Mcat Bio: Eukaryotic Cell

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Main difference between pkts and eukyts

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Presence of a nucleus in eukyts

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Features of a nucleus

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- Contains all the DNA of the cell (w/ exception of a small amt of mitochondrial DNA) - Wrapped in a double phospholipid bilayer called the nuc. Envelope/membrane - membrane perforated with large holes called nuclear pores - allow RNA to pass through but not DNA - conatins an area called the nucleolus, which is not separated from the nucleus by a membrane

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Features of a nucleolus

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- site of rRNA transcription and ribosome subunit assembly.

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Three types of endocytosis

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- Phagocytosis - Pinocytosis - Receptor mediated endocytosis

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Features of endocytosis

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- cell membrane protrudes outwards to engulf matter - Only certain specialized cells can perform this (eg. macrophages and neutrophils) - Trigger is proteins On the particulate matter which bind to receptors On the phagocytotic cell - Once engulfed, membrane bound body is called a phagosome

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Features of pinocytosis

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- Intake of water through invaginations - Performed by most cells In a nonselective fashion

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Features of receptor mediated endocytosis

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-Refers to specific uptake of macromolecules such as hormones and nutrients - Ligand binds to receptors and is moved to a clathrin coated pit, which invaginates

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Fxn of clathrin

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- Stabilizes the invagination by forming a polymer net

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Difference between phagocytosis and receptor mediated endocytosis

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- In Receptor mediated endo., purpose is to absorb the ligands - In phago. ligands serve as signals to absorb the particulate matter to which the ligands are attached

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Features of the granular ER

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- Contains attached ribosomes to cytosolic side hence the granular appearance. - site of translation of many proteins, which are propeled into the ER lumen as they are translated. - These proteins are tagged with a signal sequence and possible glycosylated and moved to the golgi via transport vesicles.

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Activities performed on proteins in the Golgi

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- Proteins are organized and concentrated as they move from one cisterna to another. - Proteins are distinguished based on their signal seq. Those w/o signal sequence are packaged and expelled in a process called bulk flow - Golgi may modify proteins by glycosylation, removal of amino acids, and polysaccharide formations.

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What is done with the proteins after they are processed by the Golgi

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- End result of processing by Golgi is a vesicle filled with proteins. The vesicles may be expelled via secretory vesicles, released from the Golgo to mature into lysosomes or transported to other parts of the cell.

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Features of secretory vesicles.

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- Aka zymogen granules - release contents through exocytosis - are incoporated into the cell membrane and thus act as a mechanism to provide the membrane with lipids and proteins.

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How is the cell membrane recycled

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Endocytosis results in portions of the membrane shuttled back to the golgi Exocytosis results in membrane being replenished

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Constitutuve vs regulated secretion

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-Constitutive sec: process by which secretory vesicles are released in a continuous manner - Regulated: process by which vesicles are released in response to a stimulus

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Lysosomes

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- contain acid hyrolases (lipases, proteases,…) - break down macromolecules - have an interior pH of 5 - Material not degraded is expelled - In some cases, will rupture and kill the cell in a process known as autolysis

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Fxn of smooth ER

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- Aids in conversion of glucose from glycogen (contains glucose 6 phosphatase) - Produce triglycerides, which are stored as fat droplets - In conjuction with cytosol, aids in production of cholesterol and its subsequent transformation to other steroids - Transports phospholipds from the cytosol side to the other side - Aids in the detox through oxidation

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Peroxisomes

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- Vesicles in the cytosol which grow by incorporating lipids and proteins in the cytosol - Self-replicate - Involved in production and breakdown of H2O2 - Inactivate toxic substances, regulate O2 conc, metabolize lipids, nitrogenous bases and carbs.

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Cytoskeleton

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- Network of filaments in the cell - anchors the membrane proteins and other cellular components, moves components within the cell, moves the cell itself

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Two major types of filaments in the cytoskeleton

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- Microtubules and microfilaments

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Features of microtubules

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- Larger than microfilaments, made of tubulin Examples include mitotic spindle, flagella and cilia

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Tubulin in microtubules

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- Tubulin is a globular protein which polymerizes into long straight filaments In certain conditions. These filaments lie alongside each other to form a tube. - Has a spiral appearance due to alpha and beta types of Tubulin which alternate

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Structure of flagella and cilia

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- Is made of microtubules - Main structure - anoxeme, contains nine pairs of microtubules arranged concentrically around two indy. Microtubules in a 9+2 arrangement - Cross bridges made of dynein connect each of the outer pairs to their neighbours. - Cross bridges cause a sliding motion causing a whip like motion in cilia and wiggle like motion in flagella

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+ and - end of a microtubule

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- The -ve end attaches to the MTOC (microtubule oranizing center). Microtubule grows away from the MTOC at its +ve end. - MTOC in animal cells is the centrosome. Centrioles fxn in the production of flagella and cilia but are not necessary for microtubule prod.

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Microfilaments

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- Predominantly actin -Produce the contracting force in muscle, active in cytoplasmic streaming, phagocytosis, and microvilli movement

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Define cytoplasmic streaming

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Flowing of cytoplasm in eukaryotic cells. This occurs in both plant and animal cells. It creates cytoplasmic reorganization during cell reproduction. In unicellular eukaryotes like amoeba, it provides the mechanism for cell locomotion. It aids in the delivery of nutrients, metabolites, and genetic information to all parts of larger plant cells

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Difference between eukaryotic flagella and pkytic flagella

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- Eukytic flagella are made of microtubules and undergo a whip-like action - Pkytic are made of flagellin and rotate

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Three types of cellular junctions

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1. Tight jxn 2. Desmosome 3. Gap jxn

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Features and fxn of tight jxn

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- are the closely associated areas of two cells whose membranes join together forming a virtual impermeable barrier to fluid - Fxns: 1. Hold cells together, 2. They prevent the passage of molecules and ions through the space between cells, 3. They block the movement of integral membrane proteins between the apical and basolateral surfaces of the cell, allowing the specialized functions of each surface - found in epithelia of kidneys, intestines, bladder

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Features and fxn of desmosome

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- Joins two cells at a single point - Attach directly to the cytoskeleton - Usually accompany tight jxn's and are found in cells which experience stress eg. skin and intestinal epithelium

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Features and fxn of gap jxn

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Small tunnels connecting cells which allow passage of water and small substances. - Gap jxn's in the cardiac muscle provide for quick spread of action potential

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Endosymbiont theory

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- Hypothesizes that mitochondria and chloroplasts originated as separate prokaryotic organisms which were taken inside the cell as endosymbionts

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DNA of mitochondria

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- Mito has its own circular DNA, no histones or nucleosomes. - DNA codes for mito RNA which is different from RNA in rest of cell. Thus mito's have their own ribosomes - Most protein used by mito is however coded for by nuclear DNA not mito DNA - Codons in mito DNA are different from codons in nuclear DNA

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Antibiotics which block translation by pkyt ribosomes but not eukyt ribosomes will have what effect on mitos?

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- Will block translation in mito

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Structure of mito

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- Surrounded by two phospholipid bilayers - Inner membrane invaginates to form cristae - Intermembrane space exists between outer and innter membrane