FLOW OF GENETIC INFORMATION FROM
DNA  RNA  PROTEIN
• Central dogma
• OH, and by the
way, proteins
make up 75% of
the solids in the
human body!
GENOTYPE
PHENOTYPE
•
DNA specifies synthesis of
proteins in 2 stages:
1. Transcription
- the transfer of genetic info
from DNA  RNA molecule
2. Translation
- the transfer of info from
RNA  protein
THE GENE
•
Unit of heredity with a specific
nucleotide sequence that occupies a
specific location on a chromosome
•
E.g. Map of human chromosome 17
showing a breast cancer gene (BRCA-1)
• Humans have two copies of BRCA-1
which normally suppresses breast
cancer
• If one copy is defective, then no back
up if other gene damaged by exposure
to environmental carcinogens
• Inheriting a defective BRCA-1 gene 
 risk of breast cancer
THE LANGUAGE OF NUCLEIC ACIDS
•
For DNA, the alphabet is the linear sequence of
nucleotide bases
• A single DNA molecule may contain 1000’s of genes
• A typical gene consists of 1000’s of nucleotides
Relative Genome Sizes
http://en.wikipedia.org/wiki/File:Genome_Sizes.png
TRANSCRIPTION OF DNA
•
DNA’s nucleotide sequence “rewritten” into RNA nucleotide
sequence (remember that both are nucleic acids)
•
RNA is made from the DNA template, using a process resembling
DNA replication except
• T’s are substituted by U’s
• RNA nucleotides are
linked by RNA polymerase
UNPACKING TRANSCRIPTION
• Three phases
• Initiation
• RNA elongation
• Termination
INITIATION OF TRANSCRIPTION
• “Start transcribing” signal is nucleotide sequence,
called a promoter
• Located at beginning of gene
• RNA polymerase attaches to the promoter (via
transcription factor)
• RNA synthesis begins
RNA ELONGATION
•
RNA grows longer
•
RNA strand peels away from the DNA template
TERMINATION OF TRANSCRIPTION
• RNA polymerase reaches specific nucleotide
sequence, called a terminator
• Polymerase detaches from RNA
• DNA strands rejoin
PROCESSING OF EUKARYOTIC RNA
•
Unlike prokaryotes, eukaryotes process their RNA
• Add a cap & tail - xtra nucleotides at ends of RNA transcript for
protection (against cellular enzymes) & recognition (by ribosomes
later on)
- Removing introns –
stretches of noncoding
nucleotides that interrupt
coding stretches = the
exons
- Splicing exons together to
form messenger RNA
(mRNA)
TRANSLATION
• Conversion from nucleic acid language to protein language
• Requires
• mRNA
• ATP
• Enzymes
• Ribosomes
• Transfer RNA
(tRNA)
THE GENETIC CODE
•
Shared by ALL organisms
•
The set of rules that relates mRNA nucleotide sequence to amino
acid sequence
•
Since there are 4 nucleotides, there are
nucleotide “triplets” =
•
61 codons code for amino acids, 3 act as “start” or “stop” codons
marking the beginning or end of a polypeptide
(or 43) possible
http://www.nature.com/scitable
Fig. 10.11
THE GENETIC CODE
tRNA
•
Acts as molecular interpreter – decodes mRNA codons into a protein
•
Each codon (thus amino acid) is recognized by a specific tRNA
•
Has an anticodon – recognizes & decodes an mRNA codon
•
Has amino acid attachment site
•
When tRNA recognizes & binds
•
to its corresponding codon in
•
ribosome, tRNA transfers its
•
amino acid to the end of the
•
growing amino acid chain
RIBOSOMES
• Organelles that
• coordinate functions of mRNA & tRNA during translation
• contain ribosomal RNA (rRNA)
UNPACKING TRANSLATION
•
Occurs in the ribosome
•
Like transcription, broken down into 3 phases
•Initiation
•Elongation
•Termination
•
Short but sweet translation animation
• http://www.nature.com/scitable/content/translation-animation6912064
INITIATION OF TRANSLATION
•
Small ribosomal subunit binds to start of the mRNA sequence
•
Then, initiator tRNA carrying the amino acid methionine binds to the
start codon of mRNA
• Start codons in all mRNA molecules are
methionine!
• Next, large ribosomal subunit binds
and code for
POLYPEPTIDE ELONGATION
•
Large ribosomal unit binds each successive tRNA w/ its attached
amino acid
•
Ribosome continues to translate each codon
•
Each corresponding amino acid is added to growing chain and linked
via peptide bonds
•
Elongation continues until all codons are read.
TERMINATION OF TRANSLATION
• Occurs when ribosome reaches stop codon (UAA, UAG, &
UGA)
• No tRNA molecules can recognize these codons, so
ribosome recognizes that translation is complete.
• New protein released
• Translation complex dismantles
•
into its subunits
TERMINATION OF TRANSLATION
• sdf
Fig. 10.20
• Transcription & translation are how genes control
• structures
• activities of cells
• In other words,
FORM & FUNCTION of proteins!
DAY 5: CELL STRUCTURE & FUNCTION
IMSS BIOLOGY ~ SUMMER 2011
MAJOR CATEGORIES OF CELLS
• Prokaryotic cells (the prokaryotes) – vast spp diversity &
abundance !!!
• Domain Archaea - all
• Domain Bacteria -all
• Eukaryotic cells (the eukaryotes)
• Domain Eukarya - mostly
Genetic
Diversity
• Microbes make
up most of
Earth’s genetic
diversity
• This “tree of
life” is like a
map of genetic
relatedness
• Distance (line
length) 
genetic
relatedness
Norm Pace, U. Colorado
THREE-DOMAIN CLASSIFICATION SYSTEM
• Bacteria &
Archaea diverged
very early in
evolutionary
history
• Archaea more
closely related to
Eukarya
PROKARYOTIC VS. EUKARYOTIC CELLS
EXTREMOPHILES &
THE SEARCH FOR LIFE BEYOND EARTH
•
We’ve found prokaryotes in virtually EVERY place
on Earth, even the most unlikely (extreme) places
•Extremophiles: organisms that live in “extreme”
environments
• Scientists are studying these microbes for a better
idea of life’s capacities AND the potential of extraterrestrial life
NASA AND MICROBES
• Microbes @ NASA
• Loads of research, e.g.
• Extremophiles
• How life evolved on Earth
• Biomedical applications
• Modes of virulence & pathogenesis
MONO LAKE BACTERIA: RECENT DISCOVERY
• Oremland & Kulp, USGS, Science (2008)
• https://www.sciencemag.org/cgi/content/abstract/321/58
91/967
• First e.g. of photoautotroph that also uses arsenic
to “fix” CO2
• Microbial arsenic metabolism may extend back to
primordial Earth
RIO TINTO, SPAIN
• 5,000 yrs. of mining activity
• Extreme acidity
• Extreme heavy metal
concentrations
• Surprisingly more
eukaryote than
prokaryote diversity
“On Earth, microbial communities thrive in highly acidic waters rich in iron and sulfur,
such as the blood-red waters of the Rio Tinto in southwestern Spain. Among the
minerals dissolved in the Rio Tinto is jarosite, an iron- and sulfur-bearing mineral also
found on Mars.” -- http://amesnews.arc.nasa.gov/releases/2003/03_74AR.html
A BACTERIAL SUPERHERO
•
Deionococcus radiodurans
•
Found to “beat the constraints” for survival on
Mars (R. Richmond et al., NASA’s Marshall Space
Flight Center)
• Radiation
• Cold
• Vacuum
• Oxidative damage
CORE PRINCIPLE
The cell
•
Basic unit of life
•
Multicellular organisms are organized structures made
up of different cells
•
•
•
Ea. cell shares common properties w/ other cells
Ea. cell has some specialized structures & functions
Cell size (& function) is limited by surface area (SA) to
volume (V) relationships
• SA/V Relationship – Tory Brady
min.
What is the functional significance of this relationship?
Which cell shape would be best in places where rapid
exchange of substances (via diffusion) is a high priority?
C
A
B
SA/V RATIOS
• Can be applied to
• single cells (including single-celled
organisms)
• Important when considering
transport mechanisms and cell
size limitations
• whole animals
• Important when considering
metabolic and
thermoregulatory principles
SMALL INTESTINE (SI) HISTOLOGY
• Form follows
function: SI
microanatomy
important to
understanding its
function
• SI completes
digestion of food, and
most of all nutrient
absorption occurs
here !!!
• Structure of intestinal
mucosa allows for a
600x greater luminal
surface area than if it
had a flat surface
•Intestinal folds  3x 
in SA
•Villi  10x  in SA
•Microvilli  20x  in
SA
THE SCALE OF LIFE
• How can we “see” the tiniest
organisms (or their
components)?
• The unaided human eye is
limited to ~0.1 mm
• How can we see things smaller
than this?
m
m
.
m
• We need to use microscopy to magnify & resolve very tiny
objects to > 1 mm in order to “see” them
http://www.cellsalive.com/howbig.htm
KEY FACTORS OF MICROSCOPY
• Magnification
• How much larger object
appears w/ microscope lenses
than w/out
• Resolution
• Amount of detail (ability to
distinguish between 2 pts. on
an image)
http://homepages.gac.edu/~cellab/chpts/chpt1/intro1.html
MICROSCOPY - OVERVIEW
• Many types for different levels of detail
LIGHT MICROSCOPES
• Most widely used & available
• Basic anatomy
• Total magnification = eyepiece
lens power x objective lens
power
http://www.under-microscope.com/
MICROSCOPY - RESOURCES
• Thorough coverage of the various types of microscopy,
how they work, & their functions
• http://www.cas.muohio.edu/~meicenrd/ANATOMY/Ch1_Microscopy/microscopy.html
• More basic descriptions of microscope types along with an
excellent photo/video library
• http://www.under-microscope.com/
• Cells alive – Termite Guts – Tory Brady
• Tools of the trade – microscopy
• Digital microscopy in the classroom – Sandi Yellenberg
60 min.