Life of the Cell “Society” on a micro-scale

Learning Objectives 1.What are the characteristics that distinguish prokaryotic and eukaryotic cells? Which type of cell is believed to be older (more primitive)? 2.Describe the four characteristics shared by all cells. 3.Describe the structure and function of the various eukaryotic cell organelles. What adaptive advantage(s) is/are associated with having organelles? 4.Describe the theories that describe the origin of membranous organelles in eukaryotic cells.

Smallest unit of life Can survive on its own or has potential to do so Is highly organized for metabolism Senses and responds to environment Has potential to reproduce The Cell: What do we know so far? p. 52

Cellular Diversity in the Human Body A huge population of trillion cells in the adult 200 different types of cells What does cell shape tell you about its function?

Mid 1600s - Robert Hooke observed and described cells in cork Late 1600s - Antony van Leeuwenhoek observed sperm, microorganisms 1820s - Robert Brown observed and named nucleus in plant cells Early Discoveries Visible light has wavelengths of light that are nm. How does this limit our ability to see objects with a light microscope? p.54

An Introduction to Viruses

Why Are Cells So Small? Surface-to-volume ratio The bigger a cell is, the less surface area there is per unit volume Above a certain size, material cannot be moved in or out of cell fast enough p. 53

Structure of Cells Common structures: –Plasma membrane –DNA –Ribosomes –Cytosol Two types: –Prokaryotic –Eukaryotic Is this cell prokaryotic or eukaryotic? Could it be an animal or a plant cell? Explain. p. 52

Main component of all cell membranes Gives the membrane its fluid properties Two layers of phospholipids Cell Membranes: The Phospholipid Bilayer The dense arrangement of phospholipids makes membranes selectively permeable What does this mean? p. 56

Fluid Mosaic Model  Membrane is a mosaic of 1.Phospholipids Responsible for what characteristic of membranes? 2.Glycolipids & Glycoproteins What combination of molecules make up glycolipids and glycoproteins? 3.Cholesterol Found in all cells? 4.Proteins  Most phospholipids and some proteins are fluid, and can move within the membrane p. 56

Identify the 3 types of lipid molecules found in cell membranes: glycolipids, cholesterol and phospholipids. Describe the function(s) of each.

Membrane Proteins Integral vs. Peripheral Proteins See Figure 4.10

Overview of Membrane Proteins

Archaea and Eubacteria DNA is not enclosed in nucleus Generally the smallest, simplest cells No organelles Prokaryotic Cells p. 58

Sympathy for the life of bacteria If you were a bacterium… –You live in a medium which has the viscosity similar to asphalt. –You have a motor for swimming that only runs in two directions… and you can never stop. –While you can “learn”, you every 20 minutes and have to restart your education. –You can have “sex”. However, since you are going 30mph (relative to your size), it is difficult to find each other.

Prokaryotic Cell Structure bacterial flagellum Sex pilus plasma membrane Circular DNA in “nucleoid” region cytosol, with ribosomes Most prokaryotic cells have a cell wall outside the plasma membrane, and many have a thick, jelly-like capsule around the wall. bacterial flagellum Describe the difference(s) between a cell membrane and a cell wall. Can you explain why a cell wall is a necessary adaptation for prokaryotes?

Eukaroytic Cells Functions of a Nucleus: Keeps DNA molecules separated from (potentially damaging) metabolic machinery of cytoplasm Makes it easier to organize DNA and to copy it before parent cell divides into daughter cells What? Where? Who? Have a nucleus and other organelles Tend to be larger, but no more important than prokaryotes! Diverse environments Eukaryotic organisms –Plants –Animals –Protistans –Fungi p. 60

Nuclear Envelope Two outer membranes (lipid bilayers) Pores span bilayer Why are there pores in the nuclear envelope? one of two lipid bilayers (facing nucleoplasm) NUCLEAR ENVELOPE one of two lipid bilayers (facing cytoplasm) nuclear pore (protein complex that spans both lipid bilayers) p. 61

Nucleus vs. Nucleolus Dense mass (one or more) inside nucleus Cluster of RNA and proteins –Materials from which ribosomes are built What is the role of ribosomes? Subunits must pass through nuclear pores to reach cytoplasm Nucleolus disappears during cell division Why? Chromatin = cell’s collection of DNA and associated proteins w/in the nucleus Chromosome = one DNA molecule and its associated proteins Appearance of nucleus changes as cell divides Figure from: micro.magnet.fsu.edu/cells/nucleus/nucleolus.html micro.magnet.fsu.edu/cells/nucleus/nucleolus.html

Endomembrane System Group of related organelles in which membrane materials are assembled, modified, and shared Endoplasmic reticulum Golgi bodies Vesicles Products are sorted, labeled, and shipped to destination –Export from cell –Insertion into cell membranes p. 62

Rough ER Arranged into flattened sacs Ribosomes on surface give it a “rough” appearance Some polypeptide chains enter rough ER and are modified Cells that specialize in secreting proteins have lots of rough ER Where else do you find ribosomes?

Smooth ER A series of interconnected tubules No ribosomes on surface Lipids assembled inside tubules Smooth ER contains enzymes, and may store some cell chemicals. –Smooth ER of liver inactivates wastes, drugs –Sarcoplasmic reticulum of muscle is specialized to store Ca +2

Golgi Bodies Put finishing touches on proteins and lipids that arrive from ER Package finished material for shipment to final destinations Material arrives and leaves in vesicles –Lysosomes digestive enzymes pumps in H + ions for acidic internal pH –Peroxisomes Enzymes breakdown hydrogen peroxide (H 2 O 2 )

Central Vacuole Single membrane organelle As cell grows, expansion of vacuole as a result of hydrostatic pressure forces a weakened cell wall to expand In mature cell, central vacuole takes up percent of cell interior What happens if you don’t water your plants? Stores amino acids, sugars, wastes (including alkaloids: nicotine, cocaine, caffeine, ephedrine, morphine, heroin codeine, theobromine, & quinine.)

Mitochondria Double membrane organelle –central cavity filled with matrix –inner membrane folds = cristae large surface area for chemical reactions of cellular respiration Function –efficient generation of ATP –“powerhouse of cell” Mitochondria self-replicate –increase in # when need for ATP increases –circular DNA with 37 genes –only inherited from mother (in egg) p. 64

Chloroplasts Convert sunlight energy to ATP through photosynthesis Notice the larger surface area created by thylakoid discs. What chemicals are found embedded in these membranes? The fluid-filled portion of the chloroplast is called stroma.

Origin of Membranous Organelles? No fossil record recording the origin of eukaryotes, however… Both mitochondria and chloroplasts resemble bacteria: –Similar in size –Reproduce by binary fission –Have own DNA, RNA, and ribosomes All eukaryotes share same characteristics: –Cytoskeleton made of microtubules (tubulin protein) and actin –DNA in chromosomes –Membrane-bound organelles

Two Theories for the Origin of Eukaryotes Endosymbiosis Autogenous The Autogenous theory may explain the origin of ____, and the Endosymbiotic theory may explain the origin of ____. p. 294

Length of microtubules or microfilaments can change Parallel rows of microtubules or microfilaments actively slide in a specific direction Microtubules or microfilaments can shunt organelles to different parts of cell (see video) Mechanisms of Intracellular Movement p. 66 Which human cells change their shape dramatically with conscious control?

Plant Cell Features Compare and contrast plant and prokaryotic cell walls. What other eukaryotic organisms produce a cell wall? p. 65

Animal Cell Features p. 65