Cell Structure

Chapter 3

Looking at Cells

1st microscope invented in the 1600s Robert Hooke (Cork Cells) Scientists use the Metric System or

International Systems of Measurements SI units are based on powers of 10

– μ = micro μm = micrometer

Characteristics of Microscopes

Light Microscope– Light passes

through one or more lenses to produce an enlarged image

Electron Microscope– Forms an image

of a specimens using a beam of electrons rather than light

Characteristics of Microscopes

MAGNIFICATION – is the quality of making an image appear larger than its actual size

RESOLUTION – is the measure of the clarity of an image

Types of Microscopes

Compound Light Microscopes– 2 lenses– Objective Lens (40 X)– Ocular Lens (10 x)

Magnification up to 2000 X View images from 0.5 μm to 0.5 cm Used to view images such as living cells Lower magnification than electron

microscopes

Types of Microscopes

Electron Microscope

– Magnification up to 200,000 X

– Object & electron beam are placed in a vacuum chamber

– Object is stained with metal ions

– Electron beam is absorbed by the ions

– Electrons produce a fluorescent image called the TEM

Types of Microscopes

Scanning Electron Microscope– Electrons bounce off the specimen– Creating a 3-D image

Scanning Tunneling Microscope– Uses needle-like probe to measure

differences in voltage caused by electrons that leak from the surface

– 3-D images– Living organisms can be viewed with this

scope

Section 1 Review 1. How many cm are in a m? 2. What is the difference between

resolution and magnification? 3. What measurement system do

scientists use? 4. Why can living cells not be viewed

under an electron microscope? 5. The English scientist Robert Hooke

used a crude microscope to examine these….

Section 2: Cell Features

Schleiden, Schwann, Virchow CELL THEORY

– 1) All living things are made of one or more cells

– 2) Cells are the basic units of structure and function in organisms

– 3) All cells arise from existing cells

Cell Size

Small cells are more efficient than large cells

All substances that enter or leave a cells have to cross the cell’s surface

Surface area- to- Volume – LOW – substances can not enter or leave

Small cells have a higher surface area- to – volume ratio– Shorter distance to travel

Common Features of Cells

CELL MEMBRANE – encloses the cell– Regulates what enters & leaves the cell

CYTOPLASM – cell’s interior CYTOSKELETON – fibers suspended

in the cytoplasm RIBOSOMES – cellular structures on

which proteins are made DNA – instructions for the cell

Prokaryotes

The smallest and simplest cells Are single-celled organisms Lack a NUCLEUS Examples: Bacteria Reproduce Rapidly Do not need oxygen to survive Some can make their own food

Characteristics of Prokaryotes CYTOPLASM – semi-solid material that

surrounds everything inside the cell– DNA, Ribosomes & enzymes

CELL WALL – surrounds the cell membrane– Function: Provides support &

structure– Found in plants, fungi & some

bacteria– Made of polysaccharides

Characteristics of Prokaryotes

Capsule – surrounds the cell– Cling to lots of things

Flagella – long, threadlike structures that extend from the cell surface– Function: helps the cell move

Eukaryotic Cells Have a Nucleus NUCLEUS – houses the DNA Organelles - internal compartments

– Carry out specific activities in the cell Vesicles – move proteins & other

molecules from cell to cell CILLIA – short hair-like projections

– Functions: Movement & transport of materials across the cell membrane

Eukaryotic Cells

CYTOSOL – fluid material that makes up the cytoplasm

CYTOSKELETON– Made of protein fibers– Function: Holds the cell together– All connected to one another– 3 kinds of fibers – Actin Fibers,

Microtubules & Intermediate Fibers

Cytoskeleton

Actin Fibers – determine the shape Microtubules – act as a highway

system

– Transport info from the nucleus to the rest of the cell

Intermediate Fibers – are an anchor for ribosomes & enzymes

The Cell Membrane

Selective Permeability – Only let certain things enter or exit

Phospholipid = 1 lipid + 2 fatty acids

– Head Polar

• Phosphate Group

• Attracted to water

– 2 Tails NonPolar

• Repel water

The Cell Membrane LIPID BILAYER – double layer of

phospholipids Marker Proteins -- “Name Tags”

– Direct cells to the proper location Receptor Proteins -- “Antenna”

– Receive and transmit info Transport Proteins -- “Locked Door”

– Allow only certain ions and molecules to cross the cell membrane

Enzymes – assist in biochemical reactions

Section 2 Review 1. Describe the importance of surface-

area-to volume ratio of a cell. 2. How are Prokaryotic & Eukaryotic

Cells similar? Different? 3. Describe the function of 2 cell

membrane proteins. 4. What does the cell theory state? 5. What does the term “selectively

permeable” mean in regards to a cell membrane?

Section 3: Cell Organelles Cell functions are controlled by the

NUCLEUS

– Surrounded by the NUCLEAR ENVELOPE• Made up of 2 lipid bilayers• NUCLEAR PORES

–Ribosomal RNA pass through the pores into the cytoplasm

• Ribosomes are partially assembled in the NUCLEOLUS

The Nucleus

DNA stored inside the nucleus Eukaryotic DNA is wound around

proteins CHORMOSOMES – DNA strands

– Humans = 46– Garden Peas = 14

Ribosomes & the ER

RIBOSOMES make protein & RNA– Mobile in the cytoplasm– Stationary on the Rough ER

ENDOPLASMIC RETICULUM– Move proteins & other substances

throughout the cell– Has a membrane that is made up of a lipid

bilayer

Ribosomes & the ER

VESICLE – is a small membrane bound sac that transports substances inside the cell– Separates proteins made on the Rough ER

from proteins made in the cytoplasm SMOOTH ENDOPLASMIC RETICULUM

– Lacks ribosomes– Function: Makes lipids & breaks down toxic

substances

Packaging & Distribution of Proteins

GOLGI APPARATUS– Is a set of flattened, membrane-bound sacs

that package & distribute – Proteins are modified in the GA & enter new

vesicles– Vesicles take the proteins outside the cell

OR– Vesicles remain in the cell & become

LYSOMES • Contain digestive enzymes

Mitochondria

Function: Harvest energy to make ATP Muscle cells can have 100s – 1000s 2 Membranes (Inner & Outer)

– Here chemical reactions produce ATP Also has DNA

– Circular – similar to prokaryotic DNA

Structures of Plant Cells

3 Organelles NOT found in Animal Cells 1) CELL WALL

– Adds additional support, give shape, protects from damage & connects with adjacent cells

2) Chloroplasts– Use light to make carbohydrates from

carbon dioxide and water– Surrounded by 2 layered membrane &

contains DNA

Structures of Plant Cells

3) Central Vacuole– Takes up most of volume – Contains

• Water• Ions• Nutrients• Waste

– When full it makes the cell rigid– Allows the plant to stand upright

Section 3: Review

1. Describe the role of the nucleus in cell activities.

2. Sequence the course of newly made proteins from the rough ER to the outside of the cell.

3. Name 2 organelles a plant has that an animal cells does not.

4. The mitochondria has the nickname “The Powerhouse”. Why is this a good nickname?