BIO-SEM1-'24-EXAM

• Acquired Immunity

  The specific defence mechanism involving the formation of antibodies and specialised cells in response to exposure to pathogens
• Deoxyribonucleic acid (DNA) is the genetic material
• Chargaff's rule


  • Adenine must pair with Thymine
  • Guanine must pair with Cytosine
  • The bases form weak hydrogen bonds
• Watson & Crick model of DNA

  • DNA has specific pairing between the nitrogen bases: Adenine-Thymine, Cytosine-Guanine
  • DNA is made of 2 long strands of nucleotides arranged in a specific "complementary" way
• DNA


  Deoxyribonucleic acid, made up of subunits called nucleotides consisting of a phosphate group, sugar, and nitrogenous base
• DNA structure


  • Two strands coiled in a double helix
  • Sides made of sugar and phosphate groups
  • Center made of nitrogen bases bonded by weak hydrogen bonds
• Complementary base pairing in DNA

  • Guanine-Cytosine require 3 hydrogen bonds
  • Adenine-Thymine require 2 hydrogen bonds
• Properties of DNA structure

  • The order of bases in one chain determines the other chain
  • The weak hydrogen bonds allow the strands to separate easily using enzymes
  • The strong covalent bonds are not easily broken, allowing for exact copying of the base sequences
• A gene is a section of DNA that carries the information for one polypeptide or one RNA molecule
• A chromosome consists of double stranded DNA and proteins
• The nucleus contains chromosomes
• Function of DNA


  DNA is a set of instructions that tells a cell which proteins to make, which are composed of chains of amino acids
• The code in DNA determines the order of amino acids in polypeptide chains (proteins)
• Each gene is a section of a DNA molecule which codes for one polypeptide chain
• Human non-sex cells have 46 chromosomes (23 pairs)
• Chromosomes contain many genes which code for the making of proteins
• The same genes are always found in the same location on the same chromosome
• Chromosomes can either be replicated or non-replicated
• DNA is replicated during cell division
• T and G with C

  Complementary base pairing
• Complementary base pairing


  • Unique feature of DNA that allows exact copying of DNA for DNA replication
• Chromosomes, genes, DNA


  • A section of DNA, which carries the information for one polypeptide, or one RNA molecule, is called a gene
  • A chromosome consists of double stranded DNA and proteins
  • The nucleus contains chromosomes
• Function of DNA


  • DNA is a set of instructions
  • It tells a cell which proteins to make
• Proteins


  Made up of chains of Amino Acids (AA's) (20 different types)
• The Genetic Material


  • The code in DNA determines the order of amino acids in polypeptide chains (proteins)
  • Each gene is a section of a DNA molecule which codes for one polypeptide chain
• DNA


  • Organised into structures called CHROMOSOMES
  • Chromosomes are sections of DNA wrapped around proteins
  • Human non-sex cells have 46 chromosomes (23 pairs)
  • Chromosomes contain many genes which code for the making of proteins
  • The same genes are always found in the same location on the same chromosome
  • Chromosomes can either be replicated or non-replicated
• DNA REPLICATION


  1. DNA is replicated during interphase - between cell divisions (The S phase of the cell cycle)

  2. The aim of DNA replication is to form identical copies of DNA so that cell division can occur

  3. This allows each new cell to contain the exact same information as the parent cell
• Free nucleotides are found in the nucleus
• DNA Replication - Part One: Expose the bases

  1. The double stranded molecule are "unzipped" into two single strands

  2. In order to unwind DNA, the interactions between base pairs must be broken

  3. This is performed by an enzyme known as DNA helicase

  4. DNA helicase disrupts the hydrogen bonding between base pairs to separate the strands into a Y shape known as the replication fork

  5. This area will be the template for replication to begin
• DNA Replication - Part Two: Pair Them Up

  1. Free floating individual nucleotides can pair up with the now exposed bases following the complementary base pairing rules

  2. The sugar and phosphate sections of the nucleotides bond together with the help of enzymes DNA polymerase
• DNA Replication - Part Three: Join it up

  1. Free floating individual nucleotides can pair up with the now exposed bases following the complementary base pairing rules

  2. The sugar and phosphate sections of the nucleotides bond together with the help of enzymes polymerase

  3. The result is two identical DNA molecules, each one in a double helix
• DNA Replication


  • Original (template) DNA strand
  • DNA Polymerase
  • DNA Polymerase
  • Free Nucleotides
  • Replication fork
  • Chromosomes
  • Helicase
• This process continues all the way up the DNA molecule
• Eventually, two new molecules are formed
• Semi conservative replication


  Each new molecule contains one old strand and one newly synthesised strand
• DNA


  • Chromosomes contain genes, sequences of nucleotide bases
  • These Genes code for polypeptides (proteins) or RNA molecules
  • Proteins have different structures that give them different functions and are used to build cells and do much of the work inside cells
  • The subunits of proteins are amino acids
• RNA molecules


  • Single stranded
  • Made of nucleotides: Ribose sugar, Phosphate, Bases (A, U, C, G) (A-U & C-G)
  • Types of RNA molecules: mRNA (messenger RNA) – copy of the gene, carry information to ribosome, tRNA (transfer RNA) –transfers amino acids to the ribosome, rRNA (ribosomal RNA) –part of the ribosome (the site of translation), miRNA (micro RNA) –involved in regulation of gene expression
• Protein synthesis stages


  1. Part 1: Transcription (copy genetic code, occurs in the nucleus)

  2. Part 2: Translation (build polypeptide chain based on genetic code)
• Transcription


  1. DNA -> pre-mRNA -> mRNA

  2. pre-mRNA: RNA copy of a gene from the coding strand (DNA codons), transcribed from the template strand through complementary base pairing

  3. RNA polymerase attaches to the DNA at the start of the gene

  4. The DNA is unwound and complementary RNA nucleotides bind to the template strand and are bound together

  5. This continues till the end of the gene

  6. The pre-mRNA detaches from the DNA and the DNA rewinds
• mRNA leaves the nucleus through its pores and goes to the ribosomes