Named Scientists Flashcards
1
Q
Davson-Danielli – Plasma membrane structure
A
- Electron microscope
- Cell membrane mad of both phospholipids and proteins
- Lipid layer was sandwiched between two protein layers
- Dark segments under electron microscope were identified (wrongly) as representing the two protein layers
- Assumes all membranes were a uniform thickness
- Assumes all membranes would have symmetrical internal and external faces
- Did not accept permeability of certain substances
2
Q
Singer-Nicolson - Plasma membrane structure
A
- Proteins were embedded within the lipid bilayer rather than existing as separate layers
- Fluid-mosaic model
3
Q
Pastuer – Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth
A
- Cells come from pre-existing cells
- Boiled a nutrient broth
- The sterile nutrient broth was placed in three flasks and left to incubate
- A sample of each flask was transferred to plate contained solid medium and incubated
- Only the flask that was exposed to air had bacterial growth
4
Q
Crick and Watson – DNA structure
A
- DNA strands are antiparallel and forma double helix
- DNA strands pair via complementary base pairing
- Outer edges of the bases remain exposed
- Built a model to represent this
5
Q
Meselson and Stahl – Semi-conservative nature of DNA replication
A
- Experimentally tested that validity of 3 models (conservative, semi-conservative, and dispersive) using radioactive isotopes of nitrogen
- Nitrogen is a key component of DNA and can exist as N15 or N14
- DNA molecules were prepared using the heavier N15 and then induced to replicate in the presence of the lighter N14
- The results after two divisions supported the semi-conservative model of DNA replication
- After one division, DNA molecules were found to contain a mix of N15 and N14 disproving the conservative model
- After two divisions, some molecules of DNA were found to consist solely of 14N, disproving the dispersive model
6
Q
Cairn – Technique for measuring the length of DNA molecules by autoradiography
A
- Used autoradiography to visualise the chromosomes whilst uncoiled, allowing for more accurate indications of length
7
Q
Mendel – Genetic crosses with pea plants
A
- Researched inherited factors on the flowers of pea plants
- Artificially crossed the pea plants and examined the inheritance of variation in seven different traits of the plants
- Crossed one trait at a time
- Had a known history of the parent plants
- Counted offspring
- Experiment was repeated
- Concluded that genes work in pairs
- Each of the pair is called an allele
- Assumes each trait was controlled by a pair of inherited factors
- Assumes each individual has 2 factors
- Assumes each factor is a discrete particle (did not blend to change the identity of the factor)
8
Q
William Harvey – Movement of blood
A
- Heart acts as a double pump
- Blood is continuously circulated to/from lungs and to/from body
- Studied year of animal dissections and human cadaver dissections
- Blood flows in one direction
- Valves prevent back flow
9
Q
Galen – Ancient Greek philosopher – movement of blood
A
- Blood is created in the liver from ingested food and flow to the right side of the heart
- Some flows to he lungs where it gives of ‘sooty vapours’
- Some flows through invisible pores into the left side of the heart whee it gains ‘vital spirits’ when mixed with pneuma brought in by trachea
- Theory based on idea
- Blood is constantly being used up in the body
- Did not consider the closed circulation pattern
10
Q
Florey and Chain – Tests on penicillin
A
- Tested penicillin on infected mice
- 8 mice were injected with bacteria
- 4 mice were also injected with penicillin
- The untreated mice died from bacterial infection
- Mice treated with penicillin all survived demonstrating antibiotic potential
11
Q
Franklin and Wilkins – Structure of DNA by x-ray diffraction (HL)
A
- X-ray diffraction to investigate the structure of DNA
- DNA was targeted by an X-ray beam, which was diffracted when it contacted an atom
- The scattering pattern of the X-Ryan was recorded on a film and used to elucidate details of molecular structure
- DNA helix is tightly packaged and regular in structure
12
Q
Hershey and Chase – DNA is genetic material (HL)
A
- Viruses were grown in one of two isotopic mediums in order to radioactively labels specific viral component
- Viruses grown in radioactive Sulfur had radio labelled proteins (Sulfur present in proteins but not DNA)
- Viruses grown in radioactive phosphorus had radio labelled DNA (phosphorus is present in DNA but not proteins
- Viruses were allowed to infect E.coli and then the virus and bacteria were separated via centrifugation
- The bacterial pellet was found to be radioactive when infected by the DNA viruses but not the protein viruses
- Demonstrates that DNA was the genetic material because DNA was transferred to the bacteria
13
Q
Calvin – Pathway of carbon fixation (HL)
A
- Used chlorella algae which was placed in a thin glass vessel
- Algae was given light, carbon dioxide, and hydrogen carbonate
- At the start, carbon compounds were replaced with compounds containing radioactive carbon C14
- Samples of algae were taken at different time intervals
- The carbon compounds were separated by chromatography and the compounds donating C14 identified by autoradiography
- Demonstrated a series of steps in the cycle
14
Q
Thomas Hunt Morgan - Developed the notion of linked genes to account for the anomalies (HL)
A
- Discovered non-Mendelian ratios in fruit flies
- Linked genes were not independently assorted
- Discrete pairs f factors are located on chromosomes
- Certain characteristics are sex-linked
- Other characteristics are also sometimes associated
15
Q
Jenner - Tested his vaccine for smallpox on a child (HL)
A
- Jenner deliberately infected a young boy with cowpox from blisters of a milkmaid with the disease
- Jenner attempted to infect the boy with smallpox, but found that he as immune
