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Nucleic Acids and Protein Synthesis: Study Guide

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Nucleic Acids and Protein Synthesis

Nucleic Acid Basics

Nucleic acids are essential biomolecules that store and transmit genetic information in living organisms. They are polymers made up of repeating units called nucleotides, and play a central role in heredity and protein synthesis.

  • Nucleic Acid: A polymer composed of nucleotide monomers. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

  • Formation: Nucleic acids are formed via dehydration synthesis reactions, where water is removed as nucleotides are joined together.

  • Nucleoside: Consists of two components: a nitrogenous base and a pentose sugar.

  • Nucleotide: Consists of three components: a nitrogenous base, a pentose sugar, and a phosphate group.

  • Phosphodiester Bonds: Nucleotides are linked together by phosphodiester bonds between the phosphate group of one nucleotide and the sugar of the next.

  • Primary Structure: The sequence of nucleotides in a nucleic acid chain. This sequence encodes genetic information.

Example: The DNA sequence AGCT encodes genetic information that can be transcribed and translated into proteins.

DNA Structure and Replication

DNA is the molecule that stores genetic information in cells. Its structure and replication are fundamental to inheritance.

  • Double Helix: DNA consists of two strands that coil around each other to form a double helix. The strands run in opposite directions (antiparallel).

  • Complementary Base Pairing: Bases on one strand pair with specific bases on the other: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).

  • Hydrogen Bonds: Complementary base pairs are held together by hydrogen bonds.

  • Replication: The process by which DNA makes a copy of itself before cell division.

  • Semiconservative Replication: Each new DNA molecule consists of one original (parent) strand and one newly synthesized strand.

  • Determining Complementary Sequence: Given a DNA template strand, the complementary strand can be determined by base pairing rules (A↔T, G↔C).

Example: If the template strand is 5'-ATCG-3', the complementary strand is 3'-TAGC-5'.

DNA vs. RNA

DNA and RNA are both nucleic acids but differ in structure and function.

  • Sugar: DNA contains deoxyribose; RNA contains ribose.

  • Bases: DNA uses thymine (T); RNA uses uracil (U) instead of thymine.

  • Strands: DNA is typically double-stranded; RNA is usually single-stranded.

  • Functions:

    • mRNA (messenger RNA): Carries genetic information from DNA to ribosomes for protein synthesis.

    • rRNA (ribosomal RNA): Forms the core of ribosomes and catalyzes protein synthesis.

    • tRNA (transfer RNA): Brings amino acids to the ribosome during translation.

Example: mRNA is synthesized from a DNA template and then used to direct protein synthesis.

Transcription

Transcription is the first step in protein synthesis, where the information in DNA is copied into mRNA.

  • Definition: The process of synthesizing an RNA molecule from a DNA template.

  • Process: RNA polymerase reads the DNA template and synthesizes a complementary mRNA strand.

  • Base Pairing: In RNA, adenine (A) pairs with uracil (U) instead of thymine.

  • Codon: A sequence of three mRNA bases that codes for a specific amino acid.

  • Determining mRNA Sequence: Given a DNA template, replace A with U, T with A, C with G, and G with C (for the coding strand, use the same sequence but replace T with U).

Example: DNA template: 3'-TACGGA-5' → mRNA: 5'-AUGCCU-3'

Translation

Translation is the process by which the sequence of bases in mRNA is used to assemble amino acids into a protein.

  • Definition: The process of synthesizing a protein from an mRNA template.

  • Codon Table: Each mRNA codon specifies a particular amino acid.

  • Determining Amino Acid Sequence: Use the codon table to translate mRNA codons into amino acids.

  • tRNA Anticodon: The sequence of three bases on tRNA that is complementary to an mRNA codon.

Example: mRNA codon: AUG → tRNA anticodon: UAC → Amino acid: Methionine

Mutations

Mutations are changes in the nucleotide sequence of DNA, which can affect protein synthesis and function.

  • Definition: A mutation is a permanent change in the DNA sequence.

  • Types of Mutations:

    • Substitution: One base is replaced by another.

    • Insertion: One or more bases are added to the sequence.

    • Deletion: One or more bases are removed from the sequence.

    • Frameshift: Insertions or deletions that change the reading frame of the gene.

Example: A substitution mutation changing a codon from GAA (glutamic acid) to GUA (valine) can alter the resulting protein.

Additional info:

  • Phosphodiester bond formation can be represented as:

  • Hydrogen bonds between base pairs: (2 H-bonds), (3 H-bonds)

  • General equation for dehydration synthesis:

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