Mcat Biology-4-Eukaryotic Cell And Nervous System

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Eukaryote

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A member of the domain Eukarya; an organism whose cells contain a nucleus, numerous membrane-bound organelles, and an extensive cytoskeleton. May be unicellular or multicellular.

-Only eukaryotes have nuclei.
-DNA cannot leave nucleus, so transcription must occur in nucleus.
-RNA leaves nucleus through nuclear pores.

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Endocytosis

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General term for any pinching off of the plasma membrane that results in the uptake of material from outside the cell. Includes phagocytosis, pinocytosis, and receptor-mediated endocytosis.

-Phagocytosis: cell membranes protrudes outward to envelope and engulf (antibodies)

-Pinocytosis: extracellular fluid engulfed by small invaginations of cell (nonselective) - taking in small particles

-Receptor mediated endocytosis: specific uptake of macromolecules such as hormones and nutrients

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Exocytosis

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Secretion of intracellular molecules (e.g., hormones, collagen), contained within membrane-bounded vesicles, to the outside of the cell by fusion of vesicles to the plasma membrane.

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Golgi apparatus

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A eukaryotic organelle, consisting of stacks of flattened membranous sacs (cisternae), that functions in processing and sorting proteins and lipids destined to be secreted or directed to other organelles. Also called Golgi complex.

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Secretory vesicles

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may contain enzymes, growth factors, or extracellular matrix components

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Lysosomes

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A small organelle in an animal cell containing acids and enzymes that catalyze hydrolysis reactions and can digest large molecules.

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Endoplasmic reticulum (ER)

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A network of interconnected membranous sacs and tubules found inside eukaryotic cells.

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Rough ER

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The portion of the endoplasmic reticulum that is dotted with ribosomes. Involved in synthesis of plasma membrane proteins, secreted proteins, and proteins localized to the ER, Golgi apparatus, and lysosomes.

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Smooth ER

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The portion of the endoplasmic reticulum that does not have ribosomes attached to it. Involved in synthesis and secretion of lipids.

-Smooth
ER contains glucose 6-phosphatase, the enzyme used in the liver, the intestinal epithelial cells, and renal tubule epithelial cells, to hydrolyze glucose 6-phosphate to glucose, an important step in the production of glucose from glycogen.
-Triglycerides are produced in the smooth ER and stored in fat droplets.
-cholesterol formation
-Phospholipids are all synthesized on the cytosol side of the membrane and then some are flipped to the other side by proteins called phospholipid translocators located exclusively in the smooth ER
-smooth ER oxidizes foreign substances, detoxifying drugs, pesticides, toxins, and pollutants

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The secretory pathway (a model at least)

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1. Protein enters ER while being synthesized by ribosome.

2. Protein exits ER, travels to cis face of Golgi apparatus.

3. Protein enters Golgi apparatus and is processed as the cisternum moves toward the trans face.

4. Protein exits Golgi apparatus at trans face and moves to plasma membrane.

5. Protein is secreted from cell.

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Peroxisomes

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vesicles in cytosol.
-self-replicate.
-production and breakdown of H2O2.
-inactivates toxic substances.
-regulate O2 concentration.
-synthesis/breakdown of lipids.
-metabolism of nitrogenous bases and carbohydrates

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know for MCAT:

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

-rough ER has ribosomes attached to cytosol side and synthesizes virtually all proteins not used in cytosol. proteins syn. on rough ER are pushed into ER lumen and sent to Golgi.

-Golgi modifies and packages proteins for use in other parts of cell and outside the cell.

-Lysosomes contain hydrolytic enzymes that digest substances taken in by endocytosis. Lysosomes come from the Golgi.

-Smooth ER is the site of lipid synthesis including steroids. helps detoxify some drugs. LIVER

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microtubules vs. microfilaments

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Microtubules: larger and involves in flagella and cilia construction and spindle apparatus. Composed of tubulin. (in humans cilia is only found in fallopian tube and respiratory tract)

Microfilaments: squeeze the membrane together in phagocytosis and cytokinesis. Made from actin. Also contractile force in microvilli and muscle. Also active in Cytoplasmic streaming (amoeba-like movement)

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Axoneme

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major portion of each flagellum and cilium, containing 9 pairs of microtubules forming a circle around 2 lone microtubules in 9+2 arrangement

connected by protein called dynein

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eukaryotic vs. prokaryotic flagella

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euk. flagella is 9+2 and prok. flagellum is thin trand of flagellin

euk. flagella undergo whip-like action and prok. flagella rotate

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actin

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polymerized protein that forms a major component of microfilaments

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3 types of junctions/attachments that connect animal cells

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1. tight junctions: watertight seal that blocks water, ions, and other molecules --> complete fluid barrier (ex: epithelial tissue in bladder, intestines, and kidney to prevent waste from seeping into body)
2. desmosomes: spot-welds holding cells together, join 2 cells together at a single point (ex: tissues that experience a lot of stress like skin or intestinal epithelium) STRONGEST
3. gap junctions: tunnels between cells allowing for the exchange of small molecules (ex: cardiac muscle)

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Mitochondria

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-endosymbiont theory
-mitochondrial DNA passed maternally
-2 phospholipid bilayers
-Inner membrane invaginates to form cristae
-Inner membrane holds electron transport chain
-Intermembrane space is between inner and outer membrane

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nucleolus

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subunits of ribosome are assembled

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Intercellular communication

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-Neurotransmitters - nervous system (rapid, specific, short distance)

-local mediators - paracrine system

-Hormones - endocrine system (slow, affect many cells differently, long distance, spread through body)

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Neuron

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-transmit electrical signal

-high specialized and lost capacity to divide

-depends on glucose for chemical energy, but do not depend on insulin to obtain glucose

-dendrites (receive signal), single cell body, 1 axon with many small branches (action potential goes down axon to synapse)

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Action potential

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A rapid, temporary change in electrical potential across a membrane, from negative to positive and back to negative. Occurs in cells, such as neurons and muscle cells, that have an excitable membrane.

-3Na+ out, 2 K+ in

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Electrical synapses

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-Uncommon

-Gap junctions between cells (ex: cardiac, visceral smooth muscle and few neurons in central nervous system)

-Faster than chemical synapses

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Chemical synapses

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-Common

-Unidirectional

-Slowest step in transfer of nervous signal

-Brownian motion (random motion of molecules)