B1.2 WHAT HAPPENS IN CELLS

• what does DNA stand for?

  Deoxyribonucleic acid
• true or false: every person's DNA is unique except for identical twins

  true
• where is dna contained?

  chromosomes
• where are chromosomes located in eukaryotic cells?

  nucleus
• is dna a polymer?

  yes
• what is the monomer of dna?

  nucleotides
• what are the 4 bases?

  adenine, thymine, guanine, cytosine
• dna runs anti-parallel.

  dna takes the form of a double helix.
• what are the parts of a nucleotide?

  phosphate

  deoxyribose sugar

  base
• what pairs with adenine?

  thymine
• what pairs with cytosine?

  guanine
• • The bases always pair up in the same way:
  • Adenine always pairs with Thymine (A-T)
  • Cytosine always pairs with Guanine (C-G)
  • This is known as ‘complementary base pairing’
• what is a gene?

  a section of DNA that codes for a particular protein
• • It is the particular order of bases in DNA that dictates which amino acids will be used to build the protein
  • A DNA sequence can be thought of as a collection of groups of three bases
  • Each three base grouping is called a triplet code
  • The triplet code contains all the information to code for a single specific amino acid
  • The order of bases (triplet codes) controls which type of amino acids will later be joined together to make a protein
• what are the two stages of protein synthesis?

  transcription and translation
• where does transcription take place?

  nucleus
• where does translation take place?

  cytoplasm
• what molecule is formed in transcription?

  mRNA (messenger RNA)
• • During transcription an intermediary molecule called mRNA (messenger RNA) is produced
  • The mRNA contains a copy (transcript) of the information stored in the gene
  •  mRNA is similar to DNA but much shorter and it is only single-stranded
  • To make the gene accessible, the two DNA strands in the double helix need to be unwound and separated (un-zipped)
  • mRNA can then be made using the DNA as a template to copy from
• • In eukaryotes the newly produced mRNA molecule moves out of the nucleus into the cytoplasm
  • During translation the mRNA is translated (decoded) to determine which amino acids are needed
  • Amino acids that match the triplet codes on the mRNA are joined together in the correct order
  • A long chain of amino acids is produced which forms into a protein 
• what is metabolism?

  the sum of all the reactions happening in a cell or organism, in which molecules are synthesised (made) or broken down
• • Enzymes act as biological catalysts to speed up the rate of a chemical reaction without being changed or used upin the reaction
  • Enzymes reduce the need for high temperatures
  • They are biological as they are made in cells
  • Enzymes are necessary to all living organisms as they allow all metabolic reactions to occur at a rate that can sustain life
• • Each enzyme has a specially shaped region known as an active site
  • The active site allows the enzyme to bind to the substrate
  • Once bound to the active site, the chemical reaction takes place
• The enzyme is like a lock and the substrate is the key that fits into the active site (like a keyhole).
• how does higher temp affect enzyme reactions?

  • Like any chemical reaction a higher temperature initially increases the rate of an enzyme-controlled reaction
  • The enzyme and substrate molecules have more kinetic energy, move faster and are more likely to collide
  • This leads to a faster rate of reaction
• how does too high temp affect enzyme reactions?

  • Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and the active site will lose its shape
  • the enzyme has been denatured irreversibly and will not go back into its original form
  • The substrate will not fit into the active site any more,
  • The enzyme can no longer catalyse the reaction so it stops
• what is the optimum temp for an enzyme inside the human body?

  37
• what is the optimum pH for human enzymes?

  pH 7
• • Moving too far away from the optimum pH will cause the enzyme to denature and the reaction it is catalysing will stop