Transcript Presentation

The A&P of the Cell
The cell
• The smallest living unit.
• Your body consists of billions and billions of
cell that are all working together to keep you
alive.
*The cell theory*
• 1. A cell is the simplest living unit.
• 2. The activity of an organism depends on both
the individual and collective activities of its cell.
• 3. The biochemical activities of cells are dictated
by the relative number of their specific
subcellular structures.
• 4. Continuity of life from one generation to
another has a cellular basis.
The composite/generalized cell
• All cells in the body have generally three main
structures:
– Cytoplasm
– A plasma membrane
– A nucleus
• The exception to this rule is the fully matured
red blood cell, which lacks a nucleus.
Cell Structures:
The plasma membrane
• The plasma membrane is the defining point of a
cell. It separates the inside of the cell from the
outside.
• Another name for the plasma membrane is the
phospholipid bilayer.
The phosopholipid bilayer
• Let’s break down the phrase phospholipid
bilayer.
• Bilayer=
– Bi=two
– Bilayer= two layers
• Phospho=phosphate
• Lipid=fat
• Has a “head” that contains the choline, a
nutrient necessary for building a cell membrane,
and phosphate that causes a change in polarity
on the cell surface. The head is called
“hydrophyllic” because it is designed to touch
water.
• Has a “tail” that is a chain of fatty acids that are
insoluble in water. They are called hydrophobic
because the fatty acids avoid water at all costs.
• Phospholipid bilayer- a two layer lining of
phospholipids that have hydrophyllic “heads”
that touch the inside and outside of the cell, and
a hydrophobic “tail” that creates a barrier that
defines what stays inside and what stays outside
the cell.
Fluid Mosaic model
• Fluid- movable
• Mosaic- Structure made
up of many different
parts.
• Fluid Mosaic Model- a
multitude of different
proteins float in the fluid
bilayer.
Membrane lipids
• Glycolipids-lipids with carbohydrate sugars
attached. Also act as a cell surface marker.
• Transmembrane proteins: Proteins that are in
or on the lipid bilayer. Allows the transport of
substances and information across the
membrane.
• Interior protein network: provides structural
support and helps give membrane its shape.
• Cell surface marker: “self”-recognition.
Creates glycoproteins and glycolipids that give
the cell its own identity.
• Transporters: selective; only lets certain substances through.
• Enzymes: carries out chemical reactions inside the cell
membrane.
• Cell surface receptors: Picks up chemical messages outside of
the cell.
• Glycocalyx: Gives the cell its own “ID” tag.
• Cell adhesion proteins: allows cells to stick together…literally.
• Cytoskeletal attachments: surface proteins that interact with
other cells are often anchored by the cytoskeleton by linking
proteins.
Cholesterol
• Cholesterol is a steroid found in the cell
membrane of all animal cells.
• Cholesterol is needed to maintain the cell
membrane, and can be produced in our
bodies, and retrieved in the food we eat.
Membrane junctions
• Although some cells are considered “freefloaters” inside the body (i.e. rbcs) most cells
have some anchoring mechanism to bind
themselves together and to other surfaces.
Three factors that can bind cells
together.
• 1. Glycoproteins in the glycocalyx act as an
adhesive. (tight junctions)
• 2. Wavy contours of the membranes of adjacent
cells fit together in a tongue-and-groove fashion.
(Desmosomes)
• 3. Special membrane junctions are formed. (Gap
junctions)
Membrane Transport
• Outside of each cell, there is a fluid that is called
interstitial fluid. This fluid, derived from blood,
acts as a nutrient rich soup.
Membrane Transport continued…
• Although there is constantly information and
materials moving back and forth to and from
the cell by the access of a transmembrane
protein, there are certain selective means by
which these materials can enter the cell.
Methods of getting material through
a membrane
• Passive Processes
– Diffusion
– Filtration
• Active Processes
–
–
–
–
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Active
Vesicular trafficking
Endocytosis
Transcytosis
Phagocytosis
Passive Processes
• Diffusion- the tendency of molecules and ions
to move from areas of high concentration to
areas of low concentration.
Simple diffusion
• Nonpolar and lipid soluble substances diffuse
directly through the lipid bilayer. Includes
oxygen, carbon dioxide, and fat soluble vitamins.
• Example: oxygen in blood cells
Facilitated diffusion
• Some molecules are way too large to fit through
a membrane. These molecules, like glucose,
need to either be ferried across by a carrier
molecule, or it needs to be dissolved in a
solution, like water and brought through a
channel.
Facilitated diffusion
Osmosis
• The diffusion of water through a semipermeable
membrane is called osmosis.
• Water can freely move in and out of the cell
through specialized channels called aquaporins.
It is all about homeostasis
• If two solutions have different concentrations of
solutes, then the one with the higher
concentration of solutes is called hypertonic.
• The solution with the lower amount of solutes is
called hypotonic.
• If the two solutions are equal in solutes, it is
called isotonic.
Active Transport
• Primary Active Transport- Sometimes, when we
must maintain a certain concentration gradient
of solutes regardless of the outside environment,
we can expend ATP and use solute “pumps” to
push a certain amount of solutes against a
concentration gradient to maintain a particular
level.
• Example: sodium-potassium pumps
Primary active transport
Secondary active transport
• As ions are built up inside a cell membrane, the
ions that will eventually leak out can be used to
facilitate transport. As these ions are leaking
back down a concentration gradient, they can do
work by taking other solutes with them.
Vesicular trafficking
• Movement of large particles through the cell
membrane through sacs called vesicles.
– Exocytosis-shipping materials out of the cell.
– Endocytosis- bringing materials from outside of the
cell to inside the cell.
phagocytosis
• Also known as “cell eating”
• Phagocytosis is a type of endocytosis that brings
in a large particle for digestion. These vesicles
are usually brought to and combined with a
lysosome that will release enzyme to break down
the larger particle into smaller particles.
Indigestible materials are then kicked out of the
cell through exocytosis.
Pinocytosis
• Pinocytosis is a process by which certain cells
can engulf and incorporate droplets of fluid.
This is a nonselective process.
• i.e.- Cells of the small intestines
The plasma membrane: resting
potential
• Membrane potential= voltage
• All body cells generate at least some resting
potential inside the body. All cells are said to be
polarized because of the -50 to -100 mV resting
potential they have innately.
• The negative sign means the voltage occurs
inside the cell.
Resting potential
• Diffusion causes ionic imbalances that polarize
the membrane, and active transport maintains
that membrane potential.
• Typical ions that are associated with resting
potential: Na+, K++
If you recall
• Earlier we made mention in diffusion that solutes move
down a concentration gradient. This is true for
unpolarized particles and some ions, but not all ions.
• Some ions can hinder diffusion due to the electrical
differences in the potential of the ions and the
membrane of the cell.
• They can also move not only through a chemcial
concentration gradient, but an electrical concentration
gradient.
• In conculsion, some ions are driven not only by
chemical differences, but electrical differences in the
membrane of the cell from which they diffused.
The plasma membrane’s interaction
with the environment
• The glycocalyx is a major player in the cell’s
interaction with the outside.
• Cell membrane can react with biochemicals and
other hormones outside of the cell that may
cause the cell to act or react to the outside
environment differently.
Cell environment interactions
• Cell adhesion molecules- also called CAMs.
Allows cells to anchor themselves to other cells.
(i.e. desmosones) CAMs act as:
– Velcro like molecules that allow attachment to other
cells
– Act as an arm for migrating cells to cling to when
moving through the body.
– SOS signals that rally leukocytes when blood vessels
are damaged.
– Sensors that respond to cell tension synthesis or
degradation of adhesive membrane junctions.
– Intracellular signals that direct cell migration,
proliferation (making others of it’s kind), and
specialization.
Membrane receptors
• Membrane receptors are integral proteins and
glycoproteins that create binding sites on the
cell’s surface.
• Contact signaling- the actual touching of two
cells. The signals given off by the cell tell the
cells how to react with each other. *Vital for the
immune system*
• Chemical signaling- using the membrane
receptors to pick up chemicals that bind
specifically to said membrane receptor. These
chemicals are called ligands.
– Neurotransmitters
– Hormones
– Paracrines
G-protein linked receptors
• Exert effects through a G-protein that usually acts as a
middle man to signal the activation or deactivation of
ion channels or enzymes. This usually causes a
secondary messenger to activate to communicate with
the cell’s metabolic machinery.
• Secondary messengers
– Cyclic AMP
– Ionic calcium
• Both are designed to transfer the phosphate groups of
ATP to other molecules.
NO- Nitric oxide
• Chemical that can cause an array of cell activities
to occur.
• Very tiny and thus can slip in and out of the cell
very easily.
Cytoplasm
• Cellular material between the plasma membrane
and the nucleus. Contains three major pieces:
– Cytosol
– Cytoplasmic organelles
– Inclusions
Cytosol
• A viscous semitransparent fluid that suspends
other cytoplasmic elements. (i.e. organelles,
solutes, etc.)
Inclusions
• Chemicals that may or may not be present
depending on cell type. (Melanin, glycogen
granules)
Cytoplasmic organelles
• Metabolic machinery of the cell. Each organelle
has its own function.
Mitochondria
• Structure:
– Rodlike, double-membrane structures; inner
membrane folded into projections called cristae.
• Function:
– Site of ATP synthesis; powerhouse of the cell.
Ribosome
• Structure:
– Dense particles consisting of two subunits, each
comprised of rRNA and protein. Free or attached
to rough endoplasmic reticulum.
• Function:
– The site of protein synthesis
Rough Endoplasmic reticulum
• Structure:
– Membrane system enclosing a cavity, the cisterna,
and coiling through the cytoplasm. Externally
studded with ribosomes.
• Function:
– Sugar groups are attached to proteins within the
cisternae. Proteins are bound in vesicles for
transport to the Golgi apparatus and other sites.
External face synthesizes phospholipids.
Smooth ER
• Structure:
– Membranous system of sacs and tubules; free of
ribosomes.
• Function:
– Site of lipid and steroids (cholesterol) synthesis, lipid
metabolism, and drug detoxification.
Golgi body
• Structure:
– A sack of smooth membrane sacs and associated
vesicle close to the nucleus.
• Function:
– Packages, modifies and segregates proteins for
secretions from the cell, inclusion in lysosomes, and
incorporation into the plasma membrane.
Lysosomes
• Structure:
– Membranous sac containing acid hydrolases.
• Function:
– Site of intracellular digestion.
Peroxisomes
• Membranous sacs of oxidase enzymes.
• The enzymes detoxify a number of toxic
substances. The most important enzyme
catalase, breaks down hydrogen peroxide.
Cilia
• Structure:
– Short cell-surface projections; each cilium is
composed of nine pairs of microtubules surrounding
a central pair.
• Function:
– Coordinated movement creates a unidirectional
current that propels substances across cell surfaces.
Flagella
• Structure:
– Like cilium. But longer. Only found in sperm cells
in humans.
• Function:
– Propels the cell.
Microvilli
• Structure:
– Tubular extensions of the plasma membrane; a
bundle of actin filaments.
• Function:
– Increase surface area for absorption.
Nucleus
• Structure:
– Largest organelle. Surrounded by the nuclear
envelope; contains fluid nucleoplasm, nucleoli, and
chromatin.
• Function:
– Control center of the cell; responsible for
transmitting genetic information and providing the
instructions for protein synthesis.
Nuclear Envelope
• Structure:
– Double membrane structure pierced by pores, outer
membrane continuous with ER, and is studded with
ribosomes on its surface.
• Function:
– Separates the nucleoplasm from the cytoplasm and
regulates passage of substances to and from the
nucleus.
Nuclear envelope
Nucleoli
• Structure:
– Dense spherical nonmembrane bound bodies that
are composed of ribosomal RNA and proteins.
When you look at a stain of a nucleus, the dark spot
in its center is the nucleoli.
• Function:
– Site of ribosome subunit manufacture.
Chromatin
• Structure:
– Granular. Thread-like material composed of DNA
and histone proteins.
• Function:
– DNA constitutes the genes. Often combine with
histones to form chromosomes.
The cell cycle
• Includes the growth, reproduction and cell
death.
Interphase
• The period in the cell cycle where the cell grows,
replicates its DNA and prepares for mitosis, this
takes up most of the cell cycle.
• Subphases
• G1 phase= 1st subphase, cell growth
• S phase= 2nd subphase, DNA replication
• G2 phase= 3rd subphase, cell prepares for
division.
DNA Replication
• DNA helix is unwound and broken by the
enzyme DNA helicase. The site where the
DNA is being split in two is referred to as the
replication fork.
• Each nucleotide strand serves as a template for
building a new complimentary strand of DNA.
• At the site where new nucleotides attach to the
newly forming strand, an amassing of proteins
and enzymes called a replisome forms.
• At sites where DNA synthesis occurs, there will
be RNA primers that actually start the synthesis.
• When the primer is in place DNA polymerase
starts attaching nucleotides to the old strands,
the leading strand will be continually
synthesized. (3 prime to 5 prime end)
• the lagging strand will need to be put together in
pieces. (5 prime to 3 prime end)
• DNA ligase then fixes any breaks in the sugar
backbone of the new DNA molecule.
• Any errors will then be removed by base
excision repair (BER) and repaired by DNA
polymerase and DNA ligase.
Prophase
• Nucleoli disappears.
• Centrosomes begin to move to opposite ends of
the cell.
• Spindle fibers are beginning to form.
metaphase
• Chromosomes are aligned down the center of
the cell.
• Spindle fibers attach to the centromere located
on each of the chromosomes.
anaphase
• Spindle fibers pull on the chromosomes at the
centromeres.
• Centromeres on each chromosome split
simultaneously.
• The “daughter” chromosomes are pulled to
opposite ends of the cell.
Telophase
• Chromosomes are covered by a newly forming nuclear
envelope.
• The chromosomes are then unwound back into
chromatin.
• The cell membrane begins to pinch into two pieces.
cytokinesis
• The cell membrane completely seals off and two
entirely separate cells are formed.
• The ring where cytokinesis forms is called the
contractile ring and it is composed mostly of
actin microfilaments.
Protein synthesis
• The creation of a protein. Directed by the
genetic code, which occurs by translation of
mRNA into protein via tRNA.
genes
• Genes are segments of DNA that carry
instructions for creating polypeptide chains.
• Polypeptides- a chain of linked amino acids.
Proteins are created by linking polypeptides
together.
• All proteins are polypeptides. Not all
polypeptides are proteins. Meaning that
sometimes more than one polypeptide needs to
be added together to form a functional unit.
When a strand of DNA is read
• The four nucleotide bases A, T, G, and C form
the “words” that create amino acids. Amino
acids are “read” in groups of threes (3). This is
called a triplet and each triplet forms an amino
acid.
• The three nucleotides that are being read are
called a “reading frame”. If the reading frame is
adjusted, the resulting amino acids being created
may change.
In human DNA
• There areas of non-encoding regions called
introns, filled with junk DNA that does not
contain genetic information.
• The regions that contain the encoding regions of
DNA are called exons.
RNA
• It is important to realize that in interphase,
DNA never leaves the nucleus. It is because of
this that a message needs to be sent to the
ribosomes so that they know what proteins to
create.
Transcription
• Involves the transfer of information from a
DNA’s base sequence to a complimentary base
molecule.
• Each gene has three regions that are important
in transcription: The promoter region, the
coding region, and the termination sequence.
RNA polymerase
• An enzyme that is present in the nucleus of the
cell.
• RNA Polymerase reads the DNA and is
responsible for creating the appropriate mRNA
strand.
Promoter region
• Region where the gene acts as a light switch.
• RNA polymerase recognizes that promoter
region and knows to begin transcription there.
• RNA polymerase binds to the promoter region
and the DNA double helix unwinds.
• As RNA polymerase runs down the unzipped
portions of the DNA, it reads one side of the
DNA and creates a complimentary mRNA.
• After the complimentary mRNA is produced, it
breaks free of the DNA and the DNA is folded
back into its helix.
• When RNA polymerase runs into the terminator
sequence, the RNA folds over on itself and the
mRNA stops being produced.
• After that the mRNA and RNA polymerase
break off of the DNA strand.
Spliceosomes
• Remember that our mRNA still has those junky
introns in it, so in order to get rid of them, we
have a special RNA protein complex called
spliceosomes that enter the mRNA and snip out
the introns.
Translation
• In protein synthesis, we take the nucleic acid
sequences we have from mRNA and “translate”
them into tRNA.
• Each triplet in the mRNA base sequence is called a
codon. Since there are four nitrogenous bases, and
three bases per amino acid, you have 64 possible
combinations, and only 20 amino acids.
• This means multiple sequences must code for one
amino acid.
Amino Acid Chart
Once the mRNA is carried out of the
nucleus…
• It is bound to a small ribosomal subunit that is
in the cytoplasm.
• Then tRNA comes into play and starts to bring
the appropriate amino acids to the ribosome.
• tRNA binds the amino acid to the mRNA
through hydrogen bonds and the complimentary
bases that are attached to the mRNA form the
anticodons.
• As each new amino acid is brought to the
ribosome and bound to the mRNA, the old
tRNA is broken off without its amino acid
(which is no attached other amino acids) and is
sent back into the cytoplasm to get more amino
acids.
• Once the “stop” codon on the mRNA sequence
has been reached, the synthesis of the amino
acid sequence halts and the resulting chain of
amino acids is your protein.
Other Roles of DNA
• Antisense RNAs: A piece of a DNA strand that
can intercept the mRNA and bind to it causing
the prevention of protein translation.
• microRNAs: Can silence other parts of RNAs
preventing translation.
• Riboswitches: Acts a switch to turn on/off
protein synthesis in response to certain
environmental conditions.
Transcription and Translation
Animations
• Transcription:
• http://wwwclass.unl.edu/biochem/gp2/m_biology/animati
on/gene/gene_a2.html
• Translation:
• http://vcell.ndsu.edu/animations/translation/m
ovie-flash.htm