Transcript A TOUR OF THE CELL

A TOUR OF THE CELL
All cells have several basic structures in
common
Within the membrane is a semi-fluid
substance, cytoplasm, in which organelles
are found
All cells contain chromosomes, carrying genes
in the form of DNA
All cells have ribosomes
At the boundary of every cell, the plasma
membrane functions as a selective barrier
that allows sufficient passage of oxygen,
nutrients, and wastes
Prokaryotic and eukaryotic cells
differ in size and complexity
Chromosomes of a eukaryotic cell are
found in a membrane-bound organelle
called the nucleus
 The word prokaryotic is from the greek
pro, before, and karyon, kernal, referring
to the nucleus
 The eukaryotic cell (Greek eu, true, and
karyon) has a true nucleus bound by a
nuclear membrane
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Major differences between
prokaryotic and eukaryotic cells
Within the cytoplasm of a eukaryotic cell
are a variety of membrane bound
organelles of specialized form and
function
 These are absent in prokaryotic cells
 Eukaryotic cells are generally much bigger
than prokaryotic cells
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Major differences between
prokaryotic and eukaryotic cells
Venn Diagram
Prokaryotic
Both
Eukaryotic
The nucleus contains most of the genes in
the eukaryotic cell (some genes are
located in the mitochondria and
chloroplasts)
 The nuclear membrane is a double
membrane, each a lipid bilayer with
associated proteins
 Nuclear pores regulate the entry and exit
of certain large macromolecules and
particles

The Nucleus
Within the nucleus is chromatin
 Chromatin consists of DNA and proteins
 The nucleolus functions in ribosome
synthesis
 The nuclear envelope is perforated with
pores
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The Nucleus
Within the nucleolus a special type of RNA
called ribosomal RNA is synthesized and
assembled with proteins imported from
the cytoplasm
 The nucleus directs protein synthesis by
synthesizing messenger RNA (mRNA)
 Once mRNA reaches the cytoplasm, it
translates its genetic message into a
polypeptide (protein)
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The Nucleus
Ribosomes build a cell’s proteins
 Ribosomes carry out protein synthesis
 Ribosomes are composed of two subunits
 Free ribosomes are suspended in the
cytoplasm, while bound ribosomes are
attached to the endoplasmic reticulum

Ribosomes
Ribosomes
Smooth ER lacks ribosomes
 Rough ER appears rough because
ribosomes stud the surface of its
membrane

Endoplasmic Reticulum
Enzymes of the smooth ER are important
to the synthesis of lipids, including oils,
phospholipids, and steriods
 Liver cells store carbohydrate in the form
of glycogen, a polysaccharide
 The hydrolysis of glycogen leads to the
release of glucose from the liver cells,
which is important in the regulation of
sugar concentration in the blood
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Functions of Smooth Endoplasmic
Reticulum
Enzymes of the smooth ER help detoxify
drugs and poisons, especially in enzymes
 Alcohol and many other drugs induce the
proliferation of smooth ER
 This increases the tolerance to the drugs,
meaning higher doses are required to
achieve a particular effect
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Functions of Smooth Endoplasmic
Reticulum
Many types of specialized cells secrete
proteins produced by ribosomes attached
to the rough ER
 Helps make and transport new proteins to
the golgi apparatus or outside the cell
 For example, certain cells in the pancreas
secrete the protein insulin, a hormone,
into the bloodstream
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Functions of Rough Endoplasmic
Reticulum
The Golgi apparatus finishes, sorts, and
ships cell products
 We can think of the Golgi as a center of
manufacturing, warehousing, sorting, and
shipping

Golgi Apparatus
Products of the ER are modified and
stored and then sent to other destinations
 The Golgi apparatus consists of flattened
membranous sacs, cisternae
 Cisternae look like stacks of pita bread
 The two poles of the Golgi stack are
reffered to as the cis face and the trans
face

Golgi Apparatus
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The cis and trans faces act as the receiving
and shipping departments of the Golgi
apparatus
The cis face is usually located near the ER
Transport vesicles move material from the ER
to the Golgi
A vesicle that buds from the ER will add its
membrane and the contents of its cavity to
the cis face by fusing with a Golgi membrane
The trans face gives rise to vesicles, which
pinch off and travel to other sites
Golgi Apparatus
Lysosomes are digestive compartments
 A lysosome is a membrane-bounded sac
of enzymes that the cell uses to digest
macromolecules
 There are lysosomal enzymes that can
hydrolyze proteins, polysaccharides, fats,
and nucleic acids
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Lysosomes
Lysosomes digest (hydrolyze) materials
taken into the cell and recycle materials
 White blood cells ingest bacteria and
viruses and destroys them in the
lysosomes
 Food vacuoles, formed by phagocytosis
(engulfing smaller organisms or other
food particles) fuse with lysosomes,
whose enzymes digest the food
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Lysosomes
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Membrane-bounded sacs
Freshwater protists (eukaryotes) have
contractile vacuoles that pump excess water
out of the cell
Mature plant cells contain a large central
vacuole enclosed by a membrane called the
tonoplast
The plant’s central vacuole is usually the
largest compartment of in a cell,
compromising 80% or more of a mature cell
Functions of the vacuole include storage,
waste disposal, protection, and growth
Vacuoles
Mitochondria are found in nearly all
eukaryotic cells
 The mitochondrion is enclosed by two
membranes, each a phospholipid bilayer
with embedded proteins
 Proteins that function in respiration,
including the enzyme that makes ATP, are
built into the inner membrane
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Mitochondria
Mitochondria are the sites of cellular
respiration, the catabolic process that
generates ATP by extracting energy from
sugar, fats, and other fuels with the help
of oxygen
 Mitochondria contain ribosomes, and also
contain a small amount of DNA
 Mitochondria DNA programs the synthesis
of the proteins made on the organelle’s
own ribosomes
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Mitochondria
The chloroplast is a specialized member of
a family of closely related plant organelles
called plastids
 A plastid’s function depends mostly upon
which pigments are present
 Chloroplasts contain the green pigment
chlorophyll
 Chloroplasts also contain enzymes and
other molecules that function in the
photosynthetic production of sugar
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Chloroplast
Like mitochondria, chloroplasts have two
membranes
 Chloroplasts contain flattened sacs called
thylakoids
 In some regions, thylakoids are stacked
like pancakes; each stack is called a
granum
 The fluid inside the chloroplast is the
stroma, which contains the chloroplast
DNA and ribosomes as well as many
enzymes
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Chloroplast
Plants are encased by cell walls
 The cell wall is one of the features of plant
cells that distinguishes them from animal
cells
 The wall protects the plant cell, maintains
its shape
 Prokaryotes, fungi, and some protists also
have cell walls
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Cell Wall