Cell Structure Chapter 6

YOU MUST KNOW Three differences between prokaryotic and eukaryotic cells The structure and function of organelles common to plant and animal cells The structure and function of organelles found only in plant cells or animal cells How different cell types show difference in subcellular components How internal membranes or organelles contribute to cell function How cell size and shape affect the overall rate of nutrient intake and waste elimination http://learn.genetics.utah.edu/content/cells/scale

Prokaryotes Found in the domains Bacteria and Archaea Contain a single, circular chromosome in nucleoid region Contain no membrane-bound organelles Very small in comparison to eukaryotes

Interesting Facts Prokaryotes dominate the biosphere Collective mass outweighs all eukaryotes combined by at least 10 fold More prokaryotes inhabit a handful of fertile soil or in the mouth or skin of a human than the total number of people who have ever lived! Found wherever there is life Especially in extreme environments There are a hundred billion prokaryotes per milliliter of fluid in the human colon.

Eukaryotes Belong to domain Eukarya, includes animals, plants, fungi, protists Membrane bound nucleus containing linear chromosomes Membrane-bound organelles Much larger than prokaryotes Prokaryotes Eukaryotes Plasma Membrane Yes Ribosomes Membrane-bound organelles No Nucleus Size 1-10um 10-100um

The Nucleus Contains DNA Surrounded by a lipid bilayer (membrane) called the nuclear envelope which is connected to the rough endoplasmic reticulum and contains nuclear pores to allow things to enter and leave the nucleus Nucleolus – region (not really a structure) where rRNA combines with proteins to form ribosomal subunits

Ribosomes Composed of rRNA and protein – one large subunit and one small Sites of protein synthesis Can be free-floating or bound to endoplasmic reticulum Free-floating – produce proteins to be used in the cell Bound – produce proteins that will be exported out of the cell

Endoplasmic Reticulum Network or folded membranes and sacs – space between called cisternal space Smooth– no ribosomes associated Metabolism of lipids and carbs Detoxification of drugs and poisons Rough – covered in ribosomes Ribosomes synthesize proteins which are then wrapped in vesicles made of the membrane of the ER

Golgi Apparatus Stacks of flattened sacs of membrane called cisternae Modifies, stores, and ships out proteins Sacs are polar with cis side receiving incoming proteins from the RER and shipping them out from the trans side Camilo Golgi

Release to monomers produced by their reactions back in to the cell Lysosomes Membrane-bound sacs of hydrolytic enzymes to digest unwanted or old molecules and organelles in the cell Release to monomers produced by their reactions back in to the cell Enzymes involved require a low pH to function, so if lysosome breaks open, they do not work Peroxisomes Membrane-bound sacs Transfer hydrogen from compounds to oxygen, forming H2O2 (toxic to cell) Contains enzymes to break down the H2O2 Breaks down fatty acids so that they can be used by the mitochondria Detoxify substances (alcohol) by transferring its hydrogen to oxygen Importance of compartmentalization

Vacuoles Membrane-bound sacs used for various reasons Contractile vacuoles in protists – contracts to expel water out of the cell to prevent lysis in hypotonic environments https://www.youtube.com/watch?v=pahUt0RCKYc Central vacuole in plants – can make up as much as 80% of a cell, used for storage

Mitochondria Sites of cellular respiration – energy conversion from food to ATP 2 membranes – outer and inner Cristae – folds of the inner membrane, increase surface area Matrix – fluid filled inner compartment Contains its own circular DNA and its own ribosomes

Chloroplasts Site of photosynthesis in plants – energy conversion from light to food Also contains its own circular DNA and ribosomes Double membrane structure

Endosymbiotic theory Mitochondria and chloroplasts have many characteristics of prokaryotic cells – circular DNA, ribosomes Double membrane indicates they were engulfed by another cell by endocytosis Eukaryotes arose from one prokaryote engulfing others and the engulfed cells developing specialized functions

Cytoskeleton Network of protein fibers for support, motility, and regulation Microtubules – tubulin fibers, shape and support, tracks for molecules to travel along, separate chromosomes during mitosis and meiosis, form cilia and flagella Flagella – long tails to propel cells Cilia – shorter and more numerous than flagella, can be used to move the cell itself or to move things along outside the cell Both in 9+2 pattern – 9 pairs of microtubules around a core of 2 microtubules

Microfilaments – composed of actin, smaller than microtubules, involved in muscle contractions Intermediate filaments – maintain shape, fix position of oragnelles

Centrosomes – near nucleus, region where microtubules are formed Centrioles – located within centrosomes, used during mitosis and meiosis

Extracellular components Cell wall In plants, composed of cellulose, for shape and support Also in prokaryotes & fungi, composed of peptidoglycan & chitin Plasmodesmata – channels in cell walls between cells to allow passage of materials from one cell to another

Extracellular Matrix (ECM) Animal cells Composed of glycoproteins secreted by cell, mostly collagen Strengthens tissues, allows for transmittal of stimuli into the cell

Intercellular junctions (in animal cells) Tight junctions – two neighboring cells are fused by their cell membranes Desmosomes – proteins that link adjacent cells like rivets, making strong sheets Gap junctions – protein channels connecting adjacent cells so small molecules can pass from one to the next