Chapter 7 – Cell Structure
Section 7.1 – Introduction to Cells
Cells are the machinery that allows living things to obtrain and use energy, to respond to their
envirnoment, and to reproduce. All cells have the same basic structure.
How were they discovered?
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1665 - Robert Hooke looked at a slice of cork.
Saw "little boxes" and called them "cells".
Microscope observations of organisms led to the discovery of the basic characteristics
commom to all living things.
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1675 - Anton von Leeuwenhoek first to observe pond water under a microscope and
discovered many living creatures that he called amimalcules, or “tiny animals.”
Over next 150 years, many scientists studied the cells. These discoveries led to the cell theory.
Cell Theory - 3 parts
1.) All living things are composed of 1 or more cells.
2.) In organisms, cells are basic units of structure and function.
3.) Cells are produced only from existing cells.
Looking at Cells
A cell’s shape reflects the cell’s function. There are at least 200 types of cells and the human
body is made up of about 100 trillion cells. Which leads us to the conclusion that cells must be
small!
Cells….
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Must be able to exchange materials in and out of cell.
Must distribute materials within the cell.
Must be efficient. Efficiency depends on ratio of surface area to volume. Smaller cells are
more efficient.
Cell Features
All cells have a cell membrane, cytoplasm, ribosomes, and DNA.
1.) Cell membrane - (plasma membrane)
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Separates the cell's insides from the material outside the cell.
Regulates what moves in and out of the cell.
Necessary for life.
2.) Cytoplasm - Everything inside the cell except the cell's genetic make-up (DNA)
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cytosol - fluid portion
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Many ribosomes are found here.
3.) Ribosomes - structures on which proteins are made
All cells can reproduce!
All cells have genetic material (DNA)
2 Types of cells:
Prokaryotes - single-celled organisms that lack internal membrane-bound compartments
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Simple orgainization
The genetic material is a sinle loop of DNA, which usually lies near the middle of the cell.
Cell wall that surrounds the cell membrane and that provides structure and support.
Some have flagella or cilia to help them move around.
Some of pili that help them stick to other cells like velcro.
Scientists believe that the first prokaryotes may have lived 2.5 billion years ago.
Make up a very large and diverse group of cells.
Eukaryotes – has a nucleus and membrane bound organelles
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Have a true nucleus - membrane bound compartment that houses DNA.
Have organelles that carry out specific functions.
All multlicellular organisms are made up of eukaryotic cells.
Nucleus –
Organelles –
Section 7.2 – Inside the Eukaryotic Cell
Each cell has many compartments that are divided by membranes that make little areas for
specific structures.
The Framework of the Cell
The outside of the cell is bound by a cell membrane.
- Framework called a cytoskeleton is located in the cell. It supports the cell much like bones
support the body. It helps move, keep its shape, and organize its parts.
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There are three kinds of cytoskeleton fibers. They are microfilaments, microtubules, and
intermediate fibers.
Directing Cell Activity
Almost all cell activities depend on the proteins the cell makes. This is done by instructions from
the DNA inside the nucleus. This is why the nucleus runs the cell! The instructions are then
copied by RNA to send messages on how to assemble the proteins.
Nucleus
- Has nuclear envelope with pores (holes)
- Contains DNA
- Has nucleolus that makes ribosome parts. These parts are put together outside the nucleus
Ribosomes
- Made of RNA and proteins
- Make proteins to be used in or outside the cell
 Free ribosomes = proteins used inside
 Bound ribosomes = proteins used outside
 These are put in a package called a vesicle
Protein Processing
Vescile – is a small, often spherical-shaped sac that is formed by a membrane
Two structures are respondsible for modifying, packaging, and transporting proteins that are used
outside the cell. They are the endoplasmic reticulum and the Golgi apparatus.
Endoplamic reticulum (ER) – series of membranes that moves proteins and other substances
through the cell
Endoplasmic Reticulum (ER):
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Moves proteins through the cell.
There are 2 kinds of ER.
2 kinds:
* Rough ER - has ribosomes on it!
- Looks rough!
- Makes and packages proteins to go to the gogli apparatus
*Smooth ER - no ribosomes
- Makes lipids and breaks down toxic substances
Golgi Apparatus (GA) – a set of flattened membrance-bound sacs
Golgi Apparatus (GA)
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Modifies, sorts, and packages cell products
When finished, the package leaves the GA and often leaves the cell
Storage and Maintenance
Vesicles help maintain homeostasis by storing and releasing various substances as the cell needs
them.
Lysosomes:
- Vesicle that has enzymes to break down large molecules.
- Recycles old, damaged, or unused organelles
Vacuoles:
- Large spaces for storage
- Plants have large central vacuoles for water storage
Vacuole – a fluid-filled vescile found in the cytoplasm of plant cells
Energy Production
The energy for cellular functions is produced by chemical reactions that occur in the
mitochondria and chloroplasts. These reaction produce ATP, a form of energy that fules almost
all cell processes.
Chloroplasts:
- PLANTS ONLY!!
- Uses light energy to make sugar
Chloroplasts – an organelle found in plant and algea cells where photosynthesis takes place
Mitochondria:
- Powerhouse of the cell - like a battery!
- Makes ATP - energy currency, remember?
Mitochondria – surrounded by two membranes that is the site of cellular respiration
Section 7.3 – From Cell to Organism
Diversity in Cells
Different cells have different organelles and features that make them what they are.
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Prokaryotes have flagella. Flagella are long threadlike structures that rotate to move.
They also have pili. Pili are short thick outgrowths that allows them to attach to surfaces or
other cells.
Levels of Organization
Plants and animals have many highly speciallized cells that are arranged into tissues,
organs, and organ systems.
We can order cells into different levels of organization:
1.) Tissues - group of cells with similar structures and functions
Ex: muscle tissue
2.) Organs – different tissues come together to make an organ that has a specialized structure
and function
Ex: heart - made of muscle, nerve and other
tissues
3.) Organ systems - organs working together with major body functions
Ex: circulatory system - made of heart, blood
vessels, and blood
Body Types
Some organisms are not complex and some are.
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Some may only have one cell as their whole body.
Some live OK on their own
Others live together and rely on each other for survival. They are called colonial
organisms. Bacteria do this!
Colonial organisms – cells that live as a connected group but depend on each other for survival
Only eukaryotes have true multicellularity (more than one cell).
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They come from one cell that divides and then those cells differentiate, or become
specialized.