Comprehensive Coverage: Dive deep into the world of biomolecules and cells. These notes provide in-depth insights into essential topics, including the structure and function of biomolecules (proteins, nucleic acids, lipids, and carbohydrates) and the inner workings of cells.
Cellular Processes U...
Evolution
The diversity of life can be explained by the process of evolution.
Cells
Cells are the fundamental structural and functional unit of life.
Information
Living systems have multiple mechanisms to store, retrieve, and transmit information.
Regulation
Biological processes are chemical in nature; biological organisms maintain homeostasis.
Interconnectedness
Living systems are interconnected and interacting.
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, DEFINING LIFE
How do we define life?
• Life is defined as any system capable of eating, metabolising, excreting, breathing,
moving growing, reproducing, and responding to external stimuli (the environment).
• All life:
- Grows and changes
- Is comprised of cells
- Uses and produces chemical molecules
- Extracts energy for use
- Contains genetic information (DNA)
- Exists in populations and can evolve.
Are Prions and Viroids Alive?
• Prions are misfolded proteins that can transmit their
misfolded shape onto normal variants of the same protein.
That’s how they are able to replicate and grow.
• Cause neurological diseases with a progressive course –
usually fatal.
• General biological consensus is that prions and viroids are
not living because they do not contain:
- DNA (genetic information)
- Cells ß-pleated sheets Green – normal protein
instead of alpha- Red - prion
- An energy metabolic system. helices
Are Viruses Alive?
Alive arguments
• Contain nucleic acids (as small as 2-3 kbp).
• Viruses can replicate.
• Evolve and adapt to the environment (thus respond to external stimuli).
Not alive arguments
• Viruses are not capable of independent replication (require a host to grow).
• Do not contain required metabolic processes to be considered “alive”.
The Origins of Life on Earth
Two schools of thought:
1. Life formed spontaneously on early Earth (through an environment facilitated organic molecule formation, such as
DNA bases)
2. Extra-terrestrial origin – life originated from microorganisms or chemical precursors of life present in outer space
(panspermia).
First: Life from Earth
• Series of experiments conducted by Miller and Urey seeked to mimic conditions thought to have existed on Earth 4
billion years ago.
• The experiments revealed that such conditions could result in the production of
organic products:
- Bases in DNA and RNA (A, C, G, T, U)
- All 20 amino acids found in proteins
- A range of 3- and 6- carbon sugars
- Fatty acids
- Vitamin B6, NAD and organic acids.
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, Second: Life from elsewhere
• Life or its building blocks may have originated elsewhere (presumably under similar conditions to
those identified in the Miller-Urey experiments) and arrived on Earth via meteorites.
• Evidence to suggest this theory includes samples from a meteorite landing in Australia in 1969, and
was analysed to contain amino acids, DNA bases and sugars.
• Hence, these organic compounds are not specific to Earth but the conditions.
Formation of Protocells from Fatty Acids
How did the first cell membranes come into existence?
• Fatty acid molecules form spherical structures called protocells.
• Small molecules such as nutrients and nucleotides pass through the “membrane”
and enter the protocell, where they copy an already present RNA template.
• Nucleic acids inside the protocells could replicate using the nucleotides from
outside (without enzymes) to create polynucleotides, which may have been the
first step toward cell reproduction.
• However, the protocells could not fully reproduce, nor could they carry out all the
metabolic reactions in modern cells.
• Protocell does exhibit these fundamental characteristics of living cells:
- Acts as an organized system of parts, with substances interacting and reacting (with or
without enzymes).
- Includes an interior that is distinct from the exterior environment.
- Is capable of limited replication.
Cell Theory
• States that:
- Cells are the fundamental unit of life.
- All living organisms are comprised of cells.
- All cells come from pre-existing cells.
- Modern cells evolved from a common ancestor.
What do the similarities among living organisms indicate?
• All life on Earth has a common ancestor.
• Evidence points to a common origin of life on Earth about 4 billion years ago.
• All organisms have arisen from earlier, more primitive (ancient) forms through processes of evolution.
• Because all organisms are related, they share the same genetic code, chemical composition, and cellular structure.
Evolution by Natural Selection
• Natural selection involves the selection of the phenotype most suited to overcome the environmental selection
pressure.
• Organisms more suited to an environment have higher genetic fitness, due to an advantageous phenotype, which
arises due to the presence of certain alleles.
• Over time, the fitter organisms have a selective advantage and are more likely to survive and pass on their alleles to
the next generation.
• This increases the allele frequency of the alleles that code for the advantageous phenotype.
• Thus, there are strong theories to support the following timeline:
1. Non-living Earth
2. Emergence of biomolecules for life
3. Formation of protocells
4. Formation of cellular structures that can propagate (reproduce)
5. Evolution into the complex forms of life today
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