Cells

How do we look at cells? Most cells are too small to see with the naked eye, so how do we see them? Just how small is too small?

Microscope Power Line

Compound Light Microscope Uses 1 or more lenses to produce enlarged images Allows you to see living cells Magnifies up to 2,000 times

Electron Microscopes Use beams of electrons, similar to your television Can’t see living cells, because specimens are put into a vacuum Magnifies up to 200,000 times 2 types

Transmission Electron Microscope Thin slices stained with metal ions Heavily stained portions absorb electrons Lightly stained portions the electrons pass through, hitting a fluorescent screen and forming an image Black and white images, color added

Scanning Electron Microscope Coated with layer of metal Electrons bounce off onto a fluorescent screen 3-D black and white images, color added

Scanning Tunneling Microscope Uses voltage differences to create digital images Allows you to see individual atoms in 3-D You can see living organisms Magnifies up to 10 million times

Cell Theory All living things are made of one or more cells Cells are the basic units of structure and function in organisms All cells arise from existing cells

What is a cell? All cells have all of the equipment necessary to perform the essential functions of life All cells share several common features There are 2 types of cells

What features do all cells share? Cell membrane—the outer boundary that encloses the cell, protects it from its surroundings, and regulates what leave and enters, including gases, nutrients, and wastes Cytoplasm—the cell interior Ribosomes—the place where proteins are made DNA—provides instructions

What are the two types of cells? Prokaryotes Eukaryotes

Prokaryotes The smallest and simplest cells, 1 – 15 µm Lack a nucleus and other internal compartments Lived at least 3.5 billion years ago An example is a bacteria

Characteristics of Prokaryotes Grow and divide rapidly Some need O2, others don’t Some make their own food No internal compartments, so enzymes and ribosomes move about freely Single, circular strand of DNA Cell wall

Prokaryotic Cell Wall The cell wall is made of polysaccharides with short amino acid chains attached Prokaryotes have to have a cell wall, because they do not have an internal skeleton A prokaryote’s cell wall is to a bacteria as an insect’s exoskeleton is to an ant

Prokaryotes’ Capsules Some prokaryotes have capsules out side of their cell walls Allow them to cling to almost anything, like skin, teeth, and food How would this benefit them?

Flagella Many prokaryotes have flagella, long threadlike structure that protrude from the cell’s surface and enable movement The flagella rotate to propel the prokaryote

Eukaryotes Any organisms whose cells have a nucleus They also have other internal compartments, called organelles Evolved about 1.5 billion years ago

Nucleus, Organelles, and Cytoplasm The nucleus is an internal compartment that houses the cell’s DNA Organelles are other internal structures that carry out specific functions in the cell Cytoplasm is everything inside the cell membrane but outside the nucleus

Flagella and Cilia Cilia are short, hair-like structures that protrude from cell surfaces Flagella and cilia can propel cells or they can move substances across a cell’s surface Cilia in lungs sweep mucus and debris away and in your ears they conduct sound vibrations

Cytoskeleton The cytoskeleton is a web of protein fibers It holds the cell together and keeps cell membranes from collapsing Anchored to cell membrane It links one region to another Anchors nucleus and organelles to fixed locations 3 different kinds—microfilaments, microtubules, and intermediate filaments

Microfilaments Long and slender, made of actin Network beneath cell’s surface that is anchored to the membrane proteins Determines the shape of the cell

Microtubules Hollow tubes of tubulin Within the cytoskeleton, microtubules act as the highway for transportation of information from the nucleus out RNA/protein complexes are transported along the “tracks” of microtubules by motor proteins

Intermediate Filaments Intermediate filaments are thick ropes of protein They make up the frame that allows ribosomes and enzymes to be confined, which allows cells to organize complex metabolic activities efficiently

Cell Membrane Cell membranes are made up of phospholipids, which are a phosphate group and two fatty acids Phospholipids are made up of a polar “head” and two nonpolar “tails” Phospholipids form a phospholipid bilayer

Cell Membrane Cell membranes have selective permeability The lipid bilayer allows lipids and substances that dissolve in lipids to pass through Membrane proteins are also part of the membrane—some are for transport

Cell Membrane There are several types of membrane proteins, including: Marker proteins Transport proteins Enzymes Receptor proteins Proteins move, because phospholipids are constantly in motion

Nucleus Houses most of the DNA, which controls the cell’s functions Surrounded by a double membrane, called the nuclear envelope or nuclear membrane The nuclear envelope is made of two lipid bilayers Why do you think that there are 2?

Nucleus Nuclear pores are small channels through the nuclear envelope What are the pores for? The nucleolus is an area of the nucleus where ribosomes are partially assembled Eukaryotic DNA is tightly wound around proteins, and appears as a dark mass under magnification most of the time

Ribosomes Made up of dozens of proteins and RNA Cells make proteins on ribosomes Some are suspended in the cytosol. These are “free” ribosomes. “Free” ribosomes make proteins that remain in the cell. Proteins that leave the cell are made on ribosomes on the surface of the endoplasmic reticulum

Endoplasmic Reticulum An extensive system of internal membranes that move proteins and other substances through the cell The membrane of ER is a lipid bilayer with embedded proteins

Rough Endoplasmic Reticulum The Rough ER has ribosomes attached It helps transport proteins made on the attached ribosomes The proteins enter the ER and a small, membrane-bound sac, or vesicle, pinches off Proteins made on ribosomes on the rough ER stay separate from proteins made on free ribosomes

Smooth Endoplasmic Reticulum The Smooth Endoplasmic Reticulum lacks ribosomes, so it appears smooth under an electron microscope The smooth ER makes lipids and breaks down toxic substances

Golgi Apparatus A flattened, membrane-bound sac that serves as the packaging and distribution center of the cell Enzymes in the Golgi Apparatus modify proteins from the ER

Lysosomes Lysosomes are small, spherical organelles that contain the cell’s digestive enzymes

Mitochondria Organelle that uses organic compounds to make ATP, the primary energy source of cells Cells with high energy requirements, like muscle cells, may contain hundreds or thousands or mitochondria

Mitochondria The mitochondria has two membranes The outer membrane is smooth The inner membrane is greatly folded, so that it has a lot of surface area The two membranes form two compartments

Mitochondria The mitochondria also contain DNA and ribosomes, because they make some of their own proteins Most mitochondrial proteins are made in the cytosol

Organelles Only Found in Plants Plants have 3 unique organelles Cell wall Chloroplasts Central vacuole

Cell Wall Plants’ cell membranes are surrounded by cell walls Plant cell walls are made of proteins and carbohydrates, including cellulose Helps support and protect the cells Connects cells to one another

Chloroplasts Chloroplasts are organelles that use light to make carbohydrates from CO2 and H2O Found in algae as well as plants Surrounded by 2 membranes Contain their own DNA

Central Vacuole The central vacuole stores water It may contain ions, nutrients, and wastes It makes the cell rigid, when it is full Enables plants to stand upright

Let’s Review We use microscopes to look at cells that are too small to see with the naked eye The Cell Theory What is a cell? What do all cells share? Prokaryotes vs. Eukaryotes Nucleus, Organelles, and Cytoplasm, oh my! What separates plants from other eukaryotes?

The Cell contains Function as Function as Function as Function as Cytoplasm Ribosomes 3. ER & Golgi apparatus 4. 5. structure Support/ 6. Power Plants 1. 2. contains Function as Function as Function as Function as Function as

How did eukaryotes and prokaryotes come to be so different? Lynn Margulis

Margulis’s Other Causal Questions Why do mitochondria and chloroplasts have their own DNA? Why do they have two membranes, when other organelles only have one? Why do these organelles reproduce separately from the rest of the cell?

Endosymbiont Theory Margulis proposed that billions of years ago, eukaryotic cells arose as a combination of different prokaryotic cells The ancestors of mitochondria and chloroplasts were once symbionts living inside larger cells They eventually lost their independence and became organelles

Endosymbiont Theory The theory answered each of Margulis’s questions They have their own DNA and reproduce separately because they were once independent The inner membrane could be a remnant of the old cell membrane and the outer membrane could be the cell’s membrane surrounding the “foreign cell” Further evidence supports Margulis’s Theory

Why aren’t organisms made of a few large cells? The human body is made up of about 100 trillion cells Most of our cells are from 5µm - 20µm in diameter (There are 100 µm in 1 mm)

Surface Area-to-Volume Ratios Calculate the surface area-to-volume ratio of a cube with a side length of 2mm. Calculate the surface area-to-volume ratio of a cube with a side length of 1mm.

Relationship Between Surface Area and Volume Side Length Surface area Volume Surface area : volume ratio 1 mm 6 mm2 1 mm3 6 : 1 2 mm 24 mm2 8 mm3 3 : 1 4 mm 96 mm2 64 mm3 3:2

Why would the surface area to volume ratio be important? How does the flatness of a single-celled Paramecium affect the cell’s surface area-to-volume ratio? How would it affect the cell’s ability to survive?