the molecular basis of inheritance. announcements second set of genetics problems has been posted!!

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: