DNA, Protein, Transcription & Translation

DNA and Protein – Overview

• This set of notes covers the basic concepts of DNA, protein structure, transcription, and translation.

• Key Chapters referred to:

  • Nucleic Acids: Chapter 2, pgs. 49-50

  • Proteins: Chapter 2, pgs. 45-48

  • Transcription: Chapter 9, pgs. 210-212

  • Translation: Chapter 9, pgs. 213-215

Nucleic Acids

• Two main types of nucleic acids are:

  • DNA: Deoxyribonucleic acid

  • RNA: Ribonucleic acid

• Function of DNA:

  • Constitutes the genome of cells

  • Serves as a template for RNA synthesis

• Function of RNA:

  • Involved in the synthesis of proteins using information derived from DNA

Structure of Nucleic Acids

• Single Nucleotide:

  • Building block of nucleic acids

  • Composed of three components:

  1. Nitrogenous Base

  2. Pentose Sugar (5-carbon sugar)

     • Deoxyribose: Found in DNA

     • Ribose: Found in RNA

  3. Phosphate Group

Nitrogenous Bases in Nucleotides

• DNA:

  1. Thymine (T)

  2. Adenine (A)

  3. Cytosine (C)

  4. Guanine (G)

• RNA:

  • Similar to DNA, except:

  • Uracil (U) replaces Thymine (T)

• Nucleotides link together to form nucleic acid polymers.

  • Example DNA Sequence: ATGCGCTGATGCTAGCTCG

  • Related RNA Sequence: ACGUCGCUUAGCGAUAGCU

Structure of DNA

• Double Helix:

  • DNA is typically double-stranded and composed of two helical chains.

  • The strands run anti-parallel to each other (3' to 5' and 5' to 3').

  • Complementary base pairing:

  • Adenine (A) bonds with Thymine (T)

  • Guanine (G) bonds with Cytosine (C)

  • Example of base pairing: ATGCGAGCTAGATCGTAG ↔ TACGCTCGATCTAGCATC

• Genes are sequences of DNA that code for molecules, typically proteins.

Differences Between RNA and DNA

• Stranding:

  • DNA: Double-stranded

  • RNA: Single-stranded

• Nitrogenous Bases:

  • DNA contains Thymine; RNA contains Uracil

• Molecule length:

  • RNA molecules are shorter than DNA molecules, as they represent specific genes.

Complementary Base Pairing

• Bases are held together by Hydrogen Bonds.

• Illustration of the bonding between bases:

  • A with T

  • G with C

Proteins

• Definition of Proteins:

  • Proteins are polymers composed of monomers called amino acids.

• Amino acids link together to form polypeptide chains, which eventually fold to form functional proteins.

General Structure of Amino Acids

• Each amino acid includes:

  • A central carbon

  • A carboxyl group (-COOH)

  • An amino group (-NH2)

  • A hydrogen atom

  • A variable R-group (side chain)

• There are 20 common amino acids.

Peptide Bonds

• Peptide bonds form when the amino group of one amino acid reacts with the carboxyl group of another, releasing a water molecule (dehydration synthesis).

  • Reaction results in a dipeptide or polypeptide chain.

List of Common Amino Acids

• With Names and Abbreviations:

  • Alanine (Ala, A)

  • Arginine (Arg, R)

  • Asparagine (Asn, N)

  • Aspartic Acid (Asp, D)

  • Cysteine (Cys, C)

  • Glutamic Acid (Glu, E)

  • Glutamine (Gln, Q)

  • Glycine (Gly, G)

  • Histidine (His, H)

  • Isoleucine (Ile, I)

  • Leucine (Leu, L)

  • Lysine (Lys, K)

  • Methionine (Met, M)

  • Phenylalanine (Phe, F)

  • Proline (Pro, P)

  • Serine (Ser, S)

  • Threonine (Thr, T)

  • Tryptophan (Trp, W)

  • Tyrosine (Tyr, Y)

  • Valine (Val, V)

Protein Structure

• Levels of Protein Structure:

  • Primary:

  • Sequence of amino acids in a polypeptide chain.

  • Example sequence: Methionine-Glycine-Alanine-Valine-Threonine-Tryptophan-Proline (Met-Gly-Ala-Val-Thr-Try-Pro)

  • Secondary:

  • Hydrogen bonding in the polypeptide backbone results in alpha helices and beta-pleated sheets.

  • Tertiary:

  • The three-dimensional shape of a protein resulting from side chain interactions.

  • Quaternary:

  • Assembly of multiple polypeptide chains into a functional protein.

  • Example: Hemoglobin, which carries oxygen in the blood.

Types of Proteins

• Structural: Maintain cell shape and support (e.g., Collagen, Keratin)

• Contractile: Involved in muscle movement (e.g., Actin, Myosin)

• Storage: Store nutrients (e.g., Ovalbumin, Casein)

• Protective: Defend against pathogens (e.g., Antibodies, Fibrinogen)

• Transport: Move molecules (e.g., Hemoglobin, Membrane Transport Proteins)

• Signal: Coordinate activity (e.g., hormones like Insulin)

• Communication: Signal transduction (e.g., Neurotransmitters)

• Enzymatic: Catalysts for biochemical reactions (e.g., DNA polymerase, RNA polymerase, DNA ligase)

Transcription and Translation Overview

• The flow of information from DNA to protein involves two key processes:

  1. Transcription: Synthesis of mRNA from DNA.

  2. Translation: Synthesis of proteins from mRNA.

Transcription Process

• Steps of Transcription:

  1. Initiation:

  • DNA unwinds in the region of mRNA synthesis called the transcription bubble.

  • The promoter is the DNA sequence where transcription machinery binds.

  1. Elongation:

  • RNA polymerase synthesizes the mRNA strand complementary to the DNA template strand.

  1. Termination:

  • Transcription stops when RNA polymerase reaches a termination sequence.

Translation Process

• Components of Translation Machinery:

  • rRNA: Part of ribosome structure.

  • mRNA: Carries genetic information from DNA.

  • tRNA: Brings specific amino acids matching the codon sequence.

• Steps of Translation:

  1. Initiation starts at the start codon (AUG) on mRNA.

  2. Each tRNA's anticodon pairs with the corresponding mRNA codon.

  3. Ribosome moves along mRNA, translating the codons into a polypeptide chain until reaching a stop codon, terminating translation.

Example Exercise

• Given a DNA strand: TACAGTTTAACATCTACT

  • Required Tasks:

  1. Find the complementary DNA strand.

  2. Transcribe the DNA to mRNA.

  3. Translate the mRNA to a peptide sequence using a codon table.