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 64 (or 43) possible nucleotide “triplets” = codons

• 61 codons code for amino acids, 3 act as “start” or “stop” codons marking the beginning or end of a polypeptide

http://www.nature.com/scitable

THE GENETIC CODE

Fig. 10.11

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-animation-691

2064

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 AUG and code for methionine!

• Next, large ribosomal subunit binds

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

GeneticDiversity

• 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 extra-terrestrial 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/321/5891/967

• 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

ACTIVITY

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?

A BC

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

ACTIVITIES

60 min.