Lecture Topics
• Protein Synthesis
• Mitosis
• Epithelial Tissue
Nucleus
• Most cells have one nucleus.
Nucleus
• Exceptions:
• Skeletal muscle cells are multinucleated.
• Some cardiac muscle cells are
binucleated.
• Mature rbc lack a nucleus.
Nucleus
• Nuclear envelope – a double membrane
that surrounds the nucleus
Nucleus
• Both layers of the membrane are lipid
bilayers
Nucleus
• Contains a dark spherical body called a
nucleoli where rRNA are made.
Nucleus
• The nucleoli assembles rRNA and proteins
into ribosomes.
Nucleus
• Ribosomes are exported into the cytosol
and play a major role in protein synthesis
(translation).
Nucleus
• Contains chromsomes. Humans have 46.
Nucleus
• 23 pairs of chromosomes
• 23 from mother
• 23 from father
Nucleus
• All chromsomes are referred to as
autosomes except one pair. In other
words 22 of the pairs are autosomes.
Nucleus
• The last or 23rd pair are referred to as the
sex chromsomes.
Nucleus
• The two chromosomes of each pair are
called homologous chromosomes
Nucleus
• Each Chromosome is a long molecule of
DNA.
Nucleus
• Each Chromosomes contain thousands of
genes arranged in a single file.
Nucleus
• Each gene is a segment of DNA
Nucleus
• Each gene represents a protein
Nucleus
• The DNA molecule resembles a spiral
ladder called a double Helix.
Nucleus
• Monomers of DNA are called nucleotides.
Nucleus
• Each monomer or unit of DNA contains a
1. pentose sugar
2. phosphate group,
3. nitrogenous base.
Nucleus
•
1.
2.
3.
4.
There are four different nitrogenous
bases;
Adenine
Thymine
Cytosine
Guanine
Nucleus
• Cytosine always pairs with Guanine
Nucleus
• Thymine always pairs with Adenine
Nucleus
• These bases are held together by
hydrogen bonds.
Nucleus
DNA Template
A
T
G
C
A
T
DNA Complementary
T
A
C
G
T
A
Protein Synthesis
• Two major Parts
• 1. Transcription (takes place in nucleus)
• 2. Translation ( takes place in ribosomes
in the cytosol)
Protein Synthesis
• Basic order:
DNA → mRNA → Protein
Protein Synthesis: Transcription
• DNA molecules have a template strand
and a complementary strand.
Transcription
• In transcription an RNA strand is made
from the DNA template strand.
Transcription
• There are three different types of RNA that
are transcribed; mRNA, rRNA, tRNA
Transcription
• RNA molecules are single stranded unlike
DNA molecules
Protein Synthesis: Transcription
• At the beginning of a gene there is a DNA
sequence called a promoter.
Transcription
• This promoter tells RNA polymerase
where to start transcription. RNA
polymerase catalyzes transcription
Transcription
• As the DNA molecule unzips, bases pair
with the template strand of the DNA
molecule and a complementary RNA
strand is formed.
Protein Synthesis: Transcription
• RNA have adenine, guanine, and cytosine
bases, but do not have thymine. Instead
they have uracil.
Transcription
• Cytosine, Guanine, and Thymine in the
DNA template pair with Guanine, Cytosine,
and Adenine in the RNA strand.
Transcription
• Adenine in the DNA template pairs with
uracil not thymine in RNA
Protein Synthesis: Transcription
DNA Template
A
T
G
C
A
T
RNA Strand
U
A
C
G
U
A
Protein Synthesis: Nucleus
DNA Template
A
T
G
C
A
T
DNA Complementary
T
A
C
G
T
A
Protein Synthesis: Transcription
• The terminator is a nucleotide sequence
that specifies the end of the gene.
Transcription
• RNA polymerase detaches itself from the
transcribed RNA molecule and DNA
strand.
Transcription
• The transcribed mRNA molecule is
referred to as pre mRNA.
Transcription
• A DNA segment is a gene
Transcription
• Genes codes for proteins
• DNA segment or Gene → RNA → Protein
Transcription
• Not all parts of a gene code for a protein.
Transcription
• A gene can be divided into introns and
exons.
Transcription
• Introns are the parts that don’t code for a
protein.
Transcription
• Exons are the parts that do code for a
protein.
Transcription
• Pre mRNA contains exons and introns
Protein Synthesis: Transcription
• Introns are removed from the pre mRNA
and the exons are spliced together by
small nuclear ribonucleoproteins
(snRNPs).
Transcription
• The end product is a mRNA molecule that
exits the nucleus through a nuclear pore.
Transcription
• The mRNA travels through the cytosol until
it reaches a ribosome where translation
takes place.
Question
• Why do introns exist if it is useless
informaiton?
Question
• If there are only 35,000 to 45,000 genes,
why are there actually 500,000 to 1 million
genes?
Protein Synthesis: Translation
• RNA stores genetic information in sets of
three nucleotides called codons.
Protein Synthesis: Translation
• Each codon specifies a particular amino
acid.
Translation
• There are 64 codons and only 20 amino
acids.
Translation
• This means there are more than one
codon for each amino acid. In other
words, several codons specify for the
same amino acid.
Question
Why this redundancy?
Six Steps in Translation
1. The mRNA molecule binds to the small
ribosomal subunit at the mRNA binding
site.
Translation
1. Then the initiator tRNA that contains the
anticodon attaches to the mRNA codon.
Translation
1. The tRNA contains the amino acid that
corresponds to the codon.
Translation
1. The first codon of an mRNA strand is
always AUG, therefore methionine is
always the first amino acid in a protein.
Translation Steps Cont.
2. The large ribosomal subunit attaches to
the small ribosomal subunit-mRNA
complex, creating a functional ribosome.
Translation
2. The initiator tRNA, with the amino acid
methionine, are now in the P site of the
ribosome.
Translation
3. Now another tRNA with another amino
acid attach to the second mRNA codon
at the A site of the ribosome.
Translation Steps Cont.
4. A component of the large ribosomal
subunit catalyzes the formation of a
peptide bond between methionine in the
P site and the amino acid at the A site.
Translation
4. Then methionine detaches itself from the
tRNA at the P site.
Translation
5. The tRNA at the P site leaves.
Translation
5. The ribosome shifts the mRNA strand by
one codon. Now the tRNA that was in the
A site is now in the P site.
Translation
5. This allows another tRNA with an amino
acid to attach to the codon at the A site.
Steps 3 through 5 occur repeatedly.
Translation Steps Cont.
6. Protein synthesis stops when the
ribosome reaches a stop codon at the A
site.
Translation
6. When a ribosome reaches a termination
codon on the mRNA, the A site of the
ribosome accepts a protein called a
release factor instead of tRNA
Translation
6. Release factor hydrolyzes the bond
between the tRNA in the P site and last
a.a. of the protein.
Translation
6. Then the completed protein detaches
from the final tRNA.
Translation
6. After the tRNA leaves the P site the
ribosome disassociates into small and
large subunits.
DNA Viruses
• In a DNA virus the, the virus uses the host
cells machinery to replicate itself.
DNA Viruses
• The virus is made up of a protein capsid
with viral DNA inside.
DNA Viruses
• It uses the host cells machinery and
duplicates the DNA and makes new
protein capsids via protein synthesis.
RNA Viruses
• In RNA retroviruses like HIV, it is a little
different from DNA viruses but same
concept. It uses the host cell’s machinery
to replicate itself.
RNA Viruses
• The virus is made up of viral RNA
surrounded by a protein capsid.
RNA Viruses
• It forms a complementary DNA strand via
reverse transcriptase.
RNA Viruses
• After the DNA forms double strands, it
then replicates more viral RNA via
transcription
RNA Viruses
• It also makes more capsid proteins via
translation.
10 minute Break
Cell Division
• Interphase
• Mitosis
• Cytokinesis
Interphase
• Our cells are in interphase 90% of the
time.
Interphase
• During this time the DNA, protein, and
RNA are referred to as chromatin.
Interphase
• The chromatin looks like a diffuse granular
mass.
Interphase
• There are three phases of interphase.
3 Stages of Interphase
1. G1 phase
During this phase it duplicates most of its
organelles.
3 Stages of Interphase
2. S phase
Chromosomes duplicate during this
stage. The duplicated chromosomes are
attached at the centromere are referred
to as chromatids.
3 Stages Cont.
3. G2
Cell growth continues and enzymes and
other proteins are synthesized.
* Some cells for example remain in the
G1 stage forever for example nerve cells.
They are said to be in the G0 stage
4 Stages of Mitosis
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
Prophase
• Chromatin fibers condense and are now
visible underneath the microscope as
individual chromosomes.
Prophase
• The chromosomes have been replicated
and are attached to its double or sister
chromatid by the centromere.
Prophase
• Later in prophase mitotic spindle radiating
from the centrioles attach to the
kinetochore ( a protein complex outside
the centromere).
Prophase Cont.
• Nucleoli disappears
• Nuclear envelope disappears as well
Metaphase
• The mitotic spindle aligns the centromeres
of the chromatid pairs at the metaphase
plate.
Anaphase
• The centromeres split separting the two
members of each chromatid pair, which
move toward opposite poles of the cell.
Anaphase
• Once separated, the chromatids are
termed chromosomes.
Anaphase
• The chromosomes appear V shaped
because the centromeres lead the way as
they are being pulled by the mitotic
spindle.
Telophase
• Most events are opposite of prophase
Telophase
• Chromosome revert back to a chromatin
like appearance.
Telophase
• Nuclear envelope develops around each
set of chromosomes.
Telophase
• Nucleoli reappears
Telophase
• Mitotic spindle disappears
Telophase
• Cleavage furrow appears
Cyokinesis
• The cytoplasm, organelles and the two
nuclei are divided into two daughter cells.
Tissues
•
•
•
•
Epithelial Tissue
Connective Tissue
Muscle Tissue
Nervous Tissue
Epithelial Tissue
• Covers the external body surface
(epidermis), lines cavities and tubules, and
generally marks off our insides from our
outsides
Epithelial Tissue
• Contain cell junctions
Epithelial Tissue
• Avascular
Epithelial Tissue
• Contains nerve supply
Epithelial Tissue
• High rate of mitotic division
Cell junctions
• They are contact points between the cell
membranes of tissue cells.
• Five types:
Tight Junctions
Adherens Junctions
Desmosomes
Hemidesmosomes
Gap Junctions
Tight Junctions
• This prevents the passage of substances
between cells.
Adherens Junctions
• Helps epithelial surfaces resist separation
Desmosomes
• Contribute to stability
• Prevent epidermal cells from separating
under tension and cardiac muscle cells
from pulling apart during contraction.
Hemidesmosomes
• Anchor cells
Gap Junctions
• Allows cells in tissues to communicate
Epithelial Cell Surfaces
1. Apical Surface – Faces the body
surface, a body cavity, the lumen, or a
tubular duct
Epithelial Cell Surfaces
2. Lateral surfaces - Face adjacent cells.
Contain cell junctions except
hemidesmosomes
Epithelial Cell Surfaces
3. Basal surface - Opposite of apical
surface. Attaches to the basal lamina of
the basement membrane, an
extracellular layer
Types of Epithelial Tissue
1.
2.
3.
4.
5.
6.
7.
Simple Squamous
Simple Cuboidal
Simple Columnar
Ciliated Simple Columnar
Stratified Squamous
Stratified Cuboidal
Stratified Columnar
Types Cont.
8. Transitional
9. Pseudostratified columnar
Simple Squamous
• Single layer of cells
• Scale like
Simple Squamous
• Functions in filtration, diffusion, osmosis,
and secretion
Simple Squamous
• Lines heart, blood vessels, air sacs,
glomerular capsule of kidneys, serous
membranes
Simple Cuboidal
• Single layer
• Cube Shaped
Simple Cuboidal
• Function in secretion and absorption
Simple Cuboidal
• Covers surface of ovary, lines kidney
tubules and small ducts of glands (thyroid
and pancreas)
Simple Columnar epithelium
• Single layer
• Rectangular shaped
• Some contain goblet cells
Simple Columnar epithelium
• Function in secretion and absorption
Simple Columnar epithelium
• Lines G.I. tract from stomach to the anus,
gallbladder
Ciliated Simple Columnar
•
•
•
•
Single layer
Columnar shaped
Some contains goblet cells
Ciliated
Ciliated Simple Columnar
• Function in moving mucus and other
substances
Ciliated Simple Columnar
• Uterine tubes, uterus, central canal of
spinal cord
Stratified Squamous
• Several Layers
• Scale like shaped
Stratified Squamous
• Function in protection
Stratified Squamous
• Superficial layer of the skin, lining of the
mouth, esophagus, epiglottis, vagina, and
tongue
Stratified Cuboidal
• Several layers
• Square or cube shaped in apical layer
Stratified Cuboidal
• Function in protection and some secretion
and absorption
Stratified Cuboidal
• Ducts of sweat glands, esophageal
glands, and male urethra
Stratified Columnar
• Several Layers
• Rectangular shaped in apical layer
Stratified Columnar
• Function in protection and secretion
Stratified Columnar
• Part of urethra, large excretory ducts of
some glands (esophageal)
Transitional Epithelium
• Several layer
• Scale to cube shaped
Transitional Epithelium
• Function in permitting distention
Transitional Epithelium
• Lines urinary bladders and portions of
ureters and urethra
Pseudostratified Columnar
• Not stratified
Pseudostratified Columnar
• ciliated
Pseudostratified Columnar
• Nucleus of cells are at different levels, all
cells are attached to a basement
membrane, but not all reach the surface
Pseudostratified Columnar
• Function in secretion and movement of
mucus
Pseudostratified Columnar
• Trachea, epididymis, and part of male
urethra
END