Topic 2 - A Level Edexcel Biology Exam with Solutions

Diffusion - passive movement of molecules What is diffusion dependent one? - concentration, thickness of diffusion pathway, surface area How are lungs adapted for efficient gas exchange - Lots of alveoli - large surface area Capillary endothelial - one cell thick, short diffusion pathway Breathing in and out maintains a concentration gradient Fick's Law of Diffusion - surface area x concentration gradient / diffusion pathway What are proteins made from? - long chains of amino acids What is a polypeptide? - long chain of amino acids How does a polypeptide form? - peptide bond and a condensation reaction What determines the shape of a protein? - sequence of amino acids and the size of the r group Four structural levels of proteins - primary, secondary, tertiary, quaternary What is a primary structure? - sequence of amino acids in a polypeptide chain What is a secondary structure? - the polypeptide chain folds and there is hydrogen bonds between amino acids in chains What are the two secondary structures - alpha helix and beta pleated sheet Alpha helix - the r group is small, the chain coils, hydrogen bonds Beta pleated sheet - r group is bulky, chain folds on itself, hydrogen bonds between the amino acids What is tertiary structure? - secondary structure folds into a unique shape What are the different bonds that can occur in tertiary structure? - hydrogen, ionic, disulfide What is quaternary structure? - several different polypeptide chains held together by bonds What are examples of quaternary structures - Globular - haemoglobin (functional) Fibrous - collagen (structural) What is the arrangement of groups in a 3d+ structure - Hydrophobic place themselves on the inside and hydophilic on the outside