Evolution test

Why are viruses considered non-living?

• They are not made out of cells

• They cannot keep a stable state

• They cannot reproduce indepndently

• They cannot perform metabolic functions independently

• They do not grow

What are structural features common to viruses?

• Smal, must be 20-30nm (smaller than host cell so it can infest it)

• Fixed size

• Capsid (to hold genetic materials, composed of proteins )

• Genetic material-nucleic acid like dna or rna is used as genetic code

• No cytoplasm

• Little enzymes (only for replication of genetic material)

• However, features are varied in structure, suggesting various evolutionary origins

Types of genetic mateiral in viruses

Positive sense Rna viruses use the genome directly as mrna

Negative sense RNa viruses have to transcribe this info (probably have more enzymes.?)

RETROVIRUSES: Make double stranded DNA to replace the dna material within cells.

What are te two shapes of capsids ?

Helical or icosahedral (few have complex architecture)

Non-enveloped viruses

Bacteriophage lambda

• INfects mainly e.cola bacteria

• Does not have a membrane surrounding it

• makes it more resistant to extreme ph, heat, dryness and disinfectancts

• Main form of cell exit is LYSIS

• Bursting out of the cell

• Causes significant cell and tissue death for the organism

Enveloped viruses

• Go through a budding process from host membrane (er membrane, golgi membrane, or the cell membranes)

• Phospholipids (and proteins alr present in the virus) envelop the virus

• Make it more resistant to enzymes within the host cell (animal cells haev more)

• This happens when they BREAK FREE (do NOT bud off)

• Tend to be more sensitive to heat, dryness, pH or disinfectants

The viral genome

• Differs in size, type of gene, number

• All have the same mission→ to hijack host cells to..

• To create more nucleic acid (dna or rna) virus genetic material

• To assemble virus proteins

• To create more virus molecules

Lytic cycle

• Attachment-phage attaches itself to receptor proteins

• Random collisions occur randomly

• Injection of DNA material

• Phages have tails that are sheathed in contractile proteins

• Coiled structures inject for genetic materials

• Replication of phage Dna by host cell machinery

• Positive sense rna is used directly as mrna

• Negative sense rna is transcribed into mrna

• DNA is adapted in a rolling circle replication

• Enzymes nick one strand

• The 3’ strand will be synthesized by enzymes in the cell machinery and linear strand wll be built off of the DNA strand

• Linear strand will join at the ends later

• Host cell machinery will translate genetic material into viral proteins.

• Viral proteins will form into viral components. The capsid protins will form empty heads, while tails will develop independently. they will then come together to form a progeny

• Enzymes will be released and will weaken cell membrane.

• Viral material will burst out of the cell

Lysogenic Cycle

• Temperate form of a virus

• Prophage DNA infects host cell genome

• The cells replicate into daughter cells and passively maintain the prophage dna

• Under stressful conditions, cell excises the prophage dna and virus enters the lytic cycle

Three virus hypotheses

• Virus first

• Viruses were before cells as a self replicating unit, which co-evolved with cells

• Also, they developed the ability to infect later

• Lack of fossil records for virus (can only measure protein structure)

• Progressive hypothesis

• Taking and modfying cell components

• This is seen in similarity between transposons and viruses, cell components can be modified and added materials

• Regressive hypothesis

• reducing cell components

• Autonomous replication of selfish cell components

• Convergent evolution from LUCA, can be seenin similar protein structures

• Operate on same genetic code as cells and bacteria

• very few shared features indicate convergent evolution

Why do viruses evolve very quickly?

• Generation rates

• (Very short amount of time between generations, one hour can pass, a lot of offspring in generation)

• Lots of offspring creates competition, this creates natural selection

• High mutation rates

• Virus not being sable gies it high mutation rates in which protein structures change a lot

• But some mutations are beneficial and allow it to infect to new host cells or to avoid cell immuno functions

• Natural Selection

• Lots of offpsinrg→ more competition

• Host cell immune measures and defenses against viral cells makes it so that there are more selection pressures

• selection pressures drive evolution

Retro virus

• Uses RNA as genetic material

• RNA is more unstable and more prone to mutation because rna does not have any proofreading mechanisms, as compared to DNA

HIV

retrovirus that is prone to high mutations due to its protein structure

its high mutation rate allowed various novel strains of the virus to appear, making it more deadly

What were the conditions on early earth that allowed carbon compounds to form?

• High in water vapour

• High in lightning

• Volcanoes spewed gases like methane, hydrogen sulfide, and carbon

• These gases allowed for UV to penetrate atmosphere but it was trapped, which heated the earth

• Oxygen appeared as photosyntesizing organisms arose

• Gradual cooling occured

• then carbon compounds formed

Functions of life

• Nutrition

• Metabolism

• Gr oth

• Excretion

• Homeostasis

• Reproduction

• Response

How does Paramecium indicate that the cell is the smallest unit of self-sustaining life?

• Nutrition- vacuole stores organisms consumed by paramecium and releases it into the cytoplasm

• Metabolism- Most metabolic pathways happen in the cytoplasm

• Growth - After assimilating and absorbing biomass, the paramecium will undergo cell division

• Excretion- Cell membrane regulates the movements of substances in and out of the cell, including waste products of metabolism

• Homeostasis- Contractile vacuole will store or expel water to maintain the water levels stable in the cell

• Reproduction- Nucleus will divide to support cell division by mitosis, often occuring asexually

• Response- Cilia moves paramecium in response to environmental conditions, ex to chase food

What are the key problems to the spotaneous origin of cells?

• If there was a time before cells existed, that means that they synthesized from non living conditions

• Otherwise, they wee transported here someow from another part of our universe

• Non living synthesis of organic molecules like sugars and amino acids

• Formation of polymers

• Formation of membrane to package organic molecules

• Self replication of polymers (enabling inheritcance)

Evidence for the origin of carbon compounds on Earth

• Miller Urey experiment mimicked conditions of early earth

• Used a glass vessel (mimics closed atmosphere)

• High temperature

• High radiation

• Reducing atmosphere (with little oxygen)

• Mimiced electrical storms

• Boiled water to turn into vapour, mixed with hydrogen, ammonia and methane

• This was let cool, and after a week compounds like nucleic acids, amino acids and COMPLEX OILY HYDROCARBONS WERE FORMED

Coalesence of fatty acids to form membranes

• MEMBRANES provide boundary between the inside cell and the surrounding environment

• This allows compartmentalization to happen and allows the cell to carry out more functions and subsequently become more complex

• Phospholipids (fatty acids) forms a cell size arrangement that creates a vesicle (called liposome)

• Formed sometime during early earth, hydrophilic heads faced outwards, hydrophobic tails faced inwards

• Spherical bilayer

The formation of polymers that can self replicate & first genetic material

RNA! (Ribnucleic acid)

• Is abl to store information

• Less stable than dna, but can caalyze formation of copies of itself (ribozymes)

• Can also compose peptide bonds

• Can self assemble into strands from nucleotides

• Dna cannot do this and is not the presumed genetic material because enzymes are required and it cannot self replicate

Overview of the major stages of the origin of life

• Early earth

• abiotic chemical compounds

• Small organic molecules

• polymers of organic molecules

• protocell

• cell

Evidence for LUCA

• Last common ancestor

• Shares the same genetic code as all cells

• Shares the same molecular transport processes

• Contains building blocks for DNA and Rna as genetic material (similar to all cells)

• Over 3000 genes or sections of DNA is common to all cells

• Hypothesized- other organisms but LUCA’s descendants were just better and were able to reproduce on earth

Radioactive Isotopes

Form of absolute dating

• Radioisotopes are alternative forms of an element that have the same number of protons, diff number of neutrons

• Isotopes are unstable and decay at a constant rate to form a more stable daughter isotope

• Half-life, the isotope decays at a constant rate, and turns into a more stable form

• People can guess, if this isotope is present, and it takes this amount of time to decay, this is how old the organism is

• Compares the ratios, it reveals the time

Relative dating

Looking at the fossil index in dimension of time, layer of rock can be used to deduce the age of the fossil.

The fossils within the layer are called index fossils.

However, its not fully accurate because it can provide inaccurate ages

Hypothesis for organisms that can survive without light

• Deep sea fissure vents release heat energy and also organic chemical compounds

• Organic polymers arise

• In 1977, a red and white tubeworm was discovered that absorbs minerals from the water

• They get transferred to symbiotic bacteria, the bacteria make food from minerals

• The food nourishes the worms

What are the origins of eukaryotic cells

• Ier ebrae of geeic aterial fored folds ad created a ebrae arog geetic etaerial

• developed folds to optiizete sface area to vole retio

• Te cleoid regio was fored

• itocoria ad chloroplasts

• Both are ssceptible to atibacteri, proteopacteri tat was aerobic was accpeted ito anaerobic prokaryote.