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Transcript
10/5/2015 The Cell • Biology 102 Fundamental unit of life • Smallest unit that displays all the basic elements of life Lecture 5: Cells Cell Theory 1. All living things are made of one or more cells Cell Theory 3. Each new cell arises from the division of another, prepre-existing cell Cell Theory 2. The simplest organisms are made of only one cell; the cell is the functional unit of multicellular organisms Cell Theory 3. Each new cell arises from the division of another, prepre-existing cell Bacteria Drosophila 1 10/5/2015 Cell Types • Two broad categories Prokaryotes • Unicellular • Prokaryotes • All cells identical – no specialized function • Eukaryotes • Lack nucleus, other membranemembrane-bound organelles • Example: bacteria Eukaryotes • May be unicellular • Eukaryotes • Examples: yeast, amoebas May be multicellular • Examples: plants, animals Eukaryotic Cells Eukaryotic Cells • Differ greatly in appearance and function • Differ greatly in appearance and function • 4 basic components in common • 4 basic components in common 1. Plasma membrane 2. Cytoplasm • Isolation • Protection cell but outside the • Sensitivity nucleus • Support • Gatekeeper • • Material inside the Contains the cytosol and organelles 2 10/5/2015 Eukaryotic Cells Eukaryotic Cells • Differ greatly in appearance and function • Differ greatly in appearance and function • 4 basic components in common • 4 basic components in common 3. The nucleus • • 4. Organelles Control center – the • “Organs” of the cell “brain of the cell” • Perform specific Contains the DNA functions • Some bound by membranes Cytoplasm • Everything inside the membrane, except the nucleus • Includes… • Cell Size • Cells are small, but molecules for their chemical reactions are much smaller A LOT more on the membrane later Utah Genetics • Cytosol = liquid portion • Organelles Cell Size Glucose is 108 times smaller than a bacterium • Reactants needed for metabolism are present in low concentrations • Low concentration means reactants don’t collide often • This makes chemical reactions slow • Concentration gets lower as cells get bigger • What happens to chemical reaction rate in cells as cells get bigger? Relative Rate of Reaction • Cell Size Cell Size 3 10/5/2015 Cell Size • Why prokaryotic cells stay small • Eukaryotic cells have found a way around this: membrane--bound organelles membrane • Serve to concentrate reactants in appropriate compartments • Improves cell efficiency Cell Size • This means eukaryotic cells can be larger than prokaryotic cells Cell Size • Still, being small has some advantages • Solutes taken into cells through membrane • Consider 2 cubes (even though most cells are spherical)… 1 µm Cell Size • Complete the following calculations: Cell 1 Cell 2 Surface Area: length x width x 6 Volume: length x width x height Surface Area/Volume 2 µm 1 µm Cell Size • Which cell has the greater surface area? • Which cell has the greater volume? • Which cell has the greater ratio of surface area to volume? 2 µm Cell Size • Volume increases faster than surface area • (x3 vs x2) • So as cells get bigger, the proportion of surface area decreases • Keeps cells small • Cells need surface area to absorb solutes • Less surface area = fewer reactions 4 10/5/2015 Organelles Non--membranous Non Membranous • Cell wall • Cytoskeleton • Cellular extensions • • Cell Membrane • Endomembrane system • Vacuoles Microvilli Double Membrane • Cilia • Nucleus • Flagella • Mitochondria Ribosomes • Plastids • • All cells are surrounded by a cell membrane • Consists of a bilayer made of mostly phospholipids • Critical to cell function • Discussed in great detail later • Also called a plasma membrane Chloroplasts Cell Wall • Cell Wall Plants, fungi, and bacteria are also have cell walls • Animal cells do not Made of polysaccharides secreted through plasma membrane • All have a cell membrane • Non--living Non • Exterior to cell Cell Membrane • • Cell walls of adjacent plant cells stuck together with pectin Cell Wall • Porous • Oxygen, carbon dioxide, water carrying small molecules flow through freely Cell Wall • Adds strength and integrity to cells • Plants, fungi don’t have bones • Allows them to withstand gravity and wind and grow upright 5 10/5/2015 Cytoskeleton • Internal protein network of cells • Stabilize cell’s 33-dimensional shape • Guide vesicles Microtubules • Formed from tubulin subunits 1. Component of cytoskeleton – cell shape, anchor organelles Microtubules Microtubules 2. Intracellular transport with motor proteins 3. Move chromosomes during cell division Microtubules 4. Basis of cellular extensions Intermediate Filaments • >60 different kinds • Resist stretching • Functions: 1. Strength 2. Stabilize organelle position 3. Transport 6 10/5/2015 Microfilaments • Made of actin subunits • Associated with cell movement, changes in cell shape Comparison of Cytoskeletal Proteins Cellular Extensions • Cilia Cellular Extensions • Flagella • Whip--like Whip • Substantially longer than cilia • Move substances in one direction across stationary cells • Only example in human body: sperm • Example: trachea Cellular Extensions • Microvilli • Very small, highly numerous • Increase absorptive surface area • Example: small intestine Ribosomes • Site of protein synthesis • Abundant in cells that produce a lot of protein • Example: human liver cells have on average 13 million ribosomes in each cell! 7 10/5/2015 Ribosomes • Made from rRNA (2 units) and proteins • Polypeptide chain constructed using information provided by mRNA Ribosomes Many ribosomes can read the same strand of mRNA at once • mRNA • Contains information for… • Amino acid sequence • Final destination of protein mRNA Final destination of protein • • mRNA • Final destination of protein somewhere else = mRNA/ribosome complex associates with Bound for cytosol cytosol,, = binds to free ribosome Endomembrane System Elaborate system of membranes used to make and move proteins in a cell • endomembrane system Oraganelles Used Final Destination of Protein • Rough ER • Outside cell • Vesicles • Within cell membrane • Golgi apparatus • Lysosome • Cell membrane • Lysosome 8 10/5/2015 Endoplasmic Reticulum • Collection of membranous tubes and envelopes • 2 forms • Endoplasmic Reticulum • Rough endoplasmic reticulum (rER rER)) Smooth endoplasmic reticulum (sER (sER)) • Site of lipid synthesis, detoxification • Abundant in liver, kidney, endocrine glands • Gateway to endomembrane system • Studded with ribosomes • Proteins made by ribosomes enter rER through pore • Portion of rER pinches off to encapsulate protein in a transport vesicle Endomembrane System • Some vesicles stay in cytoplasm • Others migrate to the Golgi apparatus Golgi Apparatus Cis face = Receiving face Transport vesicle Trans face = Shipping face Golgi Apparatus • Proteins are modified and/or combined in the Golgi, encapsulated and transported to… 1. Secretory vesicles • Proteins for discharge from cell • Examples: insulin, antibodies Vesicles bound for elsewhere Golgi Apparatus • Proteins are modified and/or combined in the Golgi, encapsulated and transported to… 2. Cell membrane components • Example: glycoproteins 9 10/5/2015 Golgi Apparatus • Proteins are modified and/or combined in the Golgi, encapsulated and transported to… 3. Lysosomes • Cytosolically--active vesicles Cytosolically Lysosomes • Contain more than 50 enzymes • pH of ~4.5 • Break down almost any biomolecule • Cell’s “garbage disposal” • Can fuse with other membranemembrane-defined structures and release contents • Lysosome storage diseases (>30) • Example: TayTay-Sachs disease Endomembrane System Vacuoles • Membranous, fluidfluid-filled sacks • Most cells contain one or more • Animal cells have small ones • Plant cells typically have one large, central one (may have other, small ones as well) Animal Cell Plant Cell Roug h Vacuoles Vacuoles • Play a role in maintaining cell integrity • Regulate cell’s water content central vacuole fills • Example: Paramecia have contractile vacuoles that expel water that leaks in through cell membrane with water to • Example: Plant’s generate turgor pressure 10 10/5/2015 Vacuoles • Storage site in plants • Waste that can’t be excreted • Poisonous compounds • Amino acids, sugars • Pigment (flowers) • Nucleus • Control center of cell • Surrounded by nuclear envelope Makes some plants poisonous, taste bad • Double membrane • Covered with pores • Water, ions pass through freely • Ribosomes stud outer membrane • Continuous with endomembrane system Nucleus • Contains chromatin • DNA and associated Nucleus • mRNA made in nucleus • Exits through nuclear proteins • pores Contains all • Finds ribosomes instructions for • Translated into protein building cell’s proteins • in the cytoplasm Dictates types, amounts of proteins to be made Nucleus • Contains nucleolus • Site of ribosome synthesis Mitochondria • Site of ATP synthesis – “powerhouse of cell” • Double membrane (inner and outer) • Outer membrane is smooth • Inner membrane has deep folds called cristae 11 10/5/2015 Mitochondria • Carry own DNA • Make some of their own protein (contain ribosomes) • Only cellular site to use molecular oxygen Mitochondria • Provide energy = most abundant in cells that need a lot of energy • Compare: sperm vs cartilage Plastids Chloroplasts • Contained ONLY photosynthetic organisms • Highly specialized plastid • Primarily used for storage • Site of photosynthesis • Contains • Pigments (fruit) • Starch • Stroma (fluid) • Thylakoids (membranous sacks) Chloroplasts • Thylakoids contain a pigment called chlorophyll • Gives plants green color • Captures energy from sunlight • Transfers energy to other molecules • Energy used to drive photosynthesis • Sugar is made from CO2 and H2O 12