Cells Structure, Function and Homeostasis
Characteristics of Cells Basic unit of life anything alive is made of cells Plasma membrane (skin) that separates them from the environment. Skeletonsfor protection & support (proteins) Move (via proteins) Communicate (via hormones) Harness & use Energy (produce enzymes, heat) Reproduce (maintain & copy blueprint for life)
Cells are small 10 100µm Small to minimize energy needs But large enough to house specialized organelles and to minimize heat loss
Size determines rate of life Large enough to house organelles needed to eat, grow, reproduce Small enough that verylittle energy & time is needed for transport of nutrients & waste Soviet Russia
Simple, Prokaryotic cells Lack nuclei (have nucleoid region), few organelles Circular DNA (with just 1 copy of each gene)
Bacteria & Archaea - Prokaryotes Wildly diverse ~ 500 species in your mouth alone Abundant (numerous) 10 12 on your skin; 10 14 in G. I. tract; 1 teaspoon of soil contains billions Ubiquitous O 2 -free mud; salt flats; boiling hot springs; bedrock 1500 m deep; 10 km beneath ocean s surface; 0-121 C
2/3 major evolutionary lineages
Types of Eukaryotic cells
Eukaryotic Animal cell Endomembrane System Nucleus Smooth & Rough Endoplasmic Reticulum Golgi Apparatus Lysosomes ** Plasma membrane Ribosomes Peroxisomes Mitochondria Centrioles ** Flagellum ** Cytoskeleton
Eukaryotic Plant cell Vacuole Cloroplasts (& other plastids: amyloplasts) Cell wall
Nucleus: Control center (brain) Cytoplasm - organelles, free proteins, ions (guts) Cell (plasma) membrane - barrier between inside and outside (skin)
Questions for the cell What structure controls which proteins, lipids & RNA are produced & when? Where do cells get Energy? Which structures harness it? What structures move stuff around the cell? Where are proteins and lipids built? How do cells move molecules in and out? How do cells eat, drink & defend themselves?
Nucleus: Control center Holds DNA, and machinery for replicating DNA and transcribing it into proteins Surrounded by nuclear envelope (phospholipid bilayer) Nuclear pores Chromatin Chromosomes
Genetic code = DNA, coiled into chromosomes Chromosomes? Hypercoiled chromatin Chromatin? DNA coiled around protein
Where and what is the cytoplasm? Between cell membrane & nuclear membrane Consists of: Cytosol: intracellular fluid (mostly H 2 0, ions & buffering proteins) Organelles: structures with specific functions; suspended in cytosol Inclusions: Insoluble material (e.g. lipids)
Ribosomes Organ of protein synthesis Made of 2 subunits; each made of rrna + protein Two varieties Free ribosomes: produce proteins that travel to nucleus Fixed ribosomes: produce proteins for export to Endoplasmic Reticulum (ER)
Endoplasmic Reticulum (ER) Network of membranes connected to nuclear envelope 4 major functions 1. Synthesis (pro, carbs, lipids) 2. Storage 3. Transport 4. Detoxification Two types 1. Smooth 2. Rough
Smooth ER (SER) Why is it called smooth? Responsible for the synthesis and storage of: Phospholipids and cholesterol for maintenance & growth of cellular membranes (ER, nucleus, Golgi apparatus (GA)) What type of molecules? Steroid hormones: estrogens and androgens Triglycerides in liver and fat cells Glycogen in skeletal muscle and liver cells What type of molecules?
Workshop Site ofprotein synthesis (it has fixed ribosomes!!) Some chemical modification. Polypeptide chains migrate into cisternae, assume tertiary structure + additional modification Ships proteins to GA via transport vesicles Rough ER (RER)
Golgi Apparatus Packing & shipping depot Consists of 5-6 flattened membranous disks (cisternae) Functions Modifies (adds parts) & packages secretions Renews cell membrane Packages special enzymes
Functions of GA Produces 3 type of vesicles: 1. Secretory - exocytosis 2. Membrane renewal replacement & remodeling 3. Lysosomes - Primary contain inactive digestive enzymes
Lysosomes digest!
Show Lysosomes
Abnormal lysosomes Lack, or have malfunctioning enzymes Normal cell products accumulate & stifle (suffocate) cells Tay-Sachs disease Lysosomes lack enzymes that break down lipids in nerve cells Pompe s disease Lysosomes lack hydrolytic enzyme that splits glycogen
The endomembrane system allows membrane flow Phospholipid bilayer is maintained! Nuclear envelope continuous network of SER & RER transport vesicles Golgi Apparatus secretory vesicles cell membrane
Peroxisomes metabolize dangerous material Functions: Absorb and breakdown fatty acids and nucleic acids - produces H 2 O 2 (danger!) Convert free radicals to H 2 O 2 Coverts H 2 O 2 to harmless H 2 O and O 2, using catalase Produced by division of existing peroxisomes Contain digestive enzymes; produced @ free ribosomes
Concept Check The cell is sometimes described as a protein factory. Using the cell-asfactory analogy, which of the following accurately describes the functions of the endomembrane system? a) The ribosomes on the rough endoplasmic reticulum are analogous to a production line in a factory. b) The golgi apparatus is analogous to the packaging and shipping department. c) The nucleus is analogous to management offices. d) All of the above.
Mitochondria = Powerhouse
Mitochondria harness energy! powerhouse of the cell makes ATP Double membrane Number per cell varies with metabolic activity (0% volume of RBC, 20% volume of liver cell) Aerobic respiration Anaerobic resp.
Chloroplasts make food! Photosynthetic organisms (Autotrophs) Sunlight + CO 2 + H 2 0 = sugars Stroma: tubules & membranous disks Grana: stacks of disks; membranes chock full of chlorophyll, which traps solar energy
Cell Membrane = Fluid Mosaic
Structure of cell membrane Contains lipids, proteins and carbohydrates Lipids Phospholipids; Cholesterol; Glycolipids Proteins Integral; Peripheral Carbohydrates Form glycocalyx (identity)
Cell Membrane Functions Physical isolation - separates inner and outer environments Sensory receptor - receptor proteins sense changes in external environment (encrusted with peripheral nerves) Regulates exchange with the environment - membrane channel proteins + carrier proteins Structural support - intercellular protein attachment