Origins of cells - evolution of cells Flashcards
What are cells considered to be?
Cells are considered to be the smallest units of life.
What features do all cells have in common?
- Enclosed by a plasma membrane
- Store genetic information in DNA
- Capable of metabolic processes
How can life be defined?
- Occurrence of metabolic reactions
- Need for nutrition
- Production of metabolic waste
- Ability to reproduce
- Ability to receive and respond to stimuli
- Ability to grow
True or False: Viruses are considered living organisms.
False
What do viruses lack that prevents them from performing most characteristics of life?
Viruses lack a cell structure and organelles.
What are the steps required for the first cells to originate from non-living components?
- Synthesis of simple organic compounds
- Assembly of simple organic compounds into polymers
- Development of self-replicating polymers
- Formation of membranes around polymers
What is the protocell-first theory?
This theory proposes that a cell-like compartment capable of basic metabolic functions arose spontaneously.
Describe the gene-first theory.
This theory suggests that a nucleic acid capable of self-replication developed spontaneously.
What does the metabolism-first theory propose?
Life originated as a system of chemical reactions capable of sustaining itself.
Why is testing theories on the origin of cells challenging?
It is impossible to replicate early Earth conditions exactly and no early cells fossilized.
What role do membranes play in cells?
They separate genetic material and biochemical processes from the outside environment.
What is theorized to have formed the membranes of the first cells?
The membranes were likely composed of fatty acids.
How do lipid molecules behave in water?
They form a monolayer, with polar parts in water and non-polar parts sticking out.
What are microspheres?
Small vesicles that could have formed the membranes of early cells.
What is the RNA world hypothesis?
RNA may have performed both replication and catalysis functions in early cells.
List properties of RNA that support its role in early life.
- Can assemble spontaneously from nucleotides
- Can replicate itself
- Can control the rate of chemical reactions
What evidence supports the idea that RNA predates DNA?
- Ribose can be formed from methanal
- Deoxyribose in DNA is produced from ribose
- Ribozymes can join amino acids to form proteins
What four things are essential for the evolution of early cells?
- catalysis
- self-replication of molecules
- self-assembly
- compartmentalisation of different cell parts
