Cell Structure Chapter 3

3.1 Looking at Cells 1600’s the microscope was invented Robert Hooke 1665 looked at cork and saw little boxes he called “cells”

Anton Van Leeuwenhoek later looked at pond water and saw tiny animals he called “animalcules”

Measuring Cell Structures Based on metric system giga- mega- kilo- hecto- deka- BASE deci- centi- milli- micro- nano- Giga = G Mega = M Micro = µ Nano = n

Characteristics of Microscopes Light Microscope – light passes through 1 or more lenses Electron Microscope – image made by beams of electrons Micrograph – image from a microscope Labeled with what kind of microscope and magnification value Magnification – how many times larger it appears Resolution – measure of clarity Electron Micrograph Ebola Virus 160,000 x magnification

Types of Microscopes Compound Light Microscope 2 lenses with light bulb shining through slide Objective lens in close to slide Ocular lens is near eye 40x x 10x = 400x magnification Third lens hurts resolution Most powerful = 2,000x See something 0.5 µm in diameter 40 x 400 x

Electron Microscope Up to 200,000x Beam and specimen must be in vacuum so e- don’t bounce off gas (no living things) Transmission Electron Microscope Stained with metal ions Very thin slices of specimen Internal structures Black and white but computers add color Scanning Electron Microscope Specimen coated with thin layer of metal 3-D cell surface Artificial color

Scanning Tunneling Microscope Needlelike probe measures differences in voltage caused by e- that tunnel from surface of object 3-D image Used on living things

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

Cell Size Smaller is more efficient Everything must cross cells surface Surface area to volume ratio Too low - substances cannot enter and leave in large enough numbers Small cells have a high ratio

Common Features of Cells Cell Membrane Outer boundary enclosing cell that separates interior Controls flow in and out Cytoplasm Cell interior

Cytoskeleton System of microscopic fibers Act as support structures

Ribosomes DNA Where proteins are made All cells have it Protein instructions Regulate cellular activities Allows for reproduction

Prokaryotes Smallest, simplest, single-celled organism No nucleus (and other parts missing) Cannot carry out many special functions due to missing parts Around at least 3.5 billion years ago (bya) Nearly 2 bya were only organisms on earth Very small from 1 – 15 µm Bacteria Subset that causes infection and food spoiling

Characteristics Large range of environments Many grow and divide rapidly Some don’t need oxygen, others can’t have it Some make own food

Everything inside cell membrane is in cytoplasm Enzymes and ribosomes free to move around Singular, circular DNA located in center Cell Wall – surround membrane Provides structure and support No cytoskeleton so cell wall gives shape Cell wall made of polysaccharides connected by short amino acid chains Some cell walls surrounded by capsule = polysaccharides (allows them to cling to many things)

Flagella – long, threadlike structures that provide movement

Eukaryotic Cells Internal compartments Evolved about 2.5 bya Have an internal compartment for DNA = nucleus Have structures that carry out specific activities = organelles Cytoplasm = everything inside membrane but outside nucleus Membranes connect organelles and provide channels Form envelopes called vesicles that move proteins between organelles

Flagella Cilia Cytoskeleton – short, hair-like structures Used for cell movement or movement of materials over cell Cytoskeleton Protein fibers Holds cell together, keeps it from collapsing Cytosol – fluid surrounding organelles, internal membranes and cytoskeleton

The Cytoskeleton Interior framework of animal cell Protein fibers anchored to inside of plasma membrane 3 kinds of fibers Actin Fibers Long, slender microfilaments Made of the protein actin Determine shape of animal cells Microtubules Hollow tubes Made of protein tubulin Highway for transport from nucleus to parts of cell Intermediate fibers Thick ropes of protein Frame for ribosomes and enzymes keeping them in certain locations

The Cell Membrane Fluid, like a soap bubble Lipids form a barrier allowing only certain things through - selective permeability Phospholipid = 2 fatty acids and a phosphate group Polar head – phosphate group; attracted to H20 2 nonpolar fatty acid tails; repelled by H20 Phospholipids are in a double layer so called the lipid bilayer Allows lipids and nonpolar substances to pass through

Membrane Proteins Proteins are made of amino acids Some are polar and some are nonpolar Some move around Marker proteins attached to carbohydrate tell what kind of cell it is (liver, heart) Receptor proteins bind specific substances (signal molecules) Enzymes in cell membrane important in biochemical reactions Transport Proteins help move things in and out

3.3 Cell Organelles Nucleus Controls most cell functions Surrounded by nuclear envelope Double membrane (two lipid bilayers) Nuclear pores = small channels allow passage through Nucleolus – ribosomes partially assembled here Most DNA stored here Wound around proteins but in elongated thin strands When about to divide they become more compact into chromosomes and form dense rod shaped structures Number of chromosomes depends on species Humans = 46 Peas = 14

Ribosomes and Endoplasmic Reticulum Ribososmes Where proteins are made Made of dozens of different proteins and RNA May be free in cytosol but proteins made there stay in cell

Production of Proteins Endoplasmic Reticulum is a system of internal membranes that move proteins and other structures through the cell It is a lipid bilayer with embedded proteins Rough ER Attached ribosomes Proteins made enter ER Pinched off and form vesicles Keep separate Smooth ER No ribosomes Make lipids Break down toxic substances

Packaging and Distribution of Proteins Vesicles go from ER to Golgi Apparatus Golgi Apparatus Flattened membrane-bound sacs Enzymes inside modify proteins Modified proteins repackaged by GA and bud off Lysosomes – vesicle that contains digestive enzymes

Steps of Protein packaging and distribution Ribosomes on Rough ER make proteins and they are packaged Go from ER to GA In the GA proteins are modified and repackaged Many vesicles move to cell membrane and release cargo Other vesicles remain in cell and go a job

Mitochondria Harvests energy from organic compounds to make ATP which is used as energy by cell Most ATP is made here Cells that use ATP have lots of mitochondria 2 membranes Outer = smooth Inner = folded; large surface area Forms 2 compartments

Mitochondrial DNA DNA and ribosomes make their own proteins though most come from cytosol Mitochondrial DNA (mDNA) is independent from nuclear DNA, similar to circular DNA of prokaryotic cell Believe prokaryotes were ancestors to mitochondria

Structure of Plant Cells Cell Wall Surrounds cell membrane Made of proteins and carbohydrates (cellulose) Helps support and maintain shape Protection Connects to other cells

Chloroplasts Use light to make carbohydrates from CO2 and H20 Along with mitochondria supplies much of energy needed to power cell 2 membranes Contain their own DNA (ancient prokaryotes)

Central Vacuole Stores water May contain ions, nutrients, or wastes When full, cell is rigid