AMK Chapter 4 EPCC PowerPoint PDF

CHAPTER 4 Nucleic Acids and an RNA World  LESSON OUTLINE 4.1 – What is a nucleic acid? Analyze the characteristics of nucleotides and the bonds that link them together in nucleic acids 4.2 – DNA structure and function Analyze the different...

CHAPTER 4 Nucleic Acids and an RNA World  LESSON OUTLINE 4.1 – What is a nucleic acid? Analyze the characteristics of nucleotides and the bonds that link them together in nucleic acids 4.2 – DNA structure and function Analyze the different levels of DNA structure and how they are related to DNA function 4.3 – RNA structure and function Analyze the different levels of RNA structure and how they are related to RNA function 4.4 – Could life have evolved from an RNA? Evaluate the hypothesis that life began as an RNA molecule  Chemical evolution led to production of molecule that could self replicate Deoxyribonucelic acid (D N A): Stores genetic information and is replicated using proteins R N A world hypothesis: I N T R O D U C T I ON Proposes time in evolution where R N A both stored genetic information and catalyzed its own replication Once self-replicating molecules evolved, process of evolution began  Nucleic Acids Biological Function: Responsible for the storage, expression, and transmission of genetic information Two classes Deoxyribonucleic Acid (DNA) Stores genetic information encoded in the sequence of nucleotide monomers Ribonucleic Acid (RNA) Decodes DNA into instructions for linking together a specific sequence of amino acids to form a polypeptide chain  4.1 WHAT IS A NUCLEIC ACID? Nucleic acid—polymer of nucleotide monomers any of a group of long, linear macromolecules, either DNA or various types of RNA, that carry genetic information directing all cellular functions: composed of linked nucleotides. Three components of nucleotide: 1. Phosphate group 2. Five-carbon sugar 3. Nitrogenous (nitrogen- containing) base  WHAT IS A NUCLEIC ACID? Ribonucleotides are monomers of R N A: Have ribose as their sugar Has an -OH group bonded to the 2’ carbon Deoxyribonucleotides are the monomers of D N A: Sugar is deoxyribose (deoxy = “lacking oxygen”) Has H instead at 2′ carbon Both sugars have –OH group bonded to 3’ carbon  WHAT IS A NUCLEIC ACID? Two groups of nitrogenous bases: 1. Purines — contain nine atoms in their two rings: Adenine (A) Guanine (G) 2. Pyrimidines — contain six atoms in their one ring: Cytosine (C) Uracil (U) – found only in ribonucleotides (RNA) Thymine (T) – found only in deoxyribonucleotides (DNA) FIGURE 4.1 THE GENERAL STRUCTURE OF A NUCLEOTIDE  HOW DO NUCLEOTIDES P O LY M E R I Z E T O F O R M N U C L E I C AC I D S ? Nucleic acids polymerize via condensation reactions Phosphodiester linkage (bond) occurs between: Phosphate group on 5′ carbon of one nucleotide and –OH group on the 3’ carbon of another Polymer produced is RNA Phosphodiester linkages join ribonucleotides together: Polymer produces id RNA  DNA AND RNA STRANDS ARE DIRECTIONAL Phosphodiester linkages form a sugar– phosphate backbone Backbone is directional (5′ → 3′ direction): One end has unlinked 5′ phosphate group Other end has unlinked 3′ hydroxyl group Primary structure of D N A written by listing sequence of bases by single-letter abbreviations: Example: 5’ – ATTAGC – 3’  POLYMERIZATION REQUIRES AN ENERGY SOURCE Nucleic acid polymerization: Can take place in cells by use of enzymes Potential energy is raised by adding two additional phosphate groups Creates nucleoside triphosphates ”activated nucleotides” Example of activated ribonucleotide: Adenosine triphosphate (A T P) Energy is released when activated nucleotides polymerize: Makes reaction spontaneous  WHAT IS THE NATURE OF DNA’S SECONDARY STRUCTURE? Early data provided clues to DNA James Watson and Francis Crick secondary structure: Rosalind Franklin determined: DNA polymerized through formation Two strands are held together by hydrogen bonds between of phosphate linkages pyrimidines and purines Molecule had sugar–phosphate Complementary base pairing backbone (Watson–Crick pairing) occurs Number of purines equaled number of between A and T, C and G pyrimidines: DNA strands are antiparallel Equal number of T’sand A’s; equal Antiparallel strands predicted to number of C’s and G’s twist together to form double helix: X-ray crystallography used to measure distances between atoms in The sugar–phosphate backbone faces exterior DNA: Nitrogenous base pairs face Predicted helical structure FIGURE 4.6 THE SECONDARY STRUCTURE OF DNA IS A DOUBLE HELIX  DNA forms more compact three- dimensional structures in cells: Length of DNA in each cell is approximately 6 feet long Two forms of DNA Tertiary structure DNA is wound too tightly or THE TERTIARY loosely; twists to form STRUCTURE OF DNA supercoils DNA wraps around DNA-binding proteins called histones Less dependent on primary structure compared to proteins It is important to transport DNA during cell division  DNA FUNCTIONS AS AN INFORMATION- CONTAINING MOLECULE Watson and Crick’s Franklin's model revealed DNA as the biological reservoir of information: Stores information required for organism’s growth and reproduction Information consists of sequences of nucleotides in nucleic acid: Four nitrogenous bases function like letters in an alphabet Sequence of bases has meaning, like order of letters in a word How is this information replicated?  HOW IS DNA REPLICATED? DNA replication has three steps:  Two strands are separated by breaking hydrogen bonds  Free deoxyribonucleotides form hydrogen bonds with complementary bases on original strand of DNA (template strand)  Phosphodiester linkages form to create new strand, called complementary strand  Complementary base pairing allows each strand to be copied exactly producing two identical daughter molecules  Double helix is highly structured: Held together by phosphodiester linkages, hydrogen bonds, and hydrophobic interactions Functional groups participate in chemical reactions Makes molecule stable and resistant to degradation THE DNA DOUBLE HELIX Stability of DNA key to IS A STABLE STRUCTURE effectiveness of reliable information-storage molecule The reason why detectives/forensic scientists can solve crimes Yet no support for hypothesis that first life form consisted of DNA alone  Complementary strands DNA is composed of two complementary antiparallel strands What does that look like: 3’-TATGTATATTACGTG-5’ 5’-ATACATATAATGCAC-3’ Check out this YouTube video linkfor additional info: https://www.youtube.com/watch?v=alM_BhVfNtg The sequence of one strand of DNA is shown below. Which of the following is the sequence of its complementary strand? 3 ATTTGGCC 5 A. 5′ ATTTGGCC 3′ B. 5′ TAAACCGG 3′ C. 3′ ATTTGGCC 5′ D. 3′ TAAACCGG 5′ Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved The sequence of one strand of DNA is shown below. Which of the following is the sequence of its complementary strand? 3 ATTTGGCC 5 A. 5′ ATTTGGCC 3′ B. 5′ TAAACCGG 3′ C. 3′ ATTTGGCC 5′ D. 3′ TAAACCGG 5′ Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved  4.3 RNA STRUCTURE AND FUNCTION Primary structure of R N A: Four types of nitrogenous bases extending from sugar–phosphate backbone Primary structure of R N A differs from D N A: 1. R N A contains ribose instead of deoxyribose 2. R N A contains uracil instead of thymine 3. 2’ –OH group on ribose is more reactive than –H 4. RNA is much less stable than DNA  RNA SECONDARY STRUCTURE R N A ’ s secondary structure results from complementary base pairing: A with U; G with C Bases of R N A typically form hydrogen bonds with complementary bases on the same strand R N A strand folds over, forming hairpin structure: Bases on one part of R N A strand fold over and align with bases on other part of the same strand Two sugar–phosphate strands are anti- parallel  RNA TERTIARY STRUCTURE R N A molecules can also have tertiary structure: Forms when secondary structures fold into more complex shapes R N A much more diverse in size, shape, and reactivity than D N A DNA AND RNA STRUCTURE  RNA highly versatile: RNA can function as a Folds into complex catalytic molecule three- Ribozymes: dimensional RNAs have catalyze shapes reactions Structure flexibility Three-dimensional allows them to structure vital to perform many tasks catalytic activity RNA As intermediate Have active sites, like PROPERTIES between DNA and proteins protein, mRNA Ability to catalyze transmits phosphodiester information bonds giving rise to Regulate production possibility that RNA of mRNA from DNA could replicate itself Capable of catalyzing reactions What determines the primary structure of RNA? A. the sugar–phosphate backbone B. complementary base pairing and the formation of hairpin loops C. the sequence of deoxyribonucleotides D. the sequence of ribonucleotides Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved What determines the primary structure of RNA? A. the sugar–phosphate backbone B. complementary base pairing and the formation of hairpin loops C. the sequence of deoxyribonucleotides D. the sequence of ribonucleotides Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved  4.4 IN SEARCH OF THE FIRST LIFE-FORM Theory of chemical evolution: Life began as naked self-replicator Molecule in solution not enclosed in membrane To copy itself, first living molecule had to: Provide template that could be copied Polymerize monomers into copy of that template RNA capable of both processes: Most researchers propose first life-form was made of RNA  HOW BIOLOGISTS STUDY THE RNA WORLD One study attempted to generate RNA molecule that could catalyze RNA “replicase:” Protocol designed to mimic process of natural selection Succeeded in isolating ribozyme capable of adding 14 nucleotides to existing RNA strand Another study looked into possibility of ribozyme that could make RNA nucleotides that could add uracil base: Mimicking natural selection, team purified ribozyme that could perform such a task, a million times more efficient  AN RNA WORLD MAY HAVE SPARKED THE EVOLUTION OF LIFE Most modern ribozymes aid protein production: If removed, proteins could not be made Therefore, R N A probably preceded proteins Evolution of protein enzymes would have marked end of R N A world Three characteristics of life solidly in place: 1. Information processing 2. Replication of hereditary information 3. Evolution by random changes in nucleic acids