


The 3 types of neurons

  1. Sensory (afferent) neurons- receive signals from a receptor cell that interacts with its environment. The sensory neuron then transfers this signal to other neurons. 99% if sensory input is discarded by the brain.
  2. Interneurons- transfer signals from neuron to neuron. 90% of neurons int he human body are interneurons.
  3. Motor (efferent) neurons- carry signals to muscle or gland called the effector. Sensory neurons are located dorsally from the spinal cord, while motor neurons are located ventrally.


Simple Reflex Arc of the Somatic Nervous system

A simple reflex arc can have an interneuron or no interneuron. 

  1. Sensory (afferent) neuron's dendrites receives signal from environment (pin prick on finger)
  2. The signal is sent through to the dorsal side of the spinal cord and synapses with an interneuron. (this step is possible, not all simple reflex arcs require interneurons)
  3. The interneuron synapses with the motor neuron, which send the signal through the ventral side of the spinal cord and causes a reflex.


Central Nervous System

The CNS consists of interneurons and support tissue within the brain and spinal cord. The function of the CNS is to integrate nervous signals between sensory and motor neurons. The CNS is connected to the peripheral parts of the body by the PNS.

  • The spinal cord mainly acts as a conduit for nerves to reacht he brain. It  can process limited integrating functions  such as walking reflexes, leg stiffening, and limb withdrawl from pain
  • The lower brain consists of medulla (involuntary breathing), hypothalamus, thalamus, cerebellum (fine motor movements). It integrates subconscious activities such as the respiratory system, arterial pressure, salivation, emotions and reaction to pain and pleasure.
  • The higher brain or cortical brain consists of the cerebrum or cerebral cortex. The cerebral cortex is incapable of functioning without the lower brain. It acts to store memories and process thoughts.

A image thumb

Peripheral Nervous System

The PNS handles the sensory and motor functions of the nervous system. (Parts of the PNS, such as cranial nerves and the spinal nerves, project into the brain and spinal cord.)

PNS can be divided into:

1. Somatic nervous system (voluntary)- designed primarily to respond to the external environment. It contains sensory and motor functions. Its motor neurons innervate only skeletal muscle. The cell bodies of somatic motor neurons are located in the ventral horns of the spinal cord. These neurons synapse directly to their effectors and use acetylcholine for their neurotransmitter. The sensory neuron cell bodies are loctated in the dorsal root ganglion.

2. Autonomic nervous system (involuntary, controlled mainly by hypothalamus)- The sensory portion of hte ANS receives signals primarily fromt he viscdera. The motor portion of the ANS then conducts these signals to smooth muscle, cardiac muscle, and glands.  The ANS is further divided into the sympathetic and parasympathetic systems, most interal organs are innervated by both with the 2 systems working antagonistically.


Sympathetic System of ANS

The sympathetic system deals with "flight or flight" responses. Sympathetic signals originate in neurons whose cell bodies are found in the spinal cord.

It's action on the heart would be to increase beat rate and stroke volume; it works to constrict blood vessesl around the digestive and excretory systems in order to increase bloodflow around skeletal muscles. 


Parasympathetic System

The goal of the PNS is "rest and digest." Parasympathetic activity slows the heart rate and increases digestive and excretory activity.

Parasympathetic signals originate in neurons whose cell bodies can be found both in brain and spinal cord.

*A group of cell bodies in the CNS is called a nucleus, a group of cell bodies in the PNS is called a ganglion.


Pre-ganglionic neurons

Pre-ganglionic neurons are the neurons that extend out from the spinal cord to synapse with Post-ganglionic neurons whose cell bodies are located outside of the CNS. A group of pre-ganglionic neuron cell bodies is called a nucleus.

1. Sympathetic signals originate in pre-ganglionic neurons whose cell bodies are found in the spinal cord

2. Parasympathetic signals originate in pre-ganglionic neurons whose cell bodies rae found in the spinal cord or the brain


Post-ganglionic neurons

Post-ganglionic neurons are located outside of the CNS. A collection of post-ganglionic cell bodies is called a ganglion. 

1. Sympathetic post-ganglionic neuron cell bodies are located lie far from their effectors in the paravertebral ganglion (runs parallel to spinal cord). Or in the prevertebral ganglia in the abdomen.

2. Parasympathetic post-ganglionic neuron cell bodies lie in ganglia near their effectors.


ANS neurotransmitters

  • Acetylcholine is used by all preganglionic neurons in the ANS and by parasymathetic postganglionic neurons. Acetylcholine receptors are called cholinergic receptors. 2 types:
    1. nicotinic- generally found on the postsynaptic cells of hte synapse between the ANS preganglionic and postganglionic neurons and on the skeletal muscle membranes at neuromuscular junction.
    2. muscarinic- found on the effectors of the parasypathetic nervous system.
  • Epineprhrine or norepinephrine (aka adrenaline and noradrenaline) is used by sympathetic postganglionic neurons. Epinephrine receptors are called andrenergic.


The Eye

Path of light in eye: Cornea bends light, light goes through anterior cavity to enter the lens which is flattened by ciliary muscle. 

  • Iris and pupil- iris is made from circular and radial cirular and radial muscles and creates the opening called the pupil.

    • Dark environment- sympathetic nervous system contracts the iris dilating the pupil. 

    • Bright environment- parasympathetic nervous system cotnracts circular muscles of the iris constricting the pupil and screening out light.

  • Ciliary muscle- connected by suspensory ligaments to lens. Relaxed ciliary muscle flattens the lens and increases the focal distance. Contracted ciliary muscle allows lens to become more like a sphere and brings focus point closer to the lens. 
  • Retina- covers the inside of the distal portion of the eye. It contains rods and cones (cones distinguish colors, rods don't) Vitamin A is a precursor to all the pigments in rods and cones. 


Visible Spectrum

390 nm to 700 nm


The Ear

  1. Outer ear- external auditory canal carries sound wave to the tympanic membrane or eardrum.
  2. Middle ear- the tympanic membrane begins the middle ear. The middle ear contains 3 small bones: malleus, incus, stapes, that act to increase the force of the wave (because it is going from air in the outer ear to a more resistant fluid within the inner ear)
  3. Inner ear- sound waves moves through cochlea and the alternating increase and decrease in pressure casuses movement in the membrane. This is detected by the hair cells of the organ of Corti and transduced into neural signals which are sent to the brain. 
    • Semicircular canals- Responsible for balance.