OCR Gateway GCSE - Biology B3

OCR Gateway GCSE - Biology B3

1. DNA, proteins and mutations

   • Protein synthesis occurs on ribosomes in the cytoplasm
     • The code needed to produce a protein is carried from the DNA to the ribosomes by a molecule called mRNA
   • Proteins are: Made up from long chains of amino acids and can be structural, hormones, carrier molecules or enzymes
   • Mutations can lead to the production of many different proteins. This is because a change in bases in DNA can change the amino acid sequence.
   • Chromosomes are long coiled up molecules of DNA, divided up into regions called genes
   • Enzymes work by a lock and key mechanism
   • Enzymes activity is affected by pH and temperature. This is due to: lower collision rates at lower temperatures, denaturing at extreme of pH and high temperatures
   • Proteins are coded for by DNA: The base sequence codes for the order of amino acids, each amino acids is coded for three bases

2. Cell division and cell growth

   • In meiosis, the chromosome number is halved and each cell is genetically different
   • There are a number of differences between plant growth and animal growth
   • Growth can be measured by a change in wet mass, dry mass or length. each method has advantages and disadvantages but dry mass is the best measure
   • Gametes are produced by meiosis
   • New cells for growth are produced by mitosis
   • The new cells made by mitosis are genetically identical
   • Being multicellular allows organisms to: be larger, use cell differentiation
   • Undifferentiated cells called steam cells can develop into different cells, tissues and organs

3. Respiration and circulation

   • the symbol equation for aerobic respiration is:
   • Red blood cells carry oxygen around the body and are especially adapted for this function
   • The heart has four chambers and is part of a double circulatory system
   • Anaerobic respiration takes place during hard exercise when there is insufficient oxygen avaliable
   • Anaerobic respiration produces lactic acid, which: Builds up muscles causing pain and fatigue, acts as oxygen debt and has to be broken down in the liver after exercise
   • Arteries have thick elastic walls and carry blood away from the heart, Veins have large lumens and valves, and carry blood back to the heart

4. Changing genes and cloning

   • Gene therapy involves changing a person's genes to try and cure disorders
   • Genetic engineering can be used to produce useful products but raises some ethical issues

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