Biology Topic 1 Summary - Chromosomes, DNA, and Protein Synthesis

Biology Notes

Chromosomes and DNA

  • Nucleic Acid: Stores and transmits genetic information. Composed of nucleotides made up of:

    • Phosphate
    • Sugar
    • Nitrogenous base

  • Types of Nucleic Acids:

    • DNA: Blueprint for building and maintaining organisms with instructions for protein synthesis.
    • Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)
    • RNA: Helps convert DNA genetic information into proteins.
    • Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)

  • Chromosomes (X-shaped):

    • Composed of chromatin, which is tightly coiled DNA around histone proteins.
    • Formed during cell division and become visible when chromatin replicates.
    • Eukaryotes: Linear chromosomes found in the nucleus; bound to proteins.
    • Prokaryotes: Singular circular chromosomes, unbound to proteins; found in cytosol.
    • Mitochondria and chloroplasts: Each contains circular DNA, unbound to proteins.

DNA Replication

  • Process: Allows transmission of genetic material from parent to daughter cells; results in genetically identical cells.
  • Structure: Double-stranded, antiparallel strands held by weak hydrogen bonds.
  • Semi-conservative replication: Each new daughter DNA consists of one old and one new strand.
  • Steps in DNA replication:
    1. DNA helicase breaks hydrogen bonds, separating the two strands.
    2. Primase synthesizes RNA primers to initiate replication (reads template strand 3’ to 5’, builds complementary 5’ to 3’).
    3. DNA polymerase links complementary nucleotides.
    4. DNA ligase seals the DNA.

Genes and Protein Synthesis

  • Gene Expression: Process where DNA directs RNA and protein synthesis (includes transcription and translation).
  • Exons and Introns:
    • Exons: Coding sequences in genes.
    • Introns: Non-coding segments of genes.
    • RNA Splicing: Introns are removed, exons joined to form processed mRNA.
Transcription Steps:
  1. DNA unzips (hydrogen bonds between bases break).
  2. Template strand is read; free RNA nucleotides (A, U, G, C) join to form mRNA in a 5’ to 3’ direction.
  3. mRNA exits the nucleus via nuclear pores.
  4. DNA zips back up.
  • mRNA Structure: Composed of RNA bases in triplets called codons, each coding for a specific amino acid.
Translation Steps:
  1. mRNA attaches to ribosome (with rRNA).
  2. tRNA, carrying an amino acid and anti-codon, binds to mRNA codon.
  3. tRNA anti-codon matches with mRNA codon.
  4. Each amino acid forms peptide bonds with the next.
  5. The last amino acid (STOP codon) signals completion of the polypeptide chain.
  6. Polypeptide folds into its functional protein shape.

Protein Structure and Function

  • Amino Acid Structure and Function:
    • Sequence determines shape, shape determines function.
  • Protein Shapes:
    • Primary: Linear sequence of amino acids.
    • Secondary: Folding patterns (alpha-helices and beta-pleated sheets).
    • Tertiary: 3D structure based on side chain interactions.
    • Quaternary: Multiple polypeptide chains combined.
Denaturation and Renaturation:
  • Denaturation: Loss of 3D structure due to temperature, pH, or salt concentration; results in loss of function.
  • Renaturation: If conditions return to normal, proteins may regain shape and function.
Types of Proteins:
  • Enzymatic Proteins: Speed up chemical reactions; unique shape allows substrate binding.
  • Receptor Proteins: Bind hormones/neurotransmitters; communicate messages to cells.
  • Hormonal Proteins: Signaling molecules like insulin; only affect cells with complementary receptors.
  • Defensive Proteins: Antibodies that combat diseases.

Enzymes

  • Function: Catalyze reactions without being consumed.
  • Specificity: Only specific substrates bind to the active site, forming enzyme-substrate complexes.
Induced Fit Model:
  • Enzymes change shape slightly upon substrate binding to fit snugly.
Factors Influencing Enzyme Activity:
  • Temperature: Low temperature slows activity; high temperature can denature enzymes.
  • pH: Altered pH affects enzyme shape and activity.
  • Inhibitors:
    • Competitive: Compete for the active site.
    • Non-competitive: Bind elsewhere, changing the enzyme's shape.
  • Concentration Effects:
    • Increase in enzyme concentration raises reaction rate until saturation.
    • Increase in substrate concentration raises reaction rate until all active sites are occupied.

Genes and Phenotypic Expression

  • Gene Expression Regulation: Controlled by transcription factors (TF) that can activate or silence genes.
  • Genotype and Phenotype Relationship:
    • Genotype: Complete set of genes.
    • Phenotype: Observable characteristics resultant from gene expression.
  • Environmental Influences: Factors like UV exposure affect gene expression leading to phenotypic changes (e.g., melanin production).
Epigenetic Markers:
  • Methylation prevents transcription by adding methyl groups to DNA.
  • Demethylation allows transcription to occur when methyl groups are removed.
  • Histone Modifications:
    • Histone methylation condenses chromatin, inhibiting transcription.
    • Histone acetylation loosens chromatin, enhancing transcription.

RNA Interference (RNAi)

  • RNAi inhibits translation by destroying mRNA.
  • Types of RNAi:
    • siRNA: Short RNA targeting specific mRNA.
    • miRNA: Can bind with multiple mRNA strands.
Epigenetic Changes and Diseases
  • Epigenetic markers can silence tumor suppressor genes, leading to cancer.

Mutations

  • Definition: Changes in DNA nucleotide sequence altering the genotype and phenotype.
  • Types of Mutations:
    • Point Mutations: Change in a single nucleotide.
    • Substitution:
      • Silent: No change in amino acid sequence.
      • Missense: Alters amino acid sequence.
      • Nonsense: Creates a premature stop codon.
    • Frameshift Mutations: Insertion or deletion of nucleotides shifts reading frame.
Mutagens and Their Effects
  • Examples include ionizing radiation, chemicals, and viruses that introduce mutations.

Consequences of Mutations

  • Germ Cells: Passed to offspring; can introduce new phenotypes.
  • Somatic Cells: Limited to tissue; not inherited.

Use of Genetic Information

  • DNA Extraction: Techniques to isolate DNA from cells.
  • PCR (Polymerase Chain Reaction): Amplifies DNA, critical for analysis.
    • Steps include denaturation, annealing, and extension.
  • Electrophoresis: Separates DNA fragments via gel; used after PCR.
  • DNA Sequencing: Determines nucleotide order; involves amplification and specific reactions to terminate sequence.
DNA Profiling
  • Employs Short Tandem Repeats (STR) to compare genetic samples.
Ethical Issues
  • Concerns about discrimination, misuse of genetic information, and privacy issues in genetic data collection.

Recombinant DNA and Cloning

  • Recombinant DNA: Formed by combining DNA from different sources.
  • Cloning: Involves integrating gene of interest into a plasmid, returned to a bacterium for replication.
  • Techniques for gene transfer include electroporation and microinjection.