DNA and Protein Production

DNA and Protein Production (Week 7)

Structure of DNA and Nucleotides

  • Structure of DNA:

    • DNA (Deoxyribonucleic Acid) consists of two strands forming a double helix.

  • Nucleotides in DNA:

    • Each nucleotide is composed of three components:

    • A phosphate group

    • A five-carbon sugar (deoxyribose)

    • A nitrogenous base

      • The four bases of DNA are:

      • Adenine (A)

      • Thymine (T)

      • Cytosine (C)

      • Guanine (G)

  • Order of Bonding:

    • The phosphate group of one nucleotide bonds to the sugar of the next nucleotide.

Bonds Holding Subunits Together

  • Type of Bonds:

    • Covalent Bonds:

    • Covalent bonds link the sugar of one nucleotide to the phosphate of another, forming the sugar-phosphate backbone.

    • Hydrogen Bonds:

    • Hydrogen bonds pair the nitrogenous bases: A pairs with T (2 hydrogen bonds) and C pairs with G (3 hydrogen bonds).

Drawing DNA

  • Abbreviations for Components:

    • Use one-letter abbreviations:

    • A = Adenine

    • T = Thymine

    • C = Cytosine

    • G = Guanine

    • S = Sugar (deoxyribose)

    • P = Phosphate

Steps of DNA Replication

  • DNA Replication Process:

    1. Unwinding:

    • DNA helicase unwinds the double helix and separates the two strands.

    1. Binding of RNA Primers:

    • RNA primase lays down RNA primers to initiate synthesis.

    1. Synthesis of New Strands:

    • DNA polymerase adds nucleotides to the growing new strand complementary to the template strand.

    1. Replacing RNA Primers:

    • RNA primers are replaced with DNA nucleotides.

    1. Ligation:

    • DNA ligase seals any gaps in the sugar-phosphate backbone.

Timing of DNA Replication

  • When Replication Occurs:

    • DNA replication takes place during the S-phase of the cell cycle, prior to mitosis.

Roles of Enzymes in DNA Replication

  • Helicase:

    • Unwinds the DNA strand, separating the two strands at the replication fork.

  • DNA Polymerase:

    • Synthesizes new DNA strands by adding nucleotides to the complementary template strand.

  • Energy Supply:

    • The energy required for this synthesis comes from the deoxynucleotide triphosphates (dNTPs) as they are incorporated into the growing DNA strand.

Point Mutations

  • Definition:

    • A point mutation is a change in a single nucleotide of a DNA sequence.

  • Recognizing Mutations:

    • Ability to recognize an incorrectly paired sequence (e.g., A instead of G).

  • Possible Outcomes of Mutations:

    • 1. Silent Mutations: No change in amino acid sequence.

    • 2. Missense Mutations: Change in one amino acid in the protein sequence.

    • 3. Nonsense Mutations: Change one codon to a stop codon, resulting in a truncated protein.

  • Positive Aspect of Mutations:

    • Mutations can lead to genetic diversity and evolution by providing new traits.

Structural Differences Between DNA and RNA

  • Structural Differences:

    • Sugar: DNA contains deoxyribose; RNA contains ribose.

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

    • Base Pairing:

    • In RNA, uracil (U) replaces thymine (T).

  • Structural Similarities:

    • Both contain nucleotides with phosphate groups and nitrogenous bases.

mRNA Complementation from DNA

  • Determining Complementary mRNA Sequence:

    • Transcription process:

    • A (adenine) in DNA pairs with U (uracil) in RNA.

    • C (cytosine) pairs with G (guanine), G pairs with C, T pairs with A.

Cell Parts and Protein Production

  • Key Cell Structures Involved in Protein Production:

    • Nucleus: Houses the DNA, where transcription occurs.

    • Ribosomes: Sites of protein synthesis using mRNA.

    • Endoplasmic Reticulum (ER): Rough ER synthesizes proteins, while Smooth ER is involved in lipid synthesis and detoxification.

    • Golgi Apparatus: Modifies, sorts, and packages proteins for secretion or delivery to other organelles.

Structure of Proteins

  • Structure of Proteins:

    • Proteins are made up of long chains of amino acids, which fold into specific three-dimensional shapes.

  • Monomer Units of Proteins:

    • The monomers of proteins are amino acids. There are 20 standard amino acids that combine in various sequences to form a protein.

Transcription and Translation

  • Transcription:

    • The process of synthesizing mRNA from the DNA template.

  • Where RNA Polymerase Binds:

    • RNA polymerase binds to a specific region on the DNA known as the promoter.

  • Function of RNA Polymerase:

    • Catalyzes the synthesis of RNA from the DNA template during transcription.

  • Steps of Transcription:

    1. Initiation

    2. Elongation

    3. Termination

  • Translation:

    • The process where the mRNA sequence is decoded to synthesize a specific polypeptide or protein.

  • Steps of Translation:

    1. Initiation

    2. Elongation

    3. Termination

Reading mRNA Codons

  • Reading mRNA to Make a Protein:

    • Utilize the genetic code (codon table) to translate mRNA sequences into amino acids. Codons are groups of three nucleotides that specify individual amino acids.

Types of RNA and Their Functions

  • Types of RNA:

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

    • tRNA (transfer RNA): Transfers specific amino acids to the growing polypeptide chain at the ribosome.

    • rRNA (ribosomal RNA): Combines with proteins to form ribosomes, the site of protein synthesis.

  • Location of Functions:

    • mRNA is synthesized in the nucleus and functions in the cytoplasm.

    • tRNA and rRNA function within the cytoplasm as part of the ribosomal machinery for translation.