1.5 The Origin of Cells

Question 1

how are cells formed and why is this remarkable

Answer 1

cell can only be formed by division of preexisting cells

Therefore there is a continuity of life from its origins on Earth to the cells in our body today

cells have a nucleus with all the genes coding for the whole body

In 2010 there were reports of biologists making new cells however this was actually just extreme genetic modification as the cell was the base sequence of Mycoplasma mycoides transferred to a different bacteria cell Mycoplasma capricolum

it is currently impossible to create an entirely new cell.

Question 2

spontaneous generation - how did pasteur deal with it

Answer 2

Louis Pasteur - 1860

made a nutrient broth with Yeast and sugar and water and boiled it in seal flask and no spontaneous generation occured.

repeated it with a pad of cotton wool in the flask which had been in air and microorganisms appeared

then used swan necked flasks with different necks used some unboiled solution and some boiled solution

1. unboiled and sealed growth
2. boiled and sealed no growth

different shapes

1. if open neck and air can fall in growth
2. if curved and microorganisms get stucks - no growth

Question 3

why do choloplasts and mitochondria seem like they were prokaryotes engulfed by eukaryotes

Answer 3

1. they have their own genes - circular DNA molecules
2. 70S ribosomes - size like those of eukaryotes and means they can produce proteins
3. transcribe DNA and use RNA to synthesize some proteins
4. can only be prodcued by divison of preexisting mitochondria or chloroplasts

Question 4

what is endosymiosis?

Answer 4

It states that mitochondria were once free living prokaryotic organsims that developed the process of aerobic respiration.

Larger prokaryotes then englufed them and took them in by endocytosis

they then developed a mutuallistic relationship and, as long as mitochondria grew and divided as fast as the prokaryotic cell they continued on

mutualistic as

Mitochondria gets food

Prokaryotic cell gets gets energy supply

natural selection favours these cells so they increase in number and take over

same with cholorplast - one taken in and photosynthesises is allowed to grow and divide.

Question 5

How did the very first cell arise?

Answer 5

must have arisen from non-living material

main stages ( one hyptotheses)

• production of carbon compounds e.g. sugar and amino acids

Miller and Urey passed steam through a mixture of methane, hydrogen and ammonia. - representative of earth’s atmosphere - then electrical discharged used to simulate lightinign –> amino acids produced

• assembly of carbon compounds into polymers

`around deep sea vents which carry reduced organic chemicals e.g. iron sulphide which are readily accessible supplies of energy which was used to assembly the carbon compounds into polymers

• formation of membranes

if phospholipids or otehr amphipathic carbons are among these first carbons they naturally assemble into a bilayer. These readily form vesicles resembling the plasma mambrane of a small cell - allows a different internal chemistry from that of the surroundings to develop

• development of a mechanism for inheritance

to replicate DNA and pass on genes to offspring you need enzymes, but for enzymes you need genes – kmaybe RNA was a first genetic material as it is both self-replicating and can act as a catalyst to itself

basically

INORGANIC COMPOUNDS –> in special conditons fused to form –> ORGANIC COMPOUNDS —> cells made of organic compounds

in increasing complexity

carbohydrates - cell membrane, sugar phosphate backbone

lipids - cell membrane, cholesterol

proteins - enzymes, hormones, antibodies

DNA - to replicate and reproduce