BIOL241
Anatomy of the cell:
organelles, cell division, and
the central dogma
SAC Request
• From Audrey Rose Cabinet Coordinator
Student Administrative Council
• SAC is looking for dedicated students to
apply for the Student Cabinet, Fee Board,
Arts & Lectures, and Research &
Advocacy committee positions
• Do you want to get involved? Have good
leadership qualities?
• https://studentleadership.northseattle.edu/
room CC1446. Application deadline: July 10
• Audrey-Rose.Barnes@seattlecolleges.edu
Tutoring Schedule - Summer
Schedule Update
Lab Practical Exams
9 July*
18 July
1 Aug.
15 Aug.
Practical 1: Histology
Practical 2: Bones
Practical 3: Muscles
Practical 4: Nervous
*(was 2 July)
Anatomy of the Cell
Organelles
Question
• A red blood cell is placed in a solution and
a few minutes later, the cell shrinks
(crenates). What was the tonicity of the
solution?
Question
• Celery begins to wilt after it has been in
the fridge for a while. You can actually
restore some of its crispness by
submersing it in a solution. What kind of
solution would you use?
Cellular level
• Cytology: structure and function of cells
• Cell biology
Cell Theory
• Cells are smallest unit of life
• All cells come from previously existing
cells through cell division
• Cells perform all physiological functions
• Homeostasis is maintained at the level of
the cell which impacts the whole
organisms: tissues, organs, and systems
Numbers and diversity
• Body contains trillions of cells
• Also has thousands of different types of cells
(there are hundreds of different types of
neurons alone)
Two general classes of cells
1. Somatic cells (diploid, 2n) – two copies
of each chromosome
2. Sex cells (haploid, n) – one copy of each
chromosome
3. Gametes
Organelles
• Internal cell structures that perform
specific cellular functions
• Cytoplasmic organelles:
– Membranous
• Mitochondria, peroxisomes, lysosomes,
endoplasmic reticulum, and Golgi apparatus
– Nonmembranous
• Cytoskeleton, centrioles, and ribosomes
• Exterior: Plasma membrane
Cytoplasm
• Cytoplasm – material between plasma
membrane and the nucleus
• Cytosol – largely water with dissolved
protein, salts, sugars, and other solutes
Cytoplasm = cytosol + organelles
Anatomy of a Cell
Nonmembranous: Cytoskeleton
• The “skeleton” of the
cell
• Dynamic, elaborate
series of protein rods
running through the
cytosol
• Consists of:
– Microfilaments
– Intermediate filaments
– Microtubules
• Muscle cells contain
thick filaments
Microfilaments
• The smallest in diameter (7nm), most fragile
• Made of the protein actin and located in the
periphery of the cell
• Attached to the cytoplasmic side of the plasma
membrane
– Braces and strengthens
the cell surface
– Involved in cell
movement and shape
changes
Intermediate filaments
• Intermediate in size (7-11nm)
• Tough, insoluble protein fibers with high tensile
strength
• The most durable of the cytoskeletal fibers
• Several varieties exist (e.g. keratin)
• Functions
– Provides shape of the cell
– Resist pulling forces
Thick filaments
• Only found in muscle cells
• Made of protein myosin
• Interact with actin microfilaments to cause
contraction
Microtubules
• Largest of the fibers (25nm)
• Dynamic, hollow tubes made of the spherical protein
tubulin
• Microtubular array of the cell is near the nucleus
• Functions:
– Determine the overall shape of the cell and distribution of
organelles
– Help move structures in the cell (like highways)
– Form the spindle apparatus
– Form centrioles and cilia
Microtubules
Figure 3.24c
Centrioles and Cilia are made
of microtubules
• Centrioles
– Organize mitotic spindle
during mitosis
– Form the bases of cilia
and flagella
• Cilia
– Used to propel material
in one direction across
cell surfaces
– Whip-like, motile cellular
extensions on exposed
surfaces of certain cells
– Move substances
Motor Molecules
• Protein complexes that function in motility
• Powered by ATP
• Attach to receptors on organelles
Cilia
Figure 3.27b
Cilia
Figure 3.27c
Ribosomes are the organelles for
protein synthesis
• Consists of two subunits made
of rRNA and protein
• Site of protein synthesis
• Two kinds of ribosomes found
in cells
– Free ribosomes synthesize
soluble proteins
– Fixed ribosomes synthesize
proteins to be incorporated
into membranes
Membranous organelles
Endoplasmic Reticulum
• Interconnected network
of tubes and parallel
membranes enclosing
cisternae
• Continuous with the
nuclear membrane
• Four major functions
–
–
–
–
Synthesis
Storage
Transport
Detoxification
• Two types of ER
– Smooth ER
– Rough ER
Rough ER
• “ Rough ” because external surface is
studded with fixed ribosomes
• Synthesizes
secreted
and
integral
membrane proteins and may chemically
modify them
• Responsible for the synthesis of
phospholipids for cell membranes
• Also important for shipment of proteins to
the Golgi apparatus
Endoplasmic Reticulum (ER)
Figure 3.18a, c
Smooth ER
• Why is it called smooth?
• Responsible for the synthesis and storage
of lipids and carbohydrates
• Detoxification of drugs and toxins
Very large and developed
in liver cells. Why?
Structure  function
Smooth ER
• Catalyzes the following reactions in
various organs of the body
– In the liver – lipid and cholesterol metabolism,
breakdown of glycogen and, along with the
kidneys, detoxification of drugs
– In the testes – synthesis of steroid-based
hormones
– In the intestinal cells – absorption, synthesis,
and transport of fats
– In skeletal and cardiac muscle – storage and
release of calcium
Golgi Apparatus
• Typically contains 5-6
Stacked and flattened
membranous sacs called
cisternae
• Functions in modification,
concentration, and
packaging of proteins:
– Modifies and packages
secreted proteins
– Packages special
enzymes
• Also renews the cell
membrane (adds lipids)
Golgi Apparatus
• Transport vessels from the
ER fuse with the cis face of
the Golgi apparatus
• Proteins then pass through
the Golgi apparatus to the
trans face
• Secretory vesicles leave the
trans face of the Golgi stack
and move to designated
parts of the cell
Figure 3.20a
Pathways of the Golgi Apparatus
Cisterna
Rough ER
Proteins in cisterna
Phagosome
Membrane
Vesicle
Lysosomes containing acid
hydrolase enzymes
Vesicle incorporated
into plasma membrane
Pathway 3
Coatomer
coat
Golgi
apparatus
Pathway 2
Secretory vesicles
Pathway 1
Plasma membrane
Proteins
Secretion by exocytosis
Extracellular fluid
Figure 3.21
Lysosomes
• Spherical membranous bags containing digestive
enzymes
• Arise by budding off of Golgi
• Digest ingested bacteria, viruses, and toxins
• Degrades and recyles nonfunctional organelles
• Specializations:
– Breakdown glycogen and release thyroid hormones
– Secretory lysosomes are found in white blood cells, immune
cells, and melanocytes
Like a “disposal” for large objects from inside and outside
the cell
Lysosome Functions
Endomembrane System
• System of organelles that function to:
– Produce, store, and export biological
molecules
– Degrade potentially harmful substances
• System includes:
– Nuclear envelope, smooth and rough ER,
lysosomes, vesicles, Golgi apparatus, and the
plasma membrane
Endomembrane System
Figure 3.23
Lysosomal storage diseases
• Tay-Sachs
Lack an enzyme (protein) called
hexosaminidase A (hex A) necessary for
breaking down certain fatty substances in
brain cells called gangliosides (see AM
p.29)
Peroxisomes
• Membranous sacs containing enzymes that detoxify
harmful or toxic substances (which cells have a lot?)
• Breaks down fatty acids and some organic
compounds
• Produced by the division of existing peroxisomes
• Convert free radicals to hydrogen peroxide (H2O2)
• Catalase enzyme coverts H2O2 to H2O and O2
Like a smaller-scale recycler for molecule-sized things
within the cell (cf. lysosome).
Mitochondria
• “Powerhouse” of the
cell…makes most of
the cell’s ATP via
aerobic cellular
respiration
• Double membrane
structure with shelf-like
cristae
Nucleus - structure
• Consists of a double
membrane
• Contains nuclear
envelope, nucleoli, and
chromatin
• Holds the DNA in the
form of chromosomes
• Also has RNA and
enzymes
• Has pores for entry/exit
Nucleus - Functions
• Functions as the gene-containing control
center of the cell
• Contains the genetic library with blueprints
for nearly all cellular proteins
• Regulates gene expression: dictates the
kinds and amounts of proteins to be
synthesized
Nucleus - Contents
Nuclear Envelope
• Selectively permeable double
membrane barrier containing
pores
• Outer membrane is
continuous with the rough ER
and is studded with ribosomes
• Inner membrane is lined with
the nuclear lamina, which
maintains the shape of the
nucleus
• Pores regulates transport of
large molecules into and out
of the nucleus
Nucleolus
• Dark-staining spherical body
(or bodies) within the nucleus
• Site of ribosome production
Nucleus –
Chromatin
• Threadlike strands
of DNA and
histones
• Arranged in
fundamental units
called nucleosomes
• Form condensed,
barlike bodies of
chromosomes when
the nucleus starts to
divide
Figure 3.29
SUMMARY
• Diversity of human cells
• Structures and functions of
membranous and non-membranous
organelles
Anatomy of the Cell
Cell Life Cycle - Mitosis
Cell Cycle
• Interphase
– Growth (G1),
synthesis
(S), growth
(G2)
• Mitotic phase
– Mitosis and
cytokinesis
Figure 3.30
Cell Cycle
• Most of a cell’s life is spent in a
nondividing state (interphase)
– Cell is preparing to divide or performing its
normal cell functions
• During interphase the DNA, is referred to
as chromatin
Interphase
• G0 : cells that cease dividing (often permanently)
– perform specialized cell functions only
• G1 (gap 1): metabolic activity and vigorous growth
– organelle duplication, protein synthesis
• S (synthesis): DNA replication
• G2 (gap 2) : final preparation for division
– finishes protein synthesis and centrioles replicate
G0
Cells that are no longer dividing are said to
be in G0.
Q: What cells can you think of that are in
G0?
Chromosomes
• Humans have 23 pairs; one of each pair comes from
Mom, the other comes from Dad
• The two chromosomes of each pair are called
homologous chromosomes
• Each Chromosome is a long molecule of DNA.
• Each contains thousands of genes arranged in a
single file.
• Each gene is a segment of DNA
• Each gene represents blueprints for a protein
Cell Division - Mitosis
• Necessary for growth and maintenance
of organisms
• Responsible for humans developing from
a single cell to 75 trillion cells
• Mitosis divides duplicated DNA into 2
identical sets of chromosomes:
– DNA coils tightly into chromatids
– chromatids connect at a centromere
Mitosis
• The phases of mitosis are:
– Prophase
– Metaphase
– Anaphase
– Telophase
• Cytokinesis
– Cleavage furrow formed in late anaphase by
contractile ring
– Cytoplasm is pinched into two parts just after
mitosis ends
Mitosis - Overview
Prophase
• Chromatin condenses into chromosomes
• Nucleoli disappear
• Centriole pairs separate and the mitotic
spindle is formed
Prophase
Figure 3.32.3
Metaphase
• Chromosomes with
sister chromatids
cluster at the middle of
the cell with their
centromeres aligned at
the exact center, or
equator, of the cell
called the metaphase
plate
Anaphase
• Centromeres of the
chromosomes split
• Motor proteins in
kinetochores pull one of
each sister chromatids
toward poles
• At this point, each
chromatid is now called
a chromosome
Telophase and
Cytokinesis
• New sets of
chromosomes unwind
into chromatin
• New nuclear membrane
is formed from the
rough ER
• Nucleoli reappear
• Cytokinesis completes
cell division
– Cleavage furrow may be
visable as early as late
anaphase
Mitosis
Control of Cell Division
• Surface-to-volume ratio of cells
• Chemical signals such as growth factors
and hormones
• Contact inhibition
• Cyclins and cyclin-dependent kinases
(Cdks) complexes
Regulation of cell division
• Mitotic Rate and Energy
– slower mitotic rate means longer cell life
– cell division requires energy (ATP)
• Muscle cells, neurons rarely divide
• Exposed cells (skin and digestive tract)
live only days or hours
Nucleus Controls Cell
Structure and Function
• Direct control through synthesis of:
– structural proteins
– secretions (environmental response)
• Indirect control over metabolism through
enzymes
Anatomy of the Cell
Central Dogma
Topics – Central Dogma
• DNA and DNA replication
• Protein synthesis
– RNA
– Transcription (RNA synthesis)
– Translation (protein synthesis)
Deoxyribonucleic acid (DNA) function
• Contains genes which are functional
units of heredity
• Each gene contains the instructions for
making one or more proteins
• Exists in the nucleus as chromatin,
when cell prepares to divide the DNA is
replicated and coiled to form a
chromosome (two chromatids)
• Always found in the nucleus
DNA structure
• The DNA molecule resembles a spiral
ladder called a Double Helix (It is double
stranded)
• Contains alternating sugar/phosphate
backbone attached by covalent bonds and
Nitrogen containing bases (A, T, C, and G)
• Monomers of DNA are called nucleotides.
• Strands run anti-parallel and have
orientation (3’ – 5’)
DNA bases
• There are four different
nitrogenous bases;
1. Adenine (A)
2. Thymine (T)
3. Cytosine (C)
4. Guanine (G)
• DNA bases are
complementary:
A-------T
T-------A
G-------C
C-------G
Held together by
hydrogen bonds
• Complementarity
means given one
strand, you can always
predict the other
KEY CONCEPT
• The nucleus contains chromosomes
• Chromosomes contain DNA
• DNA stores genetic instructions for
proteins
• Proteins determine cell structure and
function
The Central Dogma
• DNA  RNA  Protein
DNA Replication
2. Translation
1. Transcription
DNA Replication
• Copies ALL the DNA in a cell in order to
distribute it into two daughter cells during
cell division
• Occurs only during “S Phase” of mitosis
• Requires the enzyme DNA Polymerase
• Splits the two original DNA strands and
builds new complementary DNA strands to
make two complete and identical sets of
the genetic material
• DNA NEVER LEAVES THE NUCLEUS
DNA Replication
DNA Replication: Product
DNA Template
DNA Complementary
A------------------------T
T------------------------A
G------------------------C
C------------------------G
A-------------------------T
T-------------------------A
Protein Synthesis: from gene to
protein
• DNA serves as master blueprint for protein
synthesis
• Genes are segments of DNA carrying
instructions for a polypeptide chain
• Triplets of nucleotide bases form the
genetic library
• Each triplet specifies coding for an amino
acid
DNA instructions become
proteins in two steps
1. Gene transcribed into mRNA
2. mRNA translated into protein
•
Protein synthesis requires:
– several enzymes
– ribosomes
– 3 types of RNA
Ribonucleic acid (RNA)
• Unlike DNA:
– Single stranded
– Bases are A, C, G, U (instead of T)
– Has ribose sugar instead of deoxyribose
• Like DNA
– Contains alternating sugar/phosphate
backbone attached by covalent bonds
• 3 types
– mRNA - messenger (translated into protein)
– rRNA - ribosomal (makes up most of ribosomes)
– tRNA - transfer (helps in translation from mRNA to protein)
2. Transcription
• The process of making a single strand of
RNA from the DNA code in a gene
– In transcription a complementary RNA strand
is made from the DNA template strand
– Only a short portion of the DNA is “copied”
into RNA – that portion is called a gene
• Requires the enzyme RNA Polymerase to
build the RNA strand
• Finished product called mRNA leaves the
nucleus to be translated into protein in the
cytoplasm
Overview of Transcription
Transcription: Product
DNA
RNA Strand
A------------------U
T------------------A
G------------------C
C------------------G
A------------------U
T------------------A
3. Translation
• aka: Protein Synthesis - the mRNA
strand is “read” by the ribosomes and a
strand of amino acids is made.
• Secreted and integral proteins are made
on the rough ER, those that will stay in the
cytoplasm are made on free ribosomes.
the language of nucleic acids (mRNA) is
“translated” into the language of amino
acids (protein)
How is the language translated?
The Genetic Code
• RNA stores genetic information in sets of
three nucleotides called codons.
• Each codon specifies a particular amino
acid (3 nucleic acid bases = 1 amino acid)
• There are 64 codons and only 20 amino
acids
• An adapter molecule allows mRNA codons
to be read and the proper amino acids to
be put into the growing protein
The “genetic code”
Overview
of Translation
amino acid
anticodon
codon
tRNA
Translation
• mRNA moves into the cytoplasm through a nuclear pore
and is bound by a ribosome (free or fixed)
• Adapter molecule tRNA delivers amino acids to
ribosome
tRNA is like the translator
• Each tRNA has an anticodon that matches and binds to
the codon on the mRNA
• 1 mRNA codon translates to 1 amino acid
• Enzymes in the ribosome join amino acids with peptide
bonds
• Resulting protein has specific sequence of amino acids
(Why important?)
Figure 3–13
KEY CONCEPT
• Genes:
– are functional units of DNA
– contain instructions for 1 or more proteins
• Protein synthesis requires:
– several enzymes
– ribosomes
– 3 types of RNA
Genetic Code
• There are 43 = 64 codons and only 20
amino acids
• 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 does this redundancy exist in the
genetic code?
• What is the consequence of two different
codons coding for the same amino acid?
Mutations
• Mutation is a change in the nucleotide
sequence of a gene:
– can change gene function
• Causes:
– exposure to chemicals
– exposure to radiation
– mistakes during DNA replication
• Mutations can lead to cancer
Mutations
• Changes in the DNA
– May or may not cause a change in the protein
and/or a change in the function of that protein
Can be “silent” mutations
SUMMARY
• Structures and functions of DNA, RNA,
and chromosomes
• Central Dogma: DNA replication,
transcription, translation