B1.2 (what happens in cells?)

• what is each molecule of DNA?

  A chromosome
• how many chromosomes do most people have?

  46 chromosomes in each cell
• How many chromosomes do chickens have?

  78
• where do you inherit your chromosomes from?

  Half from your mother and half from your father
• what are the only organisms that share identical DNA?

  Identical twins and clones (organisms that are identical to their parents)
• what are genes?


  Short sections of DNA that code for characteristics such as eye colour
• what does a code in a gene cause?

  Specific proteins to be made, these particular proteins determine the cells function, for example, the protein haemoglobin is found in red blood cells, this binds to oxygen which allows red blood cells to transport it around the body. the combination of genes in an organism controls how the organism functions and what it looks like eg your blood group, whether you have freckles or not
• what is DNA made up of?

  2 strands, they are joined together by bases and then twisted together to form a double helix
• what are small units in DNA called?

  Nucleotides
• what is DNA a type of?

  Polymer
• what is each nucleotide made of?

  A sugar (deoxyribose) , a phosphate group and a base
• what holds 2 strands of DNA together?

  Bonds at the bases
• what shape is phosphate represented by?

  A circle
• what shape is deoxyribose represented by?

  A pentagon
• what shape is a base represented by?

  rectangle
• what are the 4 bases found in DNA?

  adenine, thymine, cytosine and guanine
• what can bases be represented by?


  A, T, C, G
• what is complementary base pairing?

  The pairing of nucleotide bases in DNA, where adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G)
• why can DNA not leave the nucleus of your cells?

  It is too big
• what happens instead of dna leaving the nucleus?

  A copy of the DNA is made called mRNA, it is like a single strand of DNA
• what does mRNA stand for?

  mRNA stands for messenger RNA
• what process is mRNA produced in?

  Transcription
• how does transcription take place?

  The DNA around a gene unzips so both strands are separated, 1 of the strands acts as a template. Complementary bases attach to the strand being copied so C joins to G and (uracil) U binds to A because there is no T in mRNA
• what happens once transcription has taken place?

  mRNA detaches itself from the DNA template and the DNA zips back up. mRNA is then small enough to move out of the nucleus and travels to ribosomes (subcellular structures) in the cytoplasm where the protein will be made
• what are proteins made from?

  Amino acids, different amino acids join to form different proteins
• what does the order of nucleotides in DNA determine?

  The type and order of amino acids which then determines which proteins are produced
• how are proteins made?

  Translation
• what happens as a new protein is made?

  1, the ribosome reads the nucleotides on the mRNA in groups of 3, these groups are called base triplets or codons and each triplet codes for a specific amino acid. Eg CGU codes for a different acid than ACG

  2, the ribosome continues to read the triplet code, adding more and more amino acids

  3, the amino acids join together in a chain , this is a protein
• what does the sequence of amino acids determine?

  How the protein will fold, each protein has a different shape which is important for protein function, many types of proteins are produced including enzymes and hormones
• what are enzymes made of and what are they?

  Made of proteins, are biological catalysts
• what does biological catalyst mean?

  They speed up a reaction without being used up themselves, once a reaction is finished they can be used to catalyse the same type of reaction again
• what reactions in your body are enzymes involved in?

  They build larger molecules from small ones (such as in protein synthesis) and break down large molecules into smaller ones (such as in digestion)
• what is the place where molecules of other substances bind to the enzyme?


  Active site
• why is the shape of the active site important?

  so that specific molecules can bind to the enzyme
• what is the molecule that binds to the enzyme called?

  Substrate
• why are enzymes highly specific?

  so they can only bind to one type of substrate molecule, the substrate must fit exactly into the active site or else the molecule cannot bind
• what is the lock and key hypothesis?


  Think of the enzyme being like a lock and the substrate being like a key, only one key will fit a lock and be able to turn a door which is the same way that enzymes work
• what happens when the substrate binds to the enzyme?

  An enzyme-substrate complex is formed, the reaction happens quickly and the products are released from the enzyme and the enzyme is then ready to catalyse another reaction
• how are enzymes used to build large molecules from smaller ones?

  The enzyme molecule and substrate molecules bind and the substrate molecules fit into the enzyme molecule's active site. a bond then forms between the substrate molecules and the product is made and the enzyme is free to catalyse another type of this reaction.
• how are enzymes used to break down large molecules into smaller ones?

  The enzyme molecule and the large substrate molecule bind, the large substrate molecule fits into the enzyme's active site and the bond in the substrate molecule breaks, the enzyme is now free to catalyse another reaction the same as this one and 2 smaller product molecules are made