Organelles and Compartmentalization

Define organelles and some examples of it

Discrete, serpate subunits in cells that each have different chemical reactions, pH, enzymes and functions aka specalized for particular function

Organelles include the nuceli, chloroplast, mitochondria, vesicles, ribosomes, and the plasma membrane.

What is not considered organelles?

Cell wall, cytoplasm, cytoskeleton

Explain the function and structure of phagocytic vacuoles

Phagotic vacuoples are temporary organelles formed by phagocytosis in which foreign particles are ingested and fused with a phagolysosome which destroys the ingested particle. The phagocytic vacuole and phagolysosome is a space within cell where antimicrobial activity can take place at low pH without disrupting other metabolic processes.

What does the centrifugation do?

Seperates organelled based on relative density (not the size). It spins at very high speeds. By seperating organelles in cell fractionation, scientsists can isolate organelles and other sub-cellular compenents to observe their function and analyze their biochemical activities

List the advantages of seperating the nucleus and cytoplasm into various comparmentents

Nucleus

• Safeguard the DNA

• mRNA must be modified in post transcriptional modifications for translation (DNA must be in nucleus so when it leaves nuclear pore, mRNA is already modified for protein synthesis)

• In prokaryotes this is not necessary because mRNA does not undergo post transcriptional modifications

Cytoplasm

• Enzyme and substrates need specific environmental factors (pH level and temperate) such as lysosomes to function.

• Organelles with their contents can move

• Increases surface area if compartmentalization so more enzymes can act (more metabolic processes)

• Phagocytic vacuole and phagolysosome provides contained space for antimicrobial activity to take place at low pH without disrupting other metabolic processes

Outline the functional benefits of the nucleus double membrane

• Contains many pores that are very small and numerous (1/3 of nuclear membrane’s surface area) that makes it possible for rapid movement of moleciles between nucleus + cytoplasm (mRNA for example) and vice versa (proteins/ATP/some hormones)

• Made of one membrane that is folded to form double structure.

• Membrane is continous across inner and outer surfaces so it can connect with the ER

• Inner membrane has DNA + nucleolus and lined by nuclear lamina (fibrous protein filaments for strucural support). Only in animal cells.

• Nuclear envelope dissascoiates into small vesicles for mitosis/meisosis for chromosomes to interact with spindle fibres in cytoplasm.

Explain the structure and function of free ribosomes

• Sites of protein synthesis

• Many ribosomes are free in cytoplasm (not bounded to rER) and are part of polysomes (groups of ribsoomes that are translating same mRNA for cell that needs multiple copies of particular polypeptide.

Explain the importance of compartmentalization in eukaryotic cells.

Comparmentalization enables different metabolic processes to occur simultaneously in sperate organelles. It enhances cellular efficiency by concentrating enzymes in specific organelles and keeping substrates and reactants in close proximity. It also provides protection for cellular processes by isolating harmful substances from vital compoenents and seperating potentially damagaing reactions from the cytoplasm.

Describe the role of the organelles in the rough endoplasmic reticulum in protein production.

The surface of rER has ribosomes which are sites of protein synthesis by reading mRNA codons and translating them into polypeptide chains. As proteins are synthesizes, they are threaded into rER’s lumen (internal space) to isolate the proteins for processing. Inside, they are folded into correct 3-D shape and modified. The rER transports the synthesizes proteins to golgi apparatus for further processing/sorting.

Describe the role of a lysosome in cellular digestion.

Lysosome contains digestive enzymes in an acidic envrionment that catalyzes hydrolysis (hydroytic enzymes). It breaks down/digests waste materials, excess/worn out organelles, food particles, and engulfed virus/bacteria. It is involved in cell processes like secretion, membrane repair, cell signalling, and energy metabolism.

Discuss the role of the smooth endoplasmic reticulum in lipid synthesis and detoxification.

sER has structure made of interconnected tubules without ribosomes. This large tubular netowrk provides large surface area for reactions.

Lipid synthesis: Synthesizes phospholipids, cholesterol, and steroid hormones. It containtains the enzymes necessary for lipid synthesis

Detoxification:Contains enzymes that breaks down toxin substances by convertin lipid-soluble toxins to water-soluble compounds. It enables the excretion of harmful substances from cells.

Explain the adapations of the mitochondria that allows it to faciliate cellular respiration

Outer mitochondrial membrane: Contains transport proteins that move pyruvate into mitochondria where decarboxylation takes place and hydrogen is removed (oxidation reaction). This hydrogen is then split into H+ and electrons for ATP synthesis

Inner mitochondrial membrane: Split H+ and electrons are passed along the electron transport chain, a sequence of proteins that releases energy as it pumps protons into the space between the two mitochondrial membranes (intermembrane space). Electron carriers are used in the ETC. ATP synthase is also located here for ATP sythesis when electrochemical gradient is made.

Cristae: Tubular regions that surround membrane that increases surface area for reactions due to its multiple folds

Matrix: Contains enzymes and carriers that are needed for Krebs cycle (aerobic respiration in which smaller amounts of ATP is made)

Explain the adapations of the chloroplast that allows it to faciliate cellular respiration

Double membrane on outside of chloroplast: Isolates working parts and enzymes of chloroplast from surrounding cytoplasm so chemical reactions can take place simultaneously and independently from eachother. It allows the seperation of light-harvesting activity in chloroplasts in the thylakoid (light dependent) from enzymes/substrates of Calvin cycle (light-independent reaction) in stroma.

Tylakoids: Extensive membrane surface area due to its multiple folds allows for greater absorption of light by photosystems. It is organized into flat, compact, circular piles called the grana.

Grana: Loosely arranged in stroma region with seperate grana connected by lamellae. Contains chlorophyll.

Chlorophyll: Photosynthetic pigment that absorbs light energy is in the grana and they are grouped together in structures called photosystems. The light energy absorbed by thylakoid (thanks to large surface area) excites electrons to be pass down the electron transport chain that causes H+ to be pumped into thylakoid for electrochemical gradient needed for ATP synthesis.

Stroma: ATP used for Calvin cycle that ultimately leads to production of glucose. The stroma is the cytoplasm space in chloroplast that has appropiate enxmes and optimum pH level for Calvin cycle to take place.

Explain how compartmentalization in eukaryotic cells enhances cellular efficiency.

Compartmentalization creates specialized environments within organelles that create optimized conditions for specific biochemical reactions.

It concentrates enzymes and substrates in specific areas that can increase reaction rates.

Maintains distinict internal environments for different cellular processess

Explain how the structure of the Golgi apparatus allows it to function

It contains flatteneed membrane sacs called cisternae that varies in shape and organization in different cell type. One type fuses with vesicle membranes of rER to modify proteins. At the opposite side, vesicles are formed from plasma membrane and contain proteins for transport for secretion. Proteins enter the golgi apparatus on side facing the rER and exit the oposite way that faces plasma membrane. They are transferred from one cisterna to the next with each cisterna containing different enzymes that catalyzes different types of protein modification.

The proteins can do: glycosylation (add/remove of sugar from protein), sulfation (adding sulfate groups), or phosphorylation (adding phosphate group).

Some golgi-mediated modification can act as signals to direct proteins to final desitination within cells like lysosomes or plasma membrane.

Explain the structure and function of vesicles and clathrins

Veiscles are made by receptor-mediated endocytosis in which a protein or complex of proteins binds to the receptor on the cell surface such as clathrin. This protein causes the membrane of this cell region to invaginate (tucking in surface/membrane) to form a clathrin-coated pit. The ivaginated membrane eventually breaks off and fuses to form a vesicle from either the Golgi body or plasma membrane.

Some hormones, transport proteins, and antibodies use receptor-mediated endocytosis to get intside the cell and can also be used by viruses/toxins.

List examples of vesicles and their function

Peroxisoms
Lysosomes
Transport vesicles
Secretory vesicles