THE MOLECULAR BASIS OF INHERITANCE

ANNOUNCEMENTS• Second set of genetics problems has been

posted!!

OBJECTIVES• Know the structure of DNA

• Understand the relationship between genes and proteins

• Be familiar with scientists that contributed to the field of molecular genetics in the early mid 20th century

• Understand relevant vocabulary

THE MOLECULAR NATURE OF

GENESBy early 1900s:

• The fact that chromosomes are responsible for heredity is known

THE MOLECULAR NATURE OF GENES

First Half of 1900s:

– Dominated by research on what genes are composed of and how they work

COMPOSITION OF GENES: DNA

Hershey & Chase (1952):

DETERMINING THE STRUCTURE OF DNA James Watson &

Francis Crick

(1953):

HOW GENES FUNCTION

Beadle &Tatum (1941): :

THE GENETIC CODEHow do we go from DNA to protein?

DNA

RNA

Protein

THE CENTRAL DOGMAFrancis Crick:

THE GENETIC CODEGeorge Gamow:

How manybases specifya singleamino acid?

Since there are only 4 bases, a singlet code could only specify 4 amino acids.

A doublet code couldspecify a maximum of4 x 4 or 16 amino acids.

A triplet code could specify amaximum of 4 x 4 x 4, or 64amino acids.

1 Base? 2 Bases? 3 Bases? 4 Bases?...

4 < 20: Not enough

16 < 20: Not enough 64 > 20: More than enough

1 2 3 4 1 2 3 4

5 6 7 8

9 10 11 12

13 14 15 16

1 2 3 4

5 6 7 8

9 10 11 12

13 14 15etc...

U GC A U

G

C

A

U

G

C

A

U

G

C

A

U

G

C

A

U

G

C

A

U

G

C

A

U

G

C

A

U

C

A

U C A G

U C A G

U C A G

U C A G

U C A G

U C A G

U C A G

U C A

U

G

C

A

U

G

C

A

U

G

C

A

U

C

A

mRNAGC CA

CC

G AGA A AA AA A AA AU U U UU U U U UC CC CC CC CCC C CGG G

GG G

G

G

FOUR RNA BASES (U,C,A,G) MUST SPECIFY 20 AMINO ACIDS

DECIPHERING CODONS Codon:

THE GENETIC CODERecent Work: