Chapter 7: Structure and Function - Summary

"Seeing is believing" - microscopes weren't used until the 1600s

Robert Hooke: Used a microscope to look at cork and coined the term "cells"

One of the First Microscopes: Anton von Leewenhoek. FIRST person to OBSERVE and

DESCRIBE MICROSCOPIC ORGANISMS and LIVING CELLS.

1665, the English Scientist Robert Hooke used a microscope to examine a thin slice of cork and

described it as consisting of "a great many little boxes". It was after his observation that Hook

called what he saw "Cells". They looked like "little boxes" and reminded him of the small rooms

in which monks lived, so he called the "Cells".

1838, German Botanist Matthias Schleiden studied a variety

of PLANTS and concluded that all PLANTS "ARE

COMPOSED OF CELLS".

The next year, German Zoologist Theodor Schwann reported

that ANIMALS are also made of CELLS and proposed a

cellular basis for all life.

1855, German Physician Rudolf Virchow induced the cell

theory:

1. All living things are composed of cells

2. Cells are the basic unit of structure and function

3. new cells come from preexisting cells

CELL DIVERSITY Not all cells are alike. Even cells within the same organism show

Enormous Diversity in Size, Shape, and Internal Organization. Your Body contains at least 200

Different Cell Types.

CELL SIZE A few types of cells are large enough to be seen by the unaided eye. The Female

Egg is the largest cell in the body, and can be seen without the aid of a microscope.

MOST CELLS ARE SMALL FOR TWO REASONS:

A. Cells are limited in size by the RATIO between their Outer Surface Area and Their

Volume. A SMALL CELL HAS MORE SURFACE AREA THAN A LARGE CELL FOR A

GIVEN VOLUME OF CYTOPLASM. This is important because the nutrients, oxygen, and

other materials a cell requires must enter through it surface. As a cell grows larger at some point

its surface area becomes too Small to allow these materials to enter the cell quickly enough to

meet the cell's need.

B. THE CELL'S NUCLEUS (THE BRAIN) CAN ONLY CONTROL A CERTAIN

AMOUNT OF LIVING, ACTIVE CYTOPLASM.

CELL SHAPE

Cells come in a variety of Shapes. -

the shape is determined by its function

INTERNAL ORGANIZATION

Cells contain a variety of Internal Structures

called ORGANELLES. (PERFORMS

SPECIFIC FUNCTIONS FOR THE CELL.)

The entire cell is Surrounded by A THIN

MEMBRANE, called the CELL

MEMBRANE.

A Large Organelle near the

Center of the Cell is the

NUCLEUS. IT CONTAINS THE CELL'S GENETIC INFORMATION

AND CONTROLS THE ACTIVITIES OF THE CELL.

The PRESENCE OR

ABSENCE of a NUCLEUS

is important for Classifying

Cells.

ORGANISMS WHOSE

CELL CONTAIN A

NUCLEUS AND OTHER

MEMBRANE-BOUND

ORGANELLES ARE

CALLED

EUKARYOTES.

ORGANISMS WHOSE CELLS NEVER CONTAIN (OR LACK) A NUCLEUS AND OTHER

MEMBRANE-BOUND ORGANELLES ARE CALLED PROKARYOTES.

UNICELLULAR ORGANISMS such as bacteria and their relatives are Prokaryotes.

All other organisms are Eukaryotes; plants, fish, mammals, insects and humans.

PARTS OF THE EUKARYOTIC CELL

Eukaryotic Cells generally have THREE Main Components: A Cell Membrane, A Nucleus, and

other Organelles.

THE NUCLEUS (plural, Nuclei)

The Nucleus is the CONTROL CENTER (BRAIN) of the

Cell. Most Cells have a Single Nucleus some cells have more

than one. The nucleus is surrounded by a Double Layer

Membrane called the NUCLEAR ENVELOPE. The

Nucleus contains DNA, the HEREDITARY MATERIAL OF

CELLS.

The DNA is in the form of a long Strand called

CHROMATIN. During Cell Division, Chromatin strands

COIL and CONDENSES into thick structures called

CHROMOSOMES.

RIBOSOMES (RIE-buh-SOHMZ)

Ribosomes Are Not Surrounded by a membrane. They are the site of PROTEIN SYNTHESIS

(Production or Construction) in a cell.

ENDOPLASMIC RETICULUM (ER) (EN-doh-PLAZ-mik ri-TIK-yuh-luhm)

The ER is a system of membranous tubules and sacs which act as

an Intracellular Highway, which transports materials through the

cell.

It Can be ROUGH OR SMOOTH.

A. ROUGH ER is studded with RIBOSOMES and processes

PROTEINS to be exported from the cell.

B. SMOOTH ER IS NOT Covered with RIBOSOMES and

processes LIPIDS and CARBOHYDRATES. The Smooth ER is involved in the synthesis of

steroids in gland cells, the regulation of calcium levels in muscle cells, and the breakdown of

toxic substances by liver cells.

CYTOPLASM (SIET-oh-PLAZ-uhm)

EVERYTHING BETWEEN THE CELL MEMBRANE AND THE NUCLEUS IS THE

CELL'S CYTOPLASM.

GOLGI APPARATUS (GOHL-jee)

The Golgi Apparatus is the Processing, Packaging and Secreting

Organelle of the Cell that is made of flattened SAC

.

LYSOSOMES (LIE-suh-sohmez)

Lysosomes are small spherical organellesthat are filled with enzymes. It's function is digestion,

or breakdown of lipids, carbs, and proteins.

VACUOLES The SECOND prominent structure in Plant Cells is the large VACUOLE. The

VACUOLE is a large membrane-bound sac that takes up a large amount of space in most Plant

Cells.

MITOCHONDRIA (MET-oh-KAHN-dree-uh)

Mitochondria are the sites of Chemical Reactions that transfer Energy from

Organic Compounds to ATP (Cellular Respiration). Energy contain in food is

released. Converted to ATP. ATP is the molecule that most Cells use as their

main Energy Currency. THE "POWERHOUSE" OF THE CELL.

PLASTIDS

A common kind of PLASTID is the CHLOROPLAST,

(figure 4-17) an organelle that converts SUNLIGHT,

CARBON DIOXIDE, AND WATER INTO SUGARS. This

process is called PHOTOSYNTHESIS.

CYTOSKELETON In Animal Cells, an internal framework

called CYTOSKELETON maintains the Shape of the Cell

and helps it to move.The CYTOSKELETON consists of

TWO Types of structures: MICROFILAMENTS AND

MICROTUBULES.

CILIA AND FLAGELLA Cilia and Flagella are Hairlike Organelles that extend from the

surface of the cell, where they assist in movement. CILIA ARE SHORT HAIRLIKE

PROJECTIONS. FLAGELLA ARE LONG WHIPLIKE PROJECTIONS.

PLANT CELLS

1. Most of the Organelles and other parts of the cell are common in ALL Eukaryotic Cells. Cell

from different organisms have even greater difference in structure.

2. Plant Cells have Three Additional Structures Not found in animals cells - CELL

WALLS, VACUOLES, AND PLASTIDS that are extremely important to Plant Function.

3. In addition to their unique structures, Plant Cells have: MITOCHONDRIA, RIBOSOMES,

AND the other organelles.

THE CELL MEMBRANE

The Cell Membrane is a complex barrier separating the cell from it's external environment. The

"Selectively Permeable" Membrane regulates what passes into and out of the cell.

All cells, from all organisms, are

surrounded by a CELL MEMBRANE.

Cell Membranes are made mostly of

PHOSPHOLIPID MOLECULES.

(Figure 4-5) Phosphate + Lipid.

Phospholipids are a kind of Lipid that

consists of TWO FATTY ACIDS

(TAILS), and PHOSPHATE GROUP

(HEADS).

The

Phosphate Head is HYDROPHILIC meaning

"WATER LOVING". Because of its hydrophilic

nature, the head of a Phospholipid will orient itself so that it

is as close as possible to water molecules.

The Lipid Tails are HYDROPHOBIC meaning

"WATER-FEARING", the Hydrophobic tails will tend to

orient themselves away from water.

Cell Membranes CONSIST of TWO

Phospholipid LAYERS Called a

LIPID BILAYER. (Figure 4-5)

MEMBRANE PROTEINS (Refer

to Figure 4-5)

Some Proteins are Attached to the surface of

the cell membrane, these are called

PERIPHERAL PROTEINS, and are located

on both the Internal and External Surface.

The Proteins that are Embedded in the Lipid

Bilayer are called INTEGRAL PROTEINS.

Carbhydrates act as "ID" tags for the cells

CELL WALL

One of the most important differences between Plant and Animal CELLS is the Presence of a

CELL WALL IN PLANT CELLS. A Cell Wall DOES NOT REPLACE the Cell Membrane;

Cells with WALLS also have a CELL MEMBRANE. Plant Cells are covered by a Rigid Cell

Wall that lies Outside the Cell Membrane.

PASSIVE TRANSPORT

Cell membranes help organisms maintain Homeostasis by controlling what substances may enter

or leave cells. Some substances can cross the cell membrane without any input of Energy by the

cell. The movement of such substances across the membrane is known as PASSIVE

TRANSPORT.

To stay alive, a CELL MUST EXCHANGE Materials such as Food and Waste With Its

ENVIRONMENT. These materials must cross the Cell Membrane.

DIFFUSION The Simplest type of PASSIVE TRANSPORT, Does Not require the cell to use

Energy, is DIFFUSION. THE MOVEMENT OF MOLECULES FROM AN AREA OF

HIGHER CONCENTRATION TO AN AREA OF LOWER CONCENTRATIONS. This

difference in the Concentration of Molecules across a space is called a CONCENTRATION

GRADIENT.

DIFFUSION ALWAYS

OCCURS DOWN A

CONCENTRATION

GRADIENT, FROM THE

AREA OF GREATER or

HIGHER CONCENTRATION TO THE AREA OF LESS OR LOWER

CONCENTRATION. When the Concentration of the molecules of a Substance is the Same

Throughout a Space, a State of EQUILIBRIUM EXISTS.

OSMOSIS THE PROCESS BY WHICH WATER MOLECULES DIFFUSE ACROSS A

CELL MEMBRANE FROM AN AREA OF HIGHER CONCENTRATION TO AN AREA OF

LOWER CONCENTRATION IS CALLED OSMOSIS. OSMOSIS OCCURS IN

RESPONSE TO THE CONCENTRATION OF SOLUTES DISSOLVED IN WATER.

Water Moves from AREAS of LOW Solute Concentration to

AREAS of HIGH Solute Concentration. Water will cross the

Membrane toward the Higher Solute Concentration until the

Concentration Gradients of BOTH WATER and SOLUTES

EVEN OUT.

11. The Net Direction of Osmosis DEPENDS on the Relative

IN A HYPERTONIC SOLUTION, THE CONCENTRATION OF

SOLUTE MOLECULES OUTSIDE THE CELL IS HIGHER THAN

THE CONCENTRATION OF SOLUTES INSIDE THE CELL

CYTOSOL. WATER DIFFUSES OUT OF THE CELL until

Equilibrium is established. If the cell loses too much water, the cell will

shrivel and shrink. PLASMOLYSIS

16. IN A HYPOTONIC SOLUTION, THE CONCENTRATION OF

SOLUTE MOLECULES OUTSIDE THE CELL IS LOWER THAN

THE CONCENTRATION OF SOLUTES INSIDE THE CELL

CYTOSOL. WATER DIFFUSES INTO THE CELL until Equilibrium

is established. The Flow of water into a cell causes it to

swell.CYTOLYSIS

Plant Cells do not burst because of their Rigid Cell Wall. The pressure

that Water molecules exert against the cell wall is called TURGOR PRESSURE.

IN AN ISOTONIC SOLUTION, THE CONCENTRATION OF

SOLUTES OUTSIDE AND INSIDE THE CELL ARE EQUAL.

FACILITATED DIFFUSION is PASSIVE TRANSPORT across a Membrane requires NO

ENERGY and ALWAYS occurs DOWN A CONCENTRATION GRADIENT.

Some Molecules are CARRIED

across by CARRIER PROTEINS

EMBEDDED IN the Cell

Membrane that CHANGE SHAPE

when Molecules ATTACH to them.

Ex: Glucose into the Cell.

ACTIVE TRANSPORT (USE OF

ENERGY)

In many cases, cells must move materials up their concentrated gradient, from and area of lower

concentration to an area of higher concentration. Such movement of materials is known as

ACTIVE TRANSPORT. Unlike Passive Transport, Active Transport REQUIRES A CELL

TO EXPEND ENERGY (ATP).

CELL MEMBRANE PUMPS Cells often move molecules across the membrane AGAINST a

Concentration Gradient. From an area of LOW Concentration to areas of HIGH Concentration.

Active Transport often involves CARRIER PROTEINS like those in Facilitated Diffusion. The

CARRIER PROTEINS act as PUMPS that USE ENERGY to move IONS and Molecules

across the membrane.

SODIUM-POTASSIUM PUMPS ARE IMPORTANT FOR MUSCLE CONTRACTIONS,

THE TRANSMISSION OF NERVE IMPULSES, AND THE ABSORPTION OF NUTRIENTS.

SODIUM-POTASSIUM PUMPS IN ANIMAL CELLS PUMP SODIUM IONS OUT, AND

POTASSIUM IN, UP THEIR CONCENTRATION GRADIENT.

TYPES OF BULK TRANSPORT, INCLUDING ENDOCYTOSIS,EXOCYTOSIS,

PINOCYTOSIS, AND PHAGOCYTOSIS.

During ENDOCYTOSIS the Cell Membrane (figure 5-7) Folds

into a POUCH that Encloses the Particles that pinches off

INSIDE the Cell to form a VESICLE (membrane-wrapped

bubbles).

PINOCYTOSIS IS SOMETIMES CALLED "CELL DRINKING".

PHAGOCYTOSIS IS LIKE PINOCYTOSIS, EXCEPT THE CELL ENGULFS A FOOD

PARTICLE OR OTHER CELLS INSTEAD OF A DROP OF LIQUID. "CELL EATING"

DURING EXOCYTOSIS, WASTE AND CELL PRODUCTS

LEAVE THE CELL.

Unicellular organisms vs. multicellular organisms

Cell take on specific tasks - cell specialization

Levels of organization

In most Multicellular Organisms, we find the following organization:

Cellular Level: The smallest unit of life capable of carrying out all the functions of living

things.

Tissue Level: A group of cells that performs a specific function in an organism form the

TISSUE.

Organ Level: Several different types of tissue that function together for a specific purpose

form an ORGAN.

Organ System Level: Several organs working together to perform a function make up an

ORGAN SYSTEM. The different organ systems in a multicellular organism interact to carry out

the processes of life

Organismal Level: all organ systems working together to form an organism