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Chapter 4

A Tour of the Cell

Katie Heer

on 26 January 2015

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Transcript of Chapter 4

A Tour of the Cell
Chapter 4
Organisms are either
Single-celled, such as most prokaryotes and protists or
Multicelled, such as plants, animals, and most fungi
Light microscopes can be used to explore the structures and functions of cells.

When scientists examine a specimen on a microscope slide
Light passes through the specimen
Lenses enlarge, or magnify, the image
The electron microscope (EM) uses a beam of electrons, which results in better resolving power than the light microscope.

Two kinds of electron microscopes reveal different parts of cells.

Scanning electron microscopes examine cell surfaces. (SEM)

Transmission electron microscopes (TEM) are useful for internal details of cells.
Magnification is an increase in the specimen’s apparent size.
Resolving power is the ability of an optical instrument to show two objects as separate.
Cells were first described in 1665 by Robert Hooke.
The accumulation of scientific evidence led to the cell theory.
All living things are composed of cells.
All cells come from other cells.
The countless cells on earth fall into two categories:
Prokaryotic cells — Bacteria and Archaea
Eukaryotic cells — plants, fungi, and animals
All cells have several basic features.
They are all bound by a thin plasma membrane.
All cells have DNA and ribosomes, tiny structures that build proteins.
Prokaryotic and eukaryotic cells have important differences
Two Types of Cells
Are smaller than eukaryotic cells
Lack internal structures surrounded by membranes
Lack a nucleus
Have a rigid cell wall
Prokaryotic Cells
Only eukaryotic cells have organelles, membrane-bound structures that perform specific functions.
The most important organelle is the nucleus, which houses most of a eukaryotic cell’s DNA.
Eukaryotic Cells
Eukaryotic cells are fundamentally similar.

The region between the nucleus and plasma membrane is the cytoplasm.

The cytoplasm consists of various organelles suspended in fluid.
Unlike animal cells, plant cells have

Protective cell walls
Chloroplasts, which convert light energy to the chemical energy of food
The plasma membrane separates the living cell from its nonliving surroundings.
The membranes of cells are composed mostly of
The lipids belong to a special category called phospholipids.
Phospholipids form a two-layered membrane, the phospholipid bilayer.
Most membranes have specific proteins embedded in the phospholipid bilayer.
These proteins help regulate traffic across the membrane and perform other functions.
Plasma Membrane
The plasma membrane is a fluid mosaic:
Fluid because molecules can move freely past one another
A mosaic because of the diversity of proteins in the membrane
Plant cells have rigid cell walls surrounding the membrane.

Plant cell walls are made of cellulose
Protect the cells
Maintain cell shape
Keep the cells from absorbing too much water
Cell Wall
The nucleus is the chief executive of the cell.
Genes in the nucleus store information necessary to produce proteins.
Proteins do most of the work of the cell.
Structure and Function of the Nucleus
The nucleus is bordered by a double membrane called the nuclear envelope.
Pores in the envelope allow materials to move between the nucleus and cytoplasm.
The nucleus contains a nucleolus where ribosomes are made.
Stored in the nucleus are long DNA molecules and associated proteins that form fibers called chromatin.

Each long chromatin fiber constitutes one chromosome.

The number of chromosomes in a cell depends on the species.
Ribosomes are responsible for protein synthesis.
Ribosome components are made in the nucleolus but assembled in the cytoplasm.
Ribosomes may assemble proteins:
Suspended in the fluid of the cytoplasm or
Attached to the outside of an organelle called the endoplasmic reticulum
The endoplasmic reticulum (ER) is one of the main manufacturing facilities in a cell.
The ER
Produces an enormous variety of molecules
Is composed of smooth and rough ER
Endoplasmic Reticulum
The “rough” in the rough ER is due to ribosomes that stud the outside of the ER membrane.
These ribosomes produce membrane proteins and secretory proteins.
After the rough ER synthesizes a molecule, it packages the molecule into transport vesicles.
Rough Endoplasmic Reticulum
The smooth ER
Lacks surface ribosomes
Produces lipids, including steroids
Helps liver cells detoxify circulating drugs
Smooth Endoplasmic Reticulum
Golgi Apparatus a.k.a. Golgi Body or Golgi Complex
Works in partnership with the ER
Receives, refines, stores, and distributes chemical products of the cell
Golgi Apparatus
A lysosome is a sac of digestive enzymes found in animal cells.
can break down large molecules such as
Nucleic acids

Lysosomes have several types of digestive functions.
Many cells engulf nutrients in tiny cytoplasmic sacs called food vacuoles.

These food vacuoles fuse with lysosomes, exposing food to enzymes to digest the food.
Small molecules from digestion leave the lysosome and nourish the cell.

Lysosomes can also
Destroy harmful bacteria
Break down damaged organelles
Vacuoles are membranous sacs that bud from the
Plasma membrane
Contractile vacuoles of protists pump out excess water in the cell.
Central vacuoles of plants
Store nutrients
Absorb water
May contain pigments or poisons
Most of the living world runs on the energy provided by photosynthesis.
Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar.
Chloroplasts are the organelles that perform photosynthesis.
Chloroplasts have three major compartments:
The space between the two membranes
The stroma, a thick fluid within the chloroplast
The space within grana, the structures that trap light energy and convert it to chemical energy
Mitochondria are the sites of cellular respiration, which produce ATP from the energy of food molecules.

Mitochondria are found in almost all eukaryotic cells.

An envelope of two membranes encloses the mitochondrion.

These consist of
An outer smooth membrane
An inner membrane that has numerous infoldings called cristae
Mitochondria and Chloroplasts
Contain their own DNA, which encodes some of their proteins.
Energy conversion:
Chloroplasts --> Sunlight into Sugar,
Mitochondria --> Sugar into ATP
Double Membrane-Bound Organelles
The cytoskeleton is a network of fibers extending throughout the cytoplasm.

Maintaining Cell Shape
The cytoskeleton
Provides mechanical support to the cell
Maintains its shape
The cytoskeleton contains several types of fibers made from different proteins:
Are straight and hollow
Guide the movement of organelles and chromosomes
Intermediate filaments and microfilaments are thinner and solid.
Cilia and flagella aid in movement.
Flagella propel the cell in a whip-like motion.
Cilia move in a coordinated back-and-forth motion.
Cilia and flagella have the same basic architecture.
Cilia may extend from non-moving cells.
On cells lining the human trachea, cilia help sweep mucus out of the lungs.
CH 4 Question # 13
Now Let's Review
Turn in Your Responses.
Now Let's Go Over the Answers.
1. What type of cell lacks membrane-bound organelles?
2.What type of cell always lacks a cell wall?
3.The cytoskeletal organelle is composed of each of the following structures, except _____.
a.intermediate filaments
4. ER stands for __________ which is series of membranes that extend through the cytoplasm of eukaryotic cells.
a.endo reticulum
b.endocytoplasm reticulum
c.endoplasmic reticulum
d.emergency room
5. The nucleus contains which of the following?
b.endoplasmic reticulum
d.Golgi bodies
a. Prokaryote
d. Animal
b. cilia
c. endoplasmic reticulum
c. DNA
How is the nucleoid region of a prokaryotic cell unlike the nucleus of a eukaryotic cell?
There is no membrane enclosing the prokaryotic nucleoid region.
What is the function of ribosomes?
Protein synthesis
6. Energy, or ATP, is produced in which organelle?
a. nucleus
b. ribosome
c. mitochondria
d. vacuole
c. mitochondria
Cell Organelle
c. mitochondria
Word Roots
plasma = something molded/ molded, plasm
nucle = nucleus
cyto = a cell
chrom = color
bi = two
endo = within, inner
reticul = a network
vesic = bladder
apparat = prepared, a preparation
chloro = green
vacu = empty
skeleto = skeleton
micro = small
cili = small hair
flagell = whip
word root
micro = small
word root
pro= before
eu = true
bacteri = bacteria
archae = ancient
word root
plasma = something molded, molded, plasm
word root
nucle = nucleus
cyto = cell
word root
chrom = color
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