10/5/2015. Cell Size. Relative Rate of Reaction

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1 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 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, pre-existing existing cell Cell Theory 3. Each new cell arises from the division of another, pre-existing existing cell Bacteria Drosophila 1

2 Two broad categories Prokaryotes Eukaryotes Cell Types Unicellular All cells identical no specialized function Lack nucleus, other membrane-bound bound organelles Example: bacteria Prokaryotes May be unicellular Eukaryotes Examples: yeast, amoebas May be multicellular Eukaryotes Examples: plants, animals Differ greatly in appearance and function 4 basic components in common 1. Plasma membrane Isolation Protection Sensitivity Support Gatekeeper Eukaryotic Cells Differ greatly in appearance and function 4 basic components in common 2. Cytoplasm Material inside the cell but outside the nucleus Eukaryotic Cells Contains the cytosol and organelles 2

3 Differ greatly in appearance and function 4 basic components in common 3. The nucleus Eukaryotic Cells Control center the brain of the cell Contains the DNA Differ greatly in appearance and function 4 basic components in common 4. Organelles Organs of the cell Perform specific functions Some bound by membranes Eukaryotic Cells Everything inside the membrane, except the nucleus A LOT more on the membrane later Includes Cytosol = liquid portion Organelles Cytoplasm Cells are small, but molecules for their chemical reactions are much smaller Utah Genetics Glucose is 10 8 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 3

4 Why prokaryotic cells stay small Eukaryotic cells have found a way around this: membrane-bound bound organelles Serve to concentrate reactants in appropriate compartments Improves cell efficiency This means eukaryotic cells can be larger than prokaryotic cells Still, being small has some advantages Solutes taken into cells through membrane Consider 2 cubes (even though most cells are spherical) Complete the following calculations: Surface Area: length x width x 6 Volume: length x width x height Surface Area/Volume Cell 1 Cell 2 1 µm 2 µm 1 µm 2 µm Which cell has the greater surface area? Which cell has the greater volume? Which cell has the greater ratio of surface area to volume? Volume increases faster than surface area (x 3 vs x 2 ) 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

5 Organelles Cell Membrane Non-membranous Cell wall Cytoskeleton Cellular extensions Microvilli Cilia Flagella Ribosomes Membranous Endomembrane system Vacuoles Double Membrane Nucleus Mitochondria Plastids Chloroplasts All cells are surrounded by a cell membrane Also called a plasma membrane Consists of a bilayer made of mostly phospholipids Critical to cell function Discussed in great detail later Plants, fungi, and bacteria are also have cell walls Animal cells do not Cell Wall All have a cell membrane Cell Membrane Made of polysaccharides secreted through plasma membrane Non-living Exterior to cell Cell Wall Cell walls of adjacent plant cells stuck together with pectin Porous Cell Wall 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

6 Internal protein network of cells Stabilize cell s 3-dimensional shape Guide vesicles Cytoskeleton Microtubules Formed from tubulin subunits 1. Component of cytoskeleton cell shape, anchor organelles Microtubules 2. Intracellular transport with motor proteins Microtubules 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

7 Microfilaments Comparison of Cytoskeletal Proteins Made of actin subunits Associated with cell movement, changes in cell shape Cilia Whip-like Cellular Extensions Move substances in one direction across stationary cells Example: trachea Flagella Cellular Extensions Substantially longer than cilia Only example in human body: sperm Microvilli Cellular Extensions 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

8 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 Bound for cytosol, = binds to free ribosome mrna Final destination of protein somewhere else = mrna/ribosome complex associates with endomembrane system Endomembrane System Elaborate system of membranes used to make and move proteins in a cell Oraganelles Used Rough ER Vesicles Golgi apparatus Cell membrane Lysosome Final Destination of Protein Outside cell Within cell membrane Lysosome 8

9 Collection of membranous tubes and envelopes 2 forms Endoplasmic Reticulum Smooth endoplasmic reticulum (ser) Site of lipid synthesis, detoxification Abundant in liver, kidney, endocrine glands Rough endoplasmic reticulum (rer) Gateway to endomembrane system Endoplasmic Reticulum 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 Golgi Apparatus Some vesicles stay in cytoplasm Others migrate to the Golgi apparatus Cis face = Receiving face Transport vesicle Trans face = Shipping face Vesicles bound for elsewhere Proteins are modified and/or combined in the Golgi, encapsulated and transported to 1. Secretory vesicles Golgi Apparatus Proteins for discharge from cell Examples: insulin, antibodies Golgi Apparatus Proteins are modified and/or combined in the Golgi, encapsulated and transported to 2. Cell membrane components Example: glycoproteins 9

10 Proteins are modified and/or combined in the Golgi, encapsulated and transported to 3. Lysosomes Golgi Apparatus Cytosolically-active active vesicles Contain more than 50 enzymes ph of ~4.5 Lysosomes Break down almost any biomolecule Cell s garbage disposal Can fuse with other membrane-defined structures and release contents Lysosome storage diseases (>30) Example: Tay-Sachs disease Endomembrane System Vacuoles Membranous, fluid-filled 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 Play a role in maintaining cell integrity Regulate cell s water content Example: Paramecia have contractile vacuoles that expel water that leaks in through cell membrane Example: Plant s central vacuole fills with water to generate turgor pressure Vacuoles 10

11 Storage site in plants Waste that can t be excreted Poisonous compounds Makes some plants poisonous, taste bad Amino acids, sugars Pigment (flowers) Vacuoles Control center of cell Nucleus Surrounded by nuclear envelope Double membrane Covered with pores Water, ions pass through freely Ribosomes stud outer membrane Continuous with endomembrane system Contains chromatin Nucleus DNA and associated proteins Contains all instructions for building cell s proteins Dictates types, amounts of proteins to be made mrna made in nucleus Exits through nuclear pores Finds ribosomes Nucleus Translated into protein in the cytoplasm Contains nucleolus Site of ribosome synthesis Nucleus 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

12 Carry own DNA Mitochondria 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 Contained ONLY photosynthetic organisms Primarily used for storage Pigments (fruit) Starch Plastids Highly specialized plastid Site of photosynthesis Contains Stroma (fluid) Chloroplasts 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 CO 2 and H 2 O 12