molecular structure & function of genetic material professor janaki natalie parikh...
TRANSCRIPT
D.N.A. Structure
• D.N.A.: deoxyribonucleic acid: is a double stranded (dbl helix) polymer of a nucleotides
• Resides in the nucleus (eukaryotes)• Made of 3 molecules:• Phosphate, Sugar &
nitrogenous base
DNA
• 4 bases in D.N.A.:• Adenine, Guanine, Thymine & Cytosine• Rules for pairing bases together:• Adenine Thymine Guanine Cytosine• Our DNA is composed of literally billions of bases!• Genes are long sections (segments) of D.N.A.
D.N.A. Function• 1. D.N.A. can make a copy of itself, handy during?• Mitosis & meiosis• 2. D.N.A. contains the code for protein synthesis,
the manufacture of proteins• Problem, where does protein synthesis take place?• Ribosomes, located? Outside the nucleus. D.N.A.
can’t leave the nucleus. So how does this get done?
R.N.A.
• R.N.A.: ribonucleic acid, single stranded, free floating throughout the cell
• Similar bases, w/ 1 important diffc.• Adenine, Guanine, Uracil & Cytosine• Adenine Uracil Guanine Cytosine• R.N.A assists in completing protein synthesis
Protein Synthesis
• Proteins: polymers as well, but difft. components?• Amino acids. How many are there?• 20 total. Of these 11 are naturally occuring, the
other 9 must be consumed through food, those are known as “essential amino acids” (in kids 10 are essential, 1 loses this status once we produce it)
• How do we get these essential amino acids?• http://www.glisonline.com/aminoacids.php• http://www.all-creatures.org/health/plantfoods.html
Protein Synthesis
• Recall our logistical dilemma?• Making proteins: multi-step task• Cheesy analogy: outside of the
nucleus is the “hood”, the nucleus: gated commty• D.N.A.: Doesn’t kNow About the hood• However, D.N.A.’s cousin, R.N.A. is another story• R.N.A.: Really kNows About the hood
Steps of Protein Synthesis
• 1.transcription: m.R.N.A. enters nucleus, produces a transcript of D.N.A. code (in R.N.A. language)
• Let’s try part of a sequence:• D.N.A. reads: A T A G A G mRNA?• m.R.N.A.: U A U C U C• 2. translation: t.R.N.A. reads the mRNA transcript &
translates the info one codon at a time
Codons & Genetic Code
• Codons: base triplet that codes for an amino acid• Notice: genetic redundancy: more than 1 codon
codes for the same amino acid(we’ll discusssignifcance of this redundancysubsequently)
Protein Synthesis• Back to our 2nd step: mRNA: U A U C U C
tRNA: A U A G A G• Amino acid: Isoleucine, Glutamic Acid
Genetic Redundancy
• Sometimes mistakes occur in this process (mutation)
• Problem: even 1 incorrect base can render a protein useless junk (loss of function)
• Remember genetic redundancy? It’s purpose:• Serves as an built-in security mechanism, reducing
the chance that a base substitution resuls in loss in protein function
Mutations Overview
• Mutagens: accelerate the rate of mutations• Mutations are completely random accidents• Most mutations result in loss in protein function
(junk protein), some are neutral, Rarely: new protein function producted
• (Ecstasy q: http://www.maps.org/media/mtvclarify.html• http://www.shroomery.org/forums/showflat.php/Cat/0/Number/6307333
Mutations
• Point mutations: involve 1 single base– Base substitution: swapping of nucleotide base
• Can possibly be neutral due to genetic redundancy
– Addition or deletion: extra base insert or a base is omitted from correct sequence
• Results in a frameshift mutation (affects multiple amino acids) & can never be neutral
• http://evolution.berkeley.edu/evosite/evo101/IIIC3aTypes.shtml
Chromosomal Mutations
• Chromosomal mutations (macrolesions): occur during meiosis, larger scale of significance since whole chromosome involved
• Nondisjunction: chromosome pair failed to split• http://www.biostudio.com/d_%20Meiosis.htm• http://www.biostudio.com/d_%20Meiotic%20Nondisjunction
%20Meiosis%20II.htm
• Results in a gamete w/ too many, or too few chromosomes
Trisomy & Monosomy
• Trisomy: presence of 3 chromosomes instead of the normal 2 in a homologous pair
• Monosomy: presence of 1 chromosome instead ofthe normal 2 in a homologous pair
• Examples?• Down’s syndrome: trisomy of #21• http://www.ndss.org/PageFiles/2588/Maternal%20Age%20Chart2.png
Syndromes
• Klinefelter’s Syndrome: XXY or XXXY• Turner’s Syndrome: X0• http://www.nichd.nih.gov/health/topics/klinefelter_syndrome.cfm• http://www.merck.com/mmhe/sec23/ch266/ch266b.html
Mutations & Evolutionary Significance
• In order for a mutation to have an evolutionary impact, it must be inheritable (happens in the gametes)
• Next, we’ll examine a specific point mutation that had a major impact on human populations