How did life arise? Cells to Organisms

Question 1

What are the characteristics/traits of a virus in terms of the characteristics of an organism?

Answer 1

Against:
- cannot carry out physiological functions
- not made up of independent cells and are dependent on the host cell

For:
- contain genetic information
- evolve over time

Question 2

What did viruses evolve from?

Answer 2

Even though viruses are not cellular organisms, it is highly likely they evolved from cellular life forms because of their dependence on them

Many biologists also use this to categorise them as living organisms

Question 3

How did life arise?

Answer 3

• arose from non-life by chemical evolution
• the earth was formed 4.5-4.6 billion years ago, and life emerged 600 million years ago
• random physical and chemical interactions of atoms produced large variety of molecules, further interactions led to the evolution of life
• the development of an internal and external environment due to the enclosure of complex biological molecules through lipid membranes caused the first cells with the ability to self replicate to arise
• photosynthesis occured, producing oxygen and allowing the o-zone to be created. This then could protect organisms to be protected against radiation which the allowed for life outside of water, and generally more complex organisms to occur

Question 4

Describe the evolution of cell structure and its importance

Answer 4

enclosure of complex proteins and other biological molecules by membranes that contained them in a compact internal environment that seperated them from the surrounding (external) environment

fatty acid molecules, due to their insolubility, played a large role in the development of cellular membranes

this lead to the development of an internal and external environment, concentrated reactants and products, and led to the first cells with the ability to replicate themselves; the evolution of the first cellular organisms

Question 5

The characteristics of cells

Answer 5

1. All cells come from, pre-existing cells
2. The molecular structure and properties of cells define their functions
3. Cells are bounded by a membrane and maintain internal environments that differ from their external environments
4. Cells communicate with each other
5. Cells can form organised units capable of more complex function

Question 6

What is the fundamental cell theory

Answer 6

1. Cells are the fundamental units of life
2. All living organisms are comprised of cells
3. All cells come from pre-existing cells
4. Modern cells evolved from a common ancestor

Question 7

What are the two key theories of how life arose on Earth?

Answer 7

1. Life formed spontaneously on earth (a reducing environment facilitated the organic molecule formation such as DNA bases
2. Extraterrestrial origin. e.g. comets/meteorites carrying the essential molecules for life (amino acids, DNA etc.) to our planet and then life stemmed from this

Question 8

What was the cambrian explosion?

Answer 8

A rapid diversification of life took place approximately 541 million years ago, which is commonly referred to as the cambrian explosion
Most of the major animal groups living today appeared during the cambrian period

Question 9

What are stromatolites and why are they important?

Answer 9

Stromatolites
a calcareous mound built up of layers of lime-secreting cyanobacteria and trapped sediment, found in Precambrian rocks as the earliest known fossils.

They thrive in hyper-saline water.

As the layers form they trap water and other debris and lock it away, including cyanobacteria, and therefore allowed for the fossilisation of bacteria, allowing us to see what early life looked like

And this also provides a strong timeframe as to when life first arose .

Question 10

When did water arise?

Answer 10

Water is very common both most of it is in the form of ice
Water has been found on earth for at least 383.8 billion years
Pillow basalt- a type of rock- proved the existence of water as it trapped and stored it, suggesting there was water at that date

Question 11

Properties of water

Answer 11

• High melting point and boiling point in comparison to smaller molecules
• High heat of vaporisation
• High Cohesion (hydrogen bonding between h20 molecules)
• High Adhesion (attraction of water to other molecules)

Question 12

Features common to all lifeforms

Answer 12

• Composed of a common set of chemical compounds: mainly Carbohydrates, fatty acids, nucleic acids and amino acids
• Made up of cells
• Use molecules obtained from the environment to synthesise new Biological molecules
• Extract energy from the environment and use it to do work
• Regulate their internal environments
• Contain genetic information, genomes, that enables them to develop, Maintain themselves, function and reproduce
• Use a universal molecular code to build proteins from their genetic information
• Exist in a population that evolves over time

Question 13

Benefits and costs of viruses

Answer 13

Pros:
- Contain nucleic acids (as small s 2-3 kbp
- Viruses can replicate
- Evolve and adapt to the environment
Cons:
- Not capable of independent replication
- Do not contain required metabolic processes to be considered alive
- Are not comprised of cells or organelles
- Cannot extract energy

Question 14

What evidence does DNA provide to explain evolution?

Answer 14

All living organisms use the same genetic code,
Which leads scientists to believe that living organisms all evolved from the same source, rather than from separate sources.
Suggests a common origin about 4 billion years ago
All organisms arose from earlier more primitive forms the past 4 billion years through the processes of evolution
Because all organisms are related they share the same genetic code, chemical composition, and cellular structure
Biochemical unit of life

Question 15

When did life arise on earth? 9 key events with times

Answer 15

1. formulation of earth (start of Hadean period)
2. first oceans (end of Hadean period)
3. Origins of life (start of Archean period)
4. Origins of Photosynthesis (end of Archean/start of Proterozoic period)
5. first colonial cyanobacteria (start of proterozoic period)
6. first eukaryotes (middle of proterozoic period)
7. first photosynthetic eukaryotes (middle of proterozoic period)
8. first multicellular eukaryotes (middle/end of proterozoic period)
9. first fossils of multicellular animals (early phanerozoic period)

Question 16

How did photosynthesis effect life?

Answer 16

Early in earth’s history, the atmosphere and oceans had zero oxygen, high co2, ammonia, methane and intense radiation
Photosynthetic cyanobacteria changed all of that as it increased the level of oxygen. The increase of oxygen allowed them to interact with each other and create free radicals, which then recombined with oxygen molecules and could create o-zone
600 million years ago a thin o-zone layer which could protect against radiation and then allowed for more complex life to evolve in the oceans and then on land

Question 17

what are the two domains of life that are prokaryotic?

Answer 17

Bacteria
Archaea

Question 18

How to archaea differ from bacteria?

Answer 18

• look same
• over half of the Archaean genes are new to science, therefore differeing genes
• archaea are nearly as different from bacteria as they are from eukaryotes genetically
• genetic transcription and translation are more similar to eukarya and use more than one enzyme, differing again from bacteria
• archaea lack a peptidoglycan wall and use an ether bond instead in their membranes
• have not been found to produce resting spores/ endo spores

Question 19

Common features between all prokaryotes

Answer 19

all have:
- A cell membrane
- DNA located in a region called the nucleoid
- Cytoplasm: the rest of the cell contents (majority of the cell)
- Ribosomes: sites of protein synthesis

most have:
- a call wall outside the plasma membrane made of peptidoglycan

Question 20

some bacteria have:

Answer 20

• A capsule made of polysaccharides
• A call wall and a capsule which provides protection from adverse environmental conditions
• They can also have a flagellum for locomotion
• Pili (fimbriae) attachment structures, involved in the exchange of DNA
• Often a cell wall made of a peptidoglycan
• Sometimes an outer membrane

Question 21

Diference between prokaryotic and eukaryotic ribosomes S units

Answer 21

pro=70S
euk: 80S
S= sveberg units

Question 22

How to classify bacteria

Answer 22

You can use Gram staining to categorise bacteria

It stains the cell wall and whether or not it stains shows what type of bacteria it is

this is because bacteria with similar cell walls also have similar interternal environments

Question 23

Gram Positive

Answer 23

• simple cell wall
• single layer, thick cell wall (20-80nm)
• Peptidoglycan layer is thicker or multilayered
• no outer membrane
• low lipid levels
• susceptible to antibiotics
• less toxic
• peptidoglycan layer, plasma membrane, the thick peptidoglycan layer traps the purple crystals (cell wall structure)
• have low antibiotic resistance because it is less complex
• more peptidoglycan overall

STAINSSS

Question 24

Gram Negative

Answer 24

• Structurally complex cell wall
• Double-layered, thin cell wall (8-10nm)
• Thin, single peptidoglycan layer
• Outer membrane usually present
• 20-30% lipids
• Very resistant to antibiotics
• Usually more toxic as it is harder to kill
• Outer membrane, peptidoglycan layer, plasma membrane (structure of cell wall)
• more resistant to antibiotics because of its complexity of cell wall
• less peptidoglycan overall

DOESN’T STAIN

Question 25

examples of unusual prokaryotes

Answer 25

they are diverse and ubiquitous - thermophilic (like hot) - acidophilic (like acid) bacteria like this live in hot sulphur springs with high Ph and temperature or deep sea hydrothermal vents some can also survive without oxygen

Question 26

Difference and similarities between prokaryotes and Eukaryotes

Answer 26

prokatyotes - no membrane bound organelles - cell wall made of peptidoglycan (excl. archaea) - have a plasma membrane - have cytoplasm - have DNA as free in the Nucleoid in the cytoplasm - simple and can mutate quickly - flagella made of flagellin, has a hook and sleeve eukaryotes - membrane bound organelles - cell wall made of cellulose etc. in plants - has a plasma membrane - has cytoplasm - has DNA as chromosomes in the nucleus - complex and can't mutate quickly - flagellum has a plasma membrane that are more complex, has proteins involved and has more efficient movement

Question 27

What is a nucleus?

Answer 27

- Surrounded by a double membrane or nuclear envelope - Presence of nuclear (annular) pores (50nm in diameter). The pores allow rna to pass in and out - Nucleolus= subregion of nucleus containing (transcribing) ribosomal genes (ribosomal biogenesis) - DNA is in the nucleus - DNA is in long strands covered with histones = chromosomes - Different organisms have different numbers of chromosomes - RNA transcribed from DNA leaves nucleus via pores and is translated in the cytoplasm - The nucleus is a chromosome containing organelle of a eukaryotic cell - Chromosomes = genetic material, one long DNA molecule - Each chromosome is made up of material called chromatin a complex proteins and DNA - Each eukaryotic and prokaryotic species has a characteristic number of chromosomes

Question 28

What is a Mitochondria?

Answer 28

- Cells may contain several of these organelles or have a single, large mitochondrion - They are surrounded by two membranes, an outer membrane and a highly convoluted inner membrane, whose inward projections are called cristae - Mitochondria carry out the aerobic respiration of all eukaryotic cells - Outer membrane controls the interior space of the organelle- keeps it separate and in the conditions we want for the cell - Inner membrane is highly folded for a high surface area to volume ratio to enable efficient reactions - Aerobic respiration occurs in the mitochondria

Question 29

what are chloroplasts

Answer 29

- Cells may contain one or many chloroplasts per cell - They are surrounded by two membranes, an outer membrane plus an inner membrane that forms complex internal network of lamellae or thylakoids - The photosynthetic pigments are located within the thylakoids - Chloroplasts are responsible for photosynthesis, or the conversion of light energy to chemical energy - The pigments are lipids.

Question 30

How did the nucleus evolve?

Answer 30

- The nucleus may have formed from invaginations of the plasma membrane around the nucleoid of an ancient prokaryote (also how ER was formed) - Invagination- dips and folds developing

Question 31

What is primary endosymbiosis?

Answer 31

- Mitochondria arose from primary endosymbiosis of a purple bacteria- this single event gave rise to the mitochondria in all eukaryotes - It has its own DNA, which implies it had its own origin (bacterial) - Chloroplasts arose from primary endosymbiosis of a photosynthetic cyanobacteria- this single event gave rise to the chloroplasts in all algae and land plants process 1. It was consumed and a vacuole built around it (phagocytosis) 2. Because of a mutation or something else (bacteria or vacuole), bacteria doesn’t get eaten. 3. Vacuole comes apart and then the bacteria lives inside the cell. 4. Becomes an endosymbiont. 5. Then transfers its DNA into the genome of the other bacteria it then becomes an organelle not an endosymbiont - Note: when primary endosymbiosis the organelle has 2 membranes evidence: - Cyanophora with cyanelles- contains a dividing plastid (early version of chloroplast), with a peptidoglycan wall between its membranes- strong evidence that it was originally a bacteria that was engulphed

Question 32

Secondary endosymbiosis

Answer 32

Secondary (or eukaryotic) endosymbiosis - A chloroplast derived from an endosymbiotic, eukaryotic cell rather than a prokaryote - Several protist groups such as euglenoids, dinoflagellates and haptophytes obtained chloroplasts this way - "protistan pirates" - Also involves phagocytosis - eukaryote eats another eukaryote - One cell eats another who already has a chloroplast organelle - Responsible for 60% of the oxygen we use (in water doing photosynthesis)

Question 33

Why do some organelles have more than 2/3 membranes?

Answer 33

Each membrane indicates it has been eaten by another cell Therefore if it has 4, it means that the original bacteria with the chloroplast/mitochondria was consumed by a bacteria and integrated, then it was consumed again and integrated

Question 34

Evidence for the endosymbiotic origin of mitochondria and chloroplasts

Answer 34

- These organelles are very similar morphologically to bacteria - They are surrounded by an outer membrane similar to a cell membrane while their inner membrane invaginates to form lamellae or cristae - Mitochonfria and chloroplasts are semi-autonomous, retaining their own genome - They also retain their own machinery for synthesising proteins including ribosomes; their metabolism is like existing prokaryotic organisms (cyanobacteria for chloroplasts and a purple bacteria for mitochondrion) - The chloroplasts in some species still have the bacterial peptidoglycan wall between the inner and outer membranes (for example cyanophora)