Cell origins

Question 1

How did the first cells form? (4 steps)

Answer 1

1. Inorganic compounds e.g. CH4 or H2O formed simple organic compounds or biological monomers e.g. amino acids
2. Monomers come together to form polymers through polymerisation e.g. protein
3. A polymer is formed which can self-replicate (enables inheritance) - most likely RNA
4. Polymers are packaged into membranes which have internal chemistry different to surroundings (simple protocells)

Question 2

How was the theory of formation of cells proven?

Answer 2

Miller Urey experiment

• Conditions of early earth replicated - water was heated, then passed through electrodes to replicate electrical storms. Simple gases like H2, CH4 and NH4 also added to area where electrodes were, then the water passed through a condenser and was cycled back through experiment
• The gases reacted with water to form complex organic molecules - proving that inorganic molecules can form organic ones.

Question 3

LUCA meaning

Answer 3

Last Universal Common Ancestor

Question 4

Evidence that LUCA existed (2 points)

Answer 4

1. All living things now share some basic genes e.g. the instructions for DNA replication
2. All living things share genetic code (A,T,G,C,U) and all life carries out translation and transcription

Question 5

Features of hydrothermal vent (3 points)

Answer 5

• High temperatures
• Rich in minerals e.g. iron sulfide
• Abundant in H2, CH4 and other energy supplies

Question 6

Evidence for LUCA living in hydrothermal vents (3 points)

Answer 6

1. Fossils have been found in HTVs that date back to ~3.7 billion years ago
2. Genes of LUCA are involved in the use of hydrogen as an energy source
3. LUCA is thought to have possesed genes which are common in extremophiles existing in high temp environments (like HTVs)

Question 7

How do scientists predict dates of LUCAs existence? (4 points)

Answer 7

1. Biochemical signatures (chemicals produced from cellular processes) from stromatolites provide evidence of life 3.7 billion years ago
2. Fossils containing isotope ratios can help to predict when first cells formed
3. Comparing genomes of archaea and bacteria (most different organisms) help to predict how long ago they shared a common ancestor by looking at what genes they share & therefore what gene LUCA had
4. Comparing mutation rates of biomolecules (e.g. DNA, RNA) to deduce time since first cells. This assumes there is a direct correlation between number of mutations and time since species diverged.

Question 8

Fluorescent and immunoflourescent microscopy

Answer 8

Using flourescent die and attaching it to a specific antibody which target specific parts of cell and makes them glow

Question 9

Transmission electron microscopy vs scanning electron microscopy

Answer 9

TEM - Very detailed, black and white images which kill the cell in the process
SEM - higher resolution, 3D image which scans the surface of cell

Question 10

Freeze fracture electron microscopy

Answer 10

Freezing the cell and cracking it open with a blade - more detail than TEM and SEM

Question 11

Cryogenic electron microscopy

Answer 11

Flash freezing the cell to keep them in place and then viewing with a microscope - can see small proteins and molecules