1. Molecular Structure & Function of Genetic Material
Professor Janaki Natalie Parikh

2. 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

3. 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.

4. 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?

5. 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

6. 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?

7. 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

8. 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

9. 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 discuss
signifcance of
this redundancy
subsequently)

10. 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

11. 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

12. 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:

13. 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

14. Chromosomal Mutations
Chromosomal mutations (macrolesions): occur during meiosis, larger scale of significance since whole chromosome involved
Nondisjunction: chromosome pair failed to split
Results in a gamete w/ too many, or too few chromosomes

15. Trisomy & Monosomy Trisomy: presence of 3 chromosomes
instead of the normal 2 in a
homologous pair
Monosomy: presence of 1 chromosome instead of
the normal 2 in a homologous pair
Examples?
Down’s syndrome: trisomy of #21

16. Syndromes Klinefelter’s Syndrome: XXY or XXXY Turner’s Syndrome: X0

17. 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