Origin of cells, cell structure and virus (HL)

Explain how it could be possible for carbon compounds to form spontaneously on the early earth

1. Early early conditions are very different than they are today

2. Very little UV absorbing Ozone

3. Early earth atmosphere had high concentrations of methane and carbon dioxide

Outline the smallest units of life

1. Cells

2. Not virus because they are non living

List two necessary requirements for the evolution of first cells

1. Catalyst - to speed up reaction

2. Compartmentalization

3. Some form of genetic material (eg. DNA or RNA)

Most important challenges in explaining the spontaneous origin of cells

1. The process was very complicated

2. This happened 3.5 billions years ago, evidence might be damaged

Strength and weakness of Miller and Urey experiment

Strength: It formed several organic molecules

Weakness: Composition of atmosphere not the same

Outline the current understanding about the method by which fatty acids could have compartmentalize the first cells from the environment

1. Bubbles of lipid have formed

2. Early cytoplasm formed

Reasoning which led RNA to be the first genetic material at the same time as enzymes

1. Protein/enzymes are needed to make DNA, RNA could provide a solution

2. There is no logical reasoning to which came first

Outline the evidence that supports the idea that the LUCA evolved in the vicinity of hydrothermal vents

1. Hydrothermal vents are still active under the sea

2. Fossil evidence has been found in the vicinity of hydrothermal vents

Summarize two methods used to estimate the time of the first living cells

1. Analysis of radioactive isomer, estimate age of rock

2. Molecular clock

Why are fatty acids or phospholipids important in the formation of cells and their component

They allow compartmentalization of cells and organelles

Early earth conditions of concentration of oxygen, ozone and carbon dioxide

Oxygen: Almost zero

Ozone: Almost zero, very little UV absorbing it

Carbon dioxide: Very high

Why virus are non living

1. They cannot reproduce independently, rely on host cell

2. They do not respire

Why RNA is more likely to be first genetic material than DNA

1. RNA can be replicated

2. RNA can code for protein synthesis

3. RNA has catalytic property

The Miller-Urey experiment produced organic molecules in an atmosphere that, in 1952, was thought to have been like the atmosphere on earth prior to the evolution of life. In which way was the experiment's model atmosphere different from today's scientific understanding of the atmosphere at the origin of life on earth?

The atmospheric conditions used in Miller's investigation contained high concentrations of methane and ammonia, but the early Earth atmosphere is now thought to have much lower concentrations of these gases.

Explain why the conditions on Earth today make the spontaneous formation of organic

carbon compounds less likely compared to the conditions on Earth at the time of the origin of life

1. Present day has more oxygen in atmosphere

2. Less UV light passing through atmosphere

3. Lower concentration of methane

4. UV light can provide energy to form organic molecules

List the essential features that the first cells must have possessed to be able to live and

evolve into the life forms that followed

1. Ability to self replicate

2. Have genetic material

3. Contain catalytic properties

4. Compartmentalization

Where eukaryotes come from

1. Come from common ancestor

2. Through sexual reproduction

3. Have nucleus

3. Eukaryotes evolved from prokaryotes

Highlights 1st endosymbiosis

1. Eukaryote evolved from prokaryote

2. It is then engulfed by cells aerobically (endocytosis)

3. Then develops to mitochondria which is taken into our cells

Highlight 2nd endosymbiosis

1. Mitochondria is already engulfed

2. Photosynthetic bacterium is engulfed

3. Becomes eukaryotic cell with mitochondria and chloroplast

Evidence of endosymbiotic theory

1. Mitochondria and chloroplast have similar size of prokaryotes

2. They have double membranes

3. Naked DNA

4. Have 70s ribosomes

5. Replicate through binary fission

Highlight cell differentiation

Highlights turning on and off genes that are necessary for a specific function controlled by changes in the environment

Example of specialized cells

1. Bone cells

2. Blood cells

3. Muscle cells

4. Skin cells

5. Nerve cells

Features share by all virus

1. Contain either DNA or RNA as genetic material

2. Capsid made of protein

3. Can only be seen under an electron microscope

What is a capsid

A protein shell that surrounds and protect the genetic material

Which strand does HIV, influenza and bacteriophage lambda have

HIV and influenza: Single strand RNA

Bacteriophage lambda: Double stranded DNA

Is HIV and influenza enveloped?

1. Yes it is enveloped which is a membrane that surrounds the capsid made of lipids and proteins

2. Acquired from host cell and helps virus attach to host cell

What does it mean if bacteriophage lambda is not enveloped?

1. It is more stable

2. Resistant to environmental factors

How do virus rely on host cell?

1. Energy: it does not have its own source of energy so it gets it from the host cell

2. Nutrients: Do not have ability to obtain their own nutrient, rely on host cell

What are the two types of genome reproduction?

Lytic and lysogenic cycle

Explain the lytic cycle

1. Phage attachment to host cell

2. Phage DNA entry into host cell

3. Phage DNA replication

4. Phage protein synthesis

5. Assembly of new phage viruses

6. Host cell will burst

7. Spread

Explain the lysogenic cycle

1. Phage attachment to host cell

2. Phage DNA entry into host cell

3. Phage DNA is integrated into host genome

4. DNA replication

5. Cell division

Difference between lytic and lysogenic cycle

1. In lysogenic, no viral particles are produced

2. In lysogenic, host cell is not destroyed

3. Lysogenic takes a longer period of time

Similarity and difference of lytic and lysogenic cycle

Similarity:

1. Both are processes of phage reproduction

2. Both cycles start with phage proteins binding to host cell receptors

3. Both DNA/RNA will be injected in

Difference:

In lytic cycle the host cell will be killed in contrast of lysogenic

Highlight how viruses may have originated

1. From ancient DNA or RNA that became encapsulated

2. They may have evolved from viroids

3. May have evolved from ancient cells that lost their ability to live independently

What is convergent evolution?

Unrelated organisms independently evolve similar traits as a result of adapting to similar environments

How convergent evolution occured?

1. Virus infect different cell types to evolve and replicate

2. After it evolve, it will spread to new host cell

3. After they spread to new host cell, they will evolve to have similar shapes and sizes

4. Because they have evolved many different cell types, it can adapt to changes very easily

Why virus evolve faster than organisms?

1. Due to high mutation rates

2. They copy genetic material using error prone

3. Virus have short generation time and reproduction rates are very high

This means higher mutation is harder to treat and vaccinate

Evidence supporting that diversity of virus exist as a result of convergent evolution

They have similar features,

1. Have capsid

2. Have spikes

3. Share same genetic code

4. Rely on host cell for metabolic processes

Similarity and difference of a virus

Similarity:

1. Have capsid

2. Have spikes

3. Spherical shape

4. RNA as genetic material

Difference: They have difference strand of RNA and DNA

How do viruses vary?

1. Size

2. Shape

3. Genetic material type

4. Enveloping

What type of genetic material do viruses use

1. All use nucleic acid

2. Some use DNA or RNA

Advantages of comartmentalisation

1. Enzymes are concentrated, more collisions will occur

2. Protects remaining structures from degradation

3. Maintain optimum pH