DNA and Protein Synthesis

• What are nucleotides comprised of?

  Phosphate, sugar, and nitrogenous base
• What is the key role of DNA?

  To contain the genetic instructions for the development and function of an organism
• Structure of DNA


  A double-stranded helix formed by twisting two complementary strands of sugar-phosphate and nitrogenous bases
• What are the four bases in DNA?

  Adenine, thymine, cytosine and guanine
• How do the bases in DNA pair?

  A always pairs with T and C always with G.
• The order of bases in a gene decide the order of amino acids in a protein
• The order of bases in all of an organism‘s DNA is called its genetic code
• Genetic variation occurs when there are differences between individuals in their genes or chromosomes
• Each base on one template strand attracts a complementary base from the other template strand
• DNA replication is the process whereby one molecule of DNA produces another identical copy
• In DNA replication, the original DNA unwinds into two separate strands which act as templates to produce new complementary strands
• Ribonucleic acid (RNA) is made up of ribose sugar, nitrogenous bases and phosphate groups
• There are three types of RNA: messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA)
• Protein synthesis involves transcription and translation
• Transcription is when mRNA is produced by reading the sequence of nucleotides in DNA
• Translation is when amino acids join together to form proteins using tRNA and rRNA
• The genetic code consists of codons that specify particular amino acids or stop signals
• Homozygous alleles

  If the alleles for a characteristic in a chromosome pair are the same, the alleles are said to be homozygous
• Heterozygous alleles

  If the alleles for a characteristic in a chromosome pair are different, the alleles are said to be heterozygous
• Punnett Squares - The Results

  • Can represent the results as a percentage, fraction, probability or ratio
  • Can use the ratio to make a conclusion about how many children in a family will have a feature
• Y chromosome

  • Responsible for developing the male sex hormone
  • Contains the SRY gene - sex determining region of the Y chromosome
• How is DNA structured?

  In a double helix. The sides are made out of sugar and the rungs are comprised of complementary bases
• The sequences of bases along a DNA molecule forms the genetic code
• Each amino acid is coded for by a sequence of 3 bases in the gene called a triplet
• The amino acids are joined together to make various proteins, depending on the order of bases in the gene
• The properties of each protein are determined by the particular amino acids it contains and the order they are in
• What is protein synthesis?

  Protein synthesis is the process by which cells build proteins using the instructions encoded in DNA.
• The cell needs to make a copy of the information contained in the genes and take the copy to the cytoplasm where proteins are synthesised. This is because DNA can’t leave the nucleus of the cell because it is too large.
• What is mRNA?

  mRNA is a polymer of nucleotides but it is shorter and only a single strand. mRNA also uses Uracil (U) instead of Thymine as a base. U pairs with A
• Transcription occurs in the nucleus
• Translation occurs in the cytoplasm
• During transcription, RNA polymerase moves along the template strand of DNA and joins the complementary bases together to form an mRNA molecule
• In translation, tRNA brings amino acids into the ribosome and links them together to form a polypeptide chain
• Amino acids join together to form a polypeptide chain during translation
• What causes DNA to mutate?

  Can be caused by substances (eg radioactive substances) and ionising radiation but most are caused by errors when copying the DNA
• Human Genome

  The complete set of genetic information encoded in the DNA of a human being, serving as a blueprint for development and function of the entire human body.
• Chromosome

  A thread-like structure that carries genes and non-coding regions, found in the nucleus of eukaryotic cells.
• What are gametes?

  Gametes are the egg cell in females and sperm cells in males.
• What is the function of gametes?

  Reproduction
• Gametes contain the genetic information that will be passed on from each parent.