Biology: DNA and Protein Synthesis Quiz

DNA and Protein Synthesis

• DNA and RNA are the two main genetic materials in living organisms.
• DNA is a double helix composed of deoxyribonucleotides, while RNA is single-stranded.
• RNA types include mRNA (messenger), rRNA (ribosomal), and tRNA (transfer).
• DNA base pairs: Guanine (G) with Cytosine (C), Adenine (A) with Thymine (T).
• RNA base pairs: Adenine (A) with Uracil (U), Guanine (G) with Cytosine (C).
• DNA holds the genetic information for all biological structures and functions.
• The Central Dogma explains the flow of genetic information in biological systems (DNA to RNA to protein).

DNA Replication

• DNA replication is the process of making identical copies of a double-stranded DNA molecule.
• It ensures genetic information is passed on.
• Steps of replication:
  • DNA strands separate (Helicase breaks hydrogen bonds).
  • RNA primers bind to the DNA strands.
  • DNA nucleotides are added to the template strands (using DNA Polymerase).
  • Two identical DNA molecules are formed (semiconservative).

Transcription

• Transcription is the process of copying a DNA segment (gene) into mRNA.
• mRNA carries the genetic information from the nucleus to the cytoplasm.
• Steps of transcription:
  • RNA polymerase binds and unzips the DNA.
  • RNA polymerase adds RNA nucleotides complementary to the DNA strand.
  • mRNA separates from the DNA, which reforms.
  • mRNA moves to the cytoplasm.

Translation

• Translation is the process of converting the mRNA sequence into a protein.
• Ribosomes read mRNA in codons (3 bases at a time).
• Each codon codes for a specific amino acid.
• Steps of translation:
  • mRNA binds to a ribosome.
  • tRNA molecules, carrying amino acids, approach the ribosome.
  • tRNA anticodon pairs with mRNA codon (initiation complex).
  • Amino acids are linked together by peptide bonds.
  • The process continues until a stop codon is reached.
  • Polypeptide chain (protein) is released.

Mutations

• Mutations are changes in DNA sequence.
• Mutations can affect organism growth and development.
• Mutagens (e.g., harmful chemicals, radiations) cause mutations.
• Mutations can be in reproductive (heritable) or somatic cells.
• Types of mutations:
  • Gene mutations (changes within genes):
    • Deletion (loss of DNA segment).
    • Duplication (extra copies of gene/chromosome).
    • Translocation (chromosome segments exchange position).
    • Inversion (chromosome segments reverse position).
  • Chromosomal mutations (changes in chromosome structure).

Examples of Chromosomal Disorders

• Cri du chat syndrome: Deletion in chromosome 5; high-pitched cry, characteristic facial features, intellectual disability.
• Down syndrome (Trisomy 21): Extra copy of chromosome 21; decreased muscle tone, heart defects, intellectual disability.
• Edward syndrome (Trisomy 18): Extra copy of chromosome 18; severe intellectual and motor disability, multiple congenital anomalies, short lifespan.
• Jacobsen syndrome (11q deletion): Rare disorder; variable intellectual ability, speech problems, bleeding disorder.
• Klinefelter syndrome (XXY): Male disorder; underdeveloped sexual characteristics, tall stature, possible speech delay.
• Turner syndrome (XO): Female disorder; underdeveloped sexual characteristics, short stature, low hairline, possible heart and kidney problems.