CellsBIOLOGY OCTOBER 2014

What are cells?

The basic unit of life. The smallest things that can carry out life processes.

Some organisms are made up of a single cell (Ex. Bacteria and Archaea)

Others are made up of trillions of cells. (larger organisms)

Size of cells

The largest cell in the human body is the ovum, or egg cell. Roughly 1 mm in diameter and just visible to the naked eye

The smallest cell in the human body is the sperm. 60 micrometers (0.002 inches) in length, and not visible to the naked

eye

The longest cells in the human body is the neuron (nerve cell), which can be over a meter long. Links the brain to other parts of the body.

So, how do we see cells?

Microscope Anton van Leeuenhoek

Developed a simple microscope in the 1600s

Several types of modern microscope Compound light microscope

Uses light and lenses to magnify images

These are the ones we’ll be using

Electron microscopes

SEM, TEM, and STM

Read about these in your book.

Magnification

The power of magnification is the product of the magnifications of the individual lenses Eyepiece x objective

An eyepiece with magnification of 10x and an objective lens with magnification of 40x would equal 10 x 40 =400x magnification

1. Ocular Lens (Eyepiece)

This is what you look through to see the image. It contains a lens (usually 10x magnification)

2. Arm

Structural piece Holds the parts of the microscope in the proper places.

THE ARM IS NOT A HANDLE Never carry the microscope by the arm alone.

One hand around the arm, the other hand underneath the base to support it.

Microscopes are very expensive. Use the utmost care when transporting it.

3. Stage

This is the flat portion where you put the slide. A hole in the stage allows light to pass through the slide

4. Course Focus

Moves the stage up and down. Doing so brings the object into focus.

Move it until the image becomes visible. It will still be a bit blurry.

Note about the Course Focus: Using the course focus to try to get a better image could result in the stage moving the slide up into the objective. This could crack the slide and/or objective lens, and could be a VERY expensive mistake.

5. Fine Focus

Makes tiny adjustments to the stage. Once you have found the image, use the fine focus to make it clear.

6. Base

Bottom of the microscope.

Structural and support.

Remember, one hand underneath the base and the other holding the arm.

7. Light Source

A light bulb Sends light through the slide.

8. Diaphragm

Allows you to adjust the mount of light that come through.

9. Slide Clips

Little metal pieces that hold the slide in place. Make sure that the slide is under the clips.

You do not want the slide moving after you have just found the image

10. Objectives

Each is a different lens that magnifies the image. Most microscopes have several of these ranging from 4x to 200x

Begin on the lowest objective to find the image, then increase to zoom it in.

11. Rotating Nosepiece

Holds the objectives Twist to change magnification.

12. Body Tube

Holds eyepiece

The cell theory

Developed with the contributions from 4 scientists (guaranteed matching question!) Robert Hooke

Matthias Schleiden

Theodor Schwann

Rudolf Virchow

Robert Hooke

1600 English scientist

Looked through a microscope at cork (dead oak bark) Noticed small compartments

Called these compartments “cells”

Matthias Schleiden

1800s German Botanist (studied plants)

Observed that all of the plants he saw were made of cells

Theodor Schwann

1800s German physiologist (studied how body works)

Interesting facts: Coined the term “metabolism”

Important cells in the nervous system are named after him (Schwann cells-protect neurons)

Discovered pepsin-the enzyme that breaks down food in the stomach

Through his work, he determined that all animals were made of cells

Rudolf Virchow

1800s German doctor

Interesting facts: First to recognize leukemia cells

Credited in a lot of early cancer research

First person to determine that disease can pass from other animals to humans and vice versa.

Used his research to determine that cells come from other cells.

Types of Cells

Some cells have small, specialized structures called organelles. Each has a specific function for the cell.

Organelle=little organ

Similar to the organs in your body, each of which does some job to keep you functioning, organelles work together to keep the cell functioning.

2 main types of cells Differentiated by whether they have organelles or not.

Prokaryotic Cells

The simpler of the 2 cell types

Lack organelles Prokaryotic means “Before nucleus”

Most unicellular organisms are prokaryotic Bacteria, Archaea

Eukaryotic Cells

Much more complicated

Contain membrane-bound organelles Eukaryotic=“True nucleus”

Most of the organisms you are familiar with Plants, animals, fungi

Mostly multicellular, though some are unicellular

The nucleus controls the cell and contains DNA

The Plasma Membrane

Flexible boundary between the cell and its environment.

Jobs: Provides protection, allows materials to enter and exit the cell Key in homeostasis-process of keeping proper internal conditions

Cell needs nutrients. These are acquired as they pass through the membrane.

Selective Permeability- Membrane allows some materials to enter, while keeping others out. Similar to a screen on a window (lets air in, prevents birds, insects,

etc.)

Some materials, such as water, enter and exit freely.

Other particles can only enter and exit at certain times.

Structure of the Plasma Membrane

Phospholipid bilayer Phospholipids are large molecules of fatty acids

2 parts

Polar head-attracted to water (also a polar molecule)

Nonpolar tail

The head is hydrophilic (attracted to water)

The tail is hydrophobic (avoids water)

This causes the heads and tails to orient in a certain way Water exists outside the cell and inside the cell

Fluid Mosaic Model

Fluid=The cell membrane is fluid, meaning it is constantly moving.

Mosaic=The membrane has a “pattern” Proteins are embedded in the membrane

Proteins do several jobs, including transport and support

Proteins in the Plasma membrane

Transport proteins- move needed materials into and out of the cell

Some proteins help cells to identify chemical signals and each other.

Others in the inner membrane help give the cell support by attaching to internal structures

Eukaryotic Cell Structure

Eukaryotic Cells have many different parts Structures

Organelles

Each portion does something for the cell.

Cellular boundaries

Plasma membrane Job: Protection and selectively allows materials to enter and exit.

Found in: All cells

Cell wall-rigid structure outside the plasma membrane Job: additional support and protection

Found in: Plants, fungi, some protists, and many prokaryotic cells

Cellular Control

Nucleus-control center of the cell Job: Central in formation of proteins, controls the activity of

organelles

Found in: All eukaryotic cells

The nucleus contains the instructions for making proteins Chromatin-strands of DNA

Forms chromosomes

Nucleus also contains an organelle called the nucleolus Makes ribosomes (to be discussed soon)

Cytoplasm

Jelly-like fluid within the cell.

Outside of the nucleus

Suspends the organelles

Found in all cells

Assembly

Endoplasmic Reticulum (E.R.) Job: Site of chemical reations

Found in: Most eukaryotic cells

2 types:

Smooth E.R.

Many biochemical reactions, including production and storage of lipids

Rough E.R.

Similar to Smooth E.R., but studded with ribosomes

Ribosomes Job: Making Proteins

Found in: most eukaryotic cells, and some prokaryotic cells

Can be free-floating in the cytoplasm, or attached to R.E.R.

Sorting and Packaging

Golgi apparatus- Job: Modifies proteins. Sorts them and packages them into organelles

called vesicles.

Found in: Most eukaryotic cells

Vesicles Job: Movement of proteins

Found in: Most eukaryotic cells

Storage and recycling

Vacuoles Job: Storage of materials, including food, water, enzymes

Found in: Most eukaryotic cells and some prokaryotic cells Large one called central vacuole found in plant cells for storage of water.

Plant cells typically have one large one, animal cells have many small ones

Lysosomes Job: Break down materials in a cell, including

food particles,

invaders such as viruses and bacteria

worn out or broken down cell parts

Found in most eukaryotic cells

Energy

Chloroplasts Job: Convert light energy to chemical energy that can be used

Found in: Plant cells and some unicellular organisms

Contain a pigment called chlorophyll, which traps light energy

Mitochondria Job: Transfer energy from food into usable energy

Found in: Most eukaryotic cells

Support

Cytoskeleton Job: Gives cell shape, supports cell, allows some cells to move.

Found in: most eukaryotic cells

Cytoskeleton is made up of 2 main parts:

Microtubules-thin, hollow cylinders made up of protein

Microfilaments- smaller, solid protein fibers

Centrioles Job: assist in cell division

Found in: most eukaryotic cells

Made up of microtubules

Locomotion

Cilia and flagella Some cells, especially unicellular organisms, are capable of

movement

They use cilia and flagella to move around their liquid environment

Cilia-short, hair-like structures

Used similar to rowboat

Cells typically have many of these

Flagella-longer whip-like projections

Used like a motor on a boat.

Cells typically have only 1 or 2