BSCI 170 - Molecular Inheritance

Start of Unit 3

When was the structure of DNA discovered? By who?

• 1953

• Watson, Crick, Franklin

What is genetic material?

material used to store information necessary for a cell, an organelle, or a virus to carry out all physiological activities and to replicate itself

When cells maintain a genetic program directing faithful reproduction, what does one cell become?

two

What are three things that must happen to genetic information during faithful reproduction?

• stored and protected

• read out in a way that cells can understand

• transferred unchanged to the next generation

What does it mean that the transfer of proteins is irreversible?

DNA becomes RNA and vice versa. However, RNA is only used to create a protein which is not reversible

Was the identification of DNA as the genetic material a single or multistep process?

multistep

• Who identified the genetic material?

• What did they work with?

• What did they discover about inheritance?

• How do traits behave?

• Traits can be either…

• Gregor Mendel

• Garden peas

• Traits can be inherited independently

• Traits behave as discrete units

• Dominant or recessive

By the early 1900s, a few things were known.

• When do chromosomes segregate?

• When is the number of chromosomes halved?

• Where are genes located?

• during cell division

• germ cell formation

• on chromosomes

• Who developed drosophila as a model organism for genetics?

• What did they prove?

• T.H. Morgan

• Proved that genes are located on chromosomes and mapped them

What do we know by about 1940?

• What do genes code for?

• Where are genes located?

• What are chromosomes composed of?

• recognizable traits

• on chromosomes

• protein and DNA and RNA

Protein, DNA, and RNA: Which of these is the gene?

• Most scientists focused on proteins

  • What are some key characteristics of proteins?

  • What was DNA believed to be?

  • What was RNA believed to be?

  • What was more known about?

• structurally and functionally diverse and complex

• too simple and too small

• too unstable

• proteins

Who is Frederic Griffith?

• What did he discover?

  • How many strains are there?

• a Britsh edical microbiologist

• Streptococcus pneumoniae

  • two

What are the two strains (varieties) of streptococcus pneumoniae?

• R strain (benign) which lacks a protective coat, so it is recognized by host’s immune system

• S strain (virulent) which has a polysaccharide coat that prevents detection by host’s immune system

Transformation

• What is this in terms of R and S cells?

• What occurs during transformation?

• What did this initiate?

• R cells were converted into S cells

• something “passed” from nonliving cells to living cells

  • changed nonpathogenic cells into being pathogenic

    • Heritable and permanent

    • Changed the genetic material

• This initiated a 14-year search for the transforming principle

for your reference

N/A

What are bacteriophages?

• bacteria eaters

• viruses that infect bacteria

• take over cell metabolism to make more phage particles

• composed of DNA and protein only

T/F: Nucleic acids contain phosphorus but not sulfur

true

T/F: Protein contains both sulfur and phosphorus

false; only contains sulfur

Which two amino acids have sulfur in the side chain?

cysteine and methionine

What are isotopes?

element with same number of protons but different numbers of neutrons

What are the most common isotopes that are stable?

• Sulfur-32: 16 protons/16 neutrons

• Phosphorus-31: 15 protons/16 neutrons

Some isotopes are unstable and lose energy to regain stability, how is this energy loss detected?

as radioactivity

What are some useful radioactive isotopes? What do they do?

• Sulfur-35: 16 protons/19 neutrons

  • labels proteins; not nucleic acids

• Phosphorus-32: 15 protons/17 neutrons

  • labels nucleic acids; not proteins

What were some conclusions of the experiment with the bacteriophages?

• genes are transferred during phage infection

• DNA, not protein, is transferred during infection

• genes are composed of DNA

• conclusions accepted with little controversy

Before the bacteriophage experiment, what was thought of DNA?

• DNA was believed to be too simple to store information

What are Chargaff’s Rules?

• In any given organism:

  • [A] = [T] and [G] = [C]

  • Ratio of A:T = 1 and Ratio of G:C = 1

• The concentrations of the nucleotides are different in different organisms

• The concentrations of the nucleotides are the same in different tissues in the same organism

What are the different forms of DNA? What do these result in?

A form of DNA (reduced hydration), B form of DNA (highly hydrated)

• these result in very different x-ray diffraction patterns

Which form of DNA makes better crystals than the other?

A form makes better crystals than the B form

Rosalind Franklin was able to capture of the B form of DNA, what was determined from this?

• DNA is a helix

• width and density of diffraction lines in the crystal suggested two strands not three

How are bases in DNA arranged? What principle was used to determine this?

• Since two purines together would be too wide and two pyrimidines together would be too narrow, a purine and pyrimidine together would be consistent with x-ray data

• This is the Goldilocks Principle

Watson-Crick Base Pairing

• When polymer strands are antiparallel, how do stabilitizing hydrogren bonds form?

when purines pair with pyrimidines