ODU BIOL292 ch11

In light of recent achievements in the field of genomics, would it be reasonable to expect that the use of comparative genomics might shed light on the extinct genomes of early life?

Comparative genomics and studies of bacteria with very small genomes shed light on a common ancestor, and researchers can estimate the minimal characteristics that a cell would need to operate as a living organism.

Which of the following statements about LUCA is NOT correct?

It refers to a single, ancestral organism.

The origin of cell structures might be hypothesized to have involved a hypercycle, based on mutualism at the molecular level. Which of the following is correct regarding the hypercycle model?

Natural selection will favor a hypercycle that is enclosed in a membrane.

minimal gene set

The hypothetical minimal number of genes thought necessary to allow for cellular-based life. (page 426)

phylogenetic event horizon

The point in the history of life beyond which phylogenetic analysis is uninformative because there are no surviving descendants from ancestors before this point. See also last universal common ancestor (LUCA). (page 406)

last universal common ancestor (LUCA)

The population of organisms at the base of the tree of life. All living things today are descended from this one lineage. (page 406)

RNA world

A hypothetical early stage in the history of life in which RNA was the fundamental unit upon which life was based, fulfilling both an informational role (much as DNA does today) and a catalytic role (much as protein-based enzymes do today). (page 404)

hypercycle model

A model for the evolution of early life involving multiple types of replicators, each of which facilitates the replication of another in cyclical fashion. (page 413)

protocell

A simple cell-like entity that predated cellular life-forms in the history of life. (page 406)

vesicle

A small, fluid-filled compartment surrounded by a lipid membrane. (page 409)

mutualism

An ecological interaction in which different individuals, often of separate species, act so as to increase each other's fitness. (page 413)

prebiotic soup

An ensemble of simple organic molecules suspended in liquid water prior to the emergence of life on Earth. (page 407)

Why did the role of horizontal gene transfer ultimately become diminished over evolutionary time?

As cells became more complicated, they also became more integrated, less modular and less likely to take up new genes by horizontal gene transfer.

The human parasite Mycoplasma genitalium, with one of the smallest genomes of any organism that can be grown in a laboratory, as well as Chlamydia trachomatis, an obligate intracellular parasite, are examples of the types of organisms that functional genomics researchers have focused on. What is the main purpose of the study of such genomes?

By studying such genomes, researchers try to discover the basic and essential cellular functions of early life

Which of the following statements regarding the benefit of making the switch from an RNA- to a DNA-based genetic system during the evolution of life is correct?

DNA is a more stable molecule because deoxyribose is less reactive than is ribose.

What do we know about horizontal gene transfer (HGT) in the evolution of early life?

HGT was probably a powerful force during early cell evolution, leading to complex cellular organisms.

In 1977, Sidney Fox tried a different approach to testing the prebiotic synthesis of biological molecules. He mixed a number of different amino acids together at a high temperature (120°C) in an environment lacking water. When he subsequently placed the mixture into water to investigate what the amino acids would form, what happened next?

He found some peptide-like structures, but the bonds between the amino acids were weak and unstable.

The first genetic material on Earth was most likely __________.

RNA

ribozymes

RNA molecules with enzymatic function. (page 416)

abiogenesis

The emergence of life from a nonliving precursor. (page 407)

prebiotic soup hypothesis

The idea that the earliest life emerged in a "souplike" liquid environment, drawing upon energy from cosmic rays, volcanic eruptions, and Earth's own internal heat. (page 407)

molecular mutualism

When different molecules act such that they increase each other's rate of replication. See also mutualism. (page 413)

Stanley Miller and Harold Urey developed and conducted experimental tests for a "prebiotic soup" model of the origin of life, which had been proposed a few decades earlier by Aleksandr Oparin and J.B.S. Haldane. What did Miller and Urey show could be synthesized abiotically?

amino acids