BIO 110 Chapter 4: Nucleic Acids and the Origin of Life PDF

Chapter 4 Nucleic Acids and the Origin of Life Nucleic Acids Are Informational Macromolecules Key Concept #1 4.1 Nucleic Acids Are Informational Macromolecules nucleotide: the monomer that makes up nucleic acids A nucleotide consists of a pentose sugar...

Chapter 4 Nucleic Acids and the Origin of Life Nucleic Acids Are Informational Macromolecules Key Concept #1 4.1 Nucleic Acids Are Informational Macromolecules nucleotide: the monomer that makes up nucleic acids A nucleotide consists of a pentose sugar, a phosphate group, and a nitrogen-containing base. Nucleic acids are specialized for storage, transmission, and use of genetic information. RNA = ribonucleic acid DNA = deoxyribonucleic acid Differences Between RNA and DNA RNA provides a readable genetic language enables genes to be expressed as proteins DNA provides long-term, genetic information storage can be easily copied and passed on to future generations Our genes are segments of DNA. 4.1 Nucleic Acids Are Informational Macromolecules RNA contains the sugar ribose. It is a “normal” sugar with one oxygen attached to each carbon atom. DNA contains the sugar deoxyribose. It is a modified sugar, lacking one oxygen. The difference of one oxygen makes the sugars easily distinguishable by enzymes in biological systems. 4.1 Nucleic Acids Are Informational Macromolecules The bases of nucleic acids are one of two chemical forms: pyrimidine: six-membered single- ring structure; cytosine (C), thymine (T) and uracil (U); “CUT the Py” purine: a fused double-ring structure; adenine (A) and guanine (G); “Pure As Gold” complementary base pairing: purines pair with pyrimidines by hydrogen bonds T (pyrimidine) :::: A (purine) C (pyrimidine) :::: G (purine) 4.1 Nucleic Acids Are Informational Macromolecules Nucleotides are linked by phosphodiester bonds (covalent bonds). Phosphate groups link the 3′ carbon in one sugar to the 5′ carbon in another sugar. Nucleic acids grow in the 5′-to-3′ direction. 4.1 Nucleic Acids Are Informational Macromolecules RNA: single-stranded, but base pairing can occur between different regions of the molecule which results in 3D structure Complementary base pairing can also take place between RNA and DNA. 4.1 Nucleic Acids Are Informational Macromolecules DNA: Two strands form a double helix. All DNA molecules have the same basic structure, but the sequence of base pairs differs. Genetic information is carried in the sequence of base pairs of a DNA molecule. 4.1 Nucleic Acids Are Informational Macromolecules replication: the process by which a DNA molecule is copied transcription: the synthesis of RNA using a DNA template; genes are the sequences of DNA that are transcribed into RNA translation: the synthesis of a polypeptide using the genetic information encoded in an mRNA molecule; there is a change of “language” from nucleotides to amino acids transcription + translation = gene expression 4.1 Nucleic Acids Are Informational Macromolecules DNA replication and transcription depend on the base pairing properties of nucleic acids. Genetic information is carried in the sequence of base pairs of a DNA molecule. DNA carries hereditary information from one generation to the next. genome: the complete set of DNA in an organism Closely related living species have more similar base sequences than do species that are more distantly related. DNA sequencing is now used extensively to trace evolutionary relationships. The Small Molecules of Life Originated on Primitive Earth Key Concept #2 4.2 The Small Molecules of Life Originated on Primitive Earth For much of history, people believed that living things could come from non-living sources or decaying matter by spontaneous generation: frogs developed from falling drops of rain (the Nile River) flies arose from decaying meat (open markets before refrigeration) Francesco Redi first disproved this in 1668. 4.2 The Small Molecules of Life Originated on Primitive Earth Experiments by Louis Pasteur showed that microorganisms can arise only from other microorganisms, not by spontaneous generation. But these experiments did not prove that spontaneous generation had never occurred. The Large Molecules of Life Originated from Small Molecules Key Concept #3 4.3 The Large Molecules of Life Originated from Small Molecules How did life first originate? There are two main ideas. chemical evolution Conditions on primitive Earth led to the formation of simple molecules which eventually led to life forms. life came from outside Earth Meteorites can contain purines, pyrimidines and amino acids. Chemical evolution is the more popular idea. How did polymers form? The appearance of catalysts would have been important. Most are proteins called enzymes. Proteins are synthesized from information in nucleic acids. Which appeared first, nucleic acids or protein catalysts? RNA may have been the first catalyst. RNA could have acted as a catalyst for its own replication and for the synthesis of proteins. DNA may have eventually evolved from RNA. Cells Originated from Their Molecular Building Blocks Key Concept #4 4.4 Cells Originated from Their Molecular Building Blocks Living cells are separated from their environment by a membrane. This allows cells to maintain a chemical composition that is different from the external environment. Experiments suggest how cells may have formed. In water, fatty acids will form a lipid bilayer around a liquid compartment. small molecules (sugars and nucleotides) could pass through this lipid bilayer short nucleic acid strands capable of self-replication may have been present 4.4 Cells Originated from Their Molecular Building Blocks Protocells may be a reasonable model for the evolution of cells: They are organized systems of interacting parts, in some cases catalytically. They have an interior that is distinct from the exterior environment. They can self-replicate.