Genetics Lecture 10 - Code of Life

Griffith’s Experiment (1928)

Showed bacteria can exchange genetic information by transformation.

S Strain

Lethal, has a protective polysaccharide coat.

R Strain

Non-lethal, lacks protective coat

Transforming Principle

Material from dead S cells that converted R cells; later identified as DNA.

The _____ strain is lethal because of a polysaccharide coat.

S

The S strain is lethal because of a _____ coat.

polysaccharide

Mice injected with R strain live cells _____

lived

Mice injected with heat-killed S strain _____.

lived

Mice injected with live R strain + heat-killed S strain _____ and live _____ strain were recovered from their bloodstream.

died; S

Griffith concluded that R cells were changed into S cells by a _____ principle.

transforming

What did Avery, MacLeod, & McCarty do in 1944?

They repeated Griffith’s experiment using extracts of heat-killed S strain Streptococcus pneumoniae and systematically destroyed different components to identify the transforming principle.

Why did scientists originally expect protein to be the genetic material?

Because chromosomes are made of both DNA and protein, and proteins were thought to be more complex and functional than DNA.

What was the experimental approach in Avery, MacLeod, & McCarty’s study?

They selectively destroyed polysaccharides, lipids, RNA, proteins, or DNA in the S strain extract and tested if the R strain could still be transformed.

What was the key conclusion of Avery, MacLeod, & McCarty’s experiment?

Transformation only failed when DNA was destroyed, proving that DNA is the transforming principle.

When polysaccharides, lipids, RNA, or proteins were destroyed in S strain extract, the R strain was still transformed and the mouse _____.

died

Scientists originally thought the transforming principle was _____

Protein

Avery, MacLeod & McCarty concluded:the transforming principle is

that DNA is the transforming principle.

Hershey & Chase (1952)

onducted the Waring blender experiment that demonstrated DNA is the genetic material.

Conclusion of Hershey & Chase = DNA is the _____, not protein.

genetic material

Replication

store information & transmit it to offspring through DNA copying process.

Gene expression = controls _____ and adult functioning.

development

Mutation = provides _____ for adaptation.

variation in traits

DNA building blocks = nucleotides (_____).

sugar, phosphate, base 

Chargaff’s rule = [A]=[T], [G]=[C], and (T+C) = (____ + ____).

A + G

Rosalind Franklin = produced X-ray diffraction image showing DNA is a ______

helix

Rosalind Franklin = produced ______ image showing DNA is a helix

X-ray diffraction

Watson determined bases exist in the more stable _____ form.

keto

Base pairs = A-T (____ bonds), G-C (____ bonds).

2,3

Linus Pauling = incorrectly proposed a _____ helix with bases on the outside.

triple

Watson & Crick (1953) = proposed the DNA model with bases on the (inside/outside).

inside

DNA = a _____.

double helix

DNA strands are