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Human Cells Genes and proteins in health and disease 1 a. Protein structure and function What do you remember? Write down 10 words you associate with protein structure and function 2 What you need to know The elements that are found in proteins The bonds that build protein shape The variety and function of proteins 3 Protein structure The elements making proteins are C, H, O, N and often S Amino acids are joined with peptide bonds (polypeptides) Hydrogen bonds form between amino acids giving initial folding or coiling (sheets/helices) Sulfur bridges and other interactions between negative and positive charges More than 1 chain of amino acids can join together Non protein molecules can be associated with proteins 3 dimensional shape 4 5 Fibrous Globular 6 What type of protein? Collagen Somatotrophin Ligament Mucus Tubulin • What type of protein are these? • What do they do? • How is their structure related to their function? Testosterone Trypsin Endorphins Immunoglobulin 7 Types of protein Protein structure allows protein function Enzymes – globular . Folded proteins exposing active sites to binds specific substrate. Speed up biochemical reactions. Structural proteins – fibrous often globular but too. Cell membranes, muscle fibres Hormones – globular . Folded into specific shape to bind to receptors at specific sites. Regulate growth and metabolism Antibodies –globular Y shape . Bind to specific antigens Haemoglobin – conjugated. Protein with non protein molecule attached to transport oxygen 8 What do you know? Name the elements in proteins State the number of amino acids in human proteins Name the 3 types of bonds involved in protein structure Name the 3 broad groups of protein For each group of protein name an example For each protein example describe how its structure relates to its function Complete the questions from page 50 in the textbook 9 b. Mutations and their effect on protein function What do you remember? Write down 10 words you associate with mutations, proteins and their function 10 What you need to know Some types of gene mutations, what causes them and how they affect protein function Some types of chromosome mutations, what causes them and how they affect protein function or organism function 11 Mutations A change in an organisms genome Could be small with a single gene Could be larger change to chromosome structure or number Occur spontaneously, naturally, randomly, rarely Rate can be artificially increased by mutagenic agents e.g. UV light, X-rays, gamma rays, mustard gas etc. These mutations would be described as induced 12 Mutations and protein function Proteins are essential for life Proteins are structural and control the metabolism If a gene coding for a protein mutates, the amino acid sequence could be altered Faulty protein gives faulty structure or faulty metabolic pathway If a gene coding for a protein mutates, the protein may not be made at all Missing protein could mean non-functioning metabolic pathway 13 Gene mutations Mutations on a single gene would alter the nucleotide sequence Point mutations are the change in one nucleotide Could be deletion of one nucleotide changing all the following codons and hence amino acid sequence. Could be insertion of one nucleotide changing all the following codons and hence amino acid sequence. These two are both frameshift mutations Could be the substitution of one nucleotide for another altering only 1 codon and amino acid in the sequence 14 Gene mutations - Normal 15 Gene mutations - Deletion 16 Gene mutations - Insertion 17 Gene mutations - Substitution 18 Gene mutations Splice site mutations during processing of primary transcript mRNA the introns are removed. Exons join together by splicing to give coding for aa’s. Splicing is controlled by nucleotide sequences at splice sites on introns next to exons. If a mutation occurs at splice sites some introns may be left in and coded for in the mature mRNA 19 Gene mutations Splice site mutations 20 Gene mutations Nucleotide sequence repeat expansion A mutation that produces a repeat of a triplet of nucleotides (trinucleotide). This inserted repeat of the same triplet codon (often many times) stops the protein from functioning, due too many aa’s. 21 Gene mutations Nucleotide sequence repeat expansion 22 How do gene mutations change protein structure Substitutions alter only 1 codon so only 1 aa is affected When the code still makes sense but is different from original it is called a missense mutation. When the code causes the sequence to stop being read as the mutation produces a stop codon it is called a nonsense mutation. The polypeptide chain is shortened and the protein is not properly formed. 23 24 How do gene mutations change protein structure Splice site mutation (retaining introns) Modifying mRNA can give altered protein structure. Frameshift (seen in nucleotide insertions or deletions) These change all the codons after the change so all the amino acids change after it. The protein produced is likely to be non-functional 25 How do gene mutations change protein structure Nucleotide sequence repeat expansion This is producing multiple copies of the same codon. Can give extra amino acids of the same type. Can expand the sequence so much that protein fails to be produced. Most of the gene mutations produce genetic disorders that have adverse effects on the individuals who suffer from it. 26 Effects on Health Many gene mutations have an effect on the structure and function of proteins. These changes have an effect on health for e.g. Sickle cell disease (anaemia) PKU Duchenne muscular dystrophy Tay-Sachs syndrome Cystic fibrosis Beta thalessemia Fragile X syndrome Huntingdon’s disease missense missense nonsense frameshift insertion frameshift deletion splice site mutation nucleotide sequence repeat expansion nucleotide sequence repeat expansion 27 Chromosome mutations These affect the structure of a whole chromosome. These include: Deletion where part of a chromosome is lost Duplication where part of the chromosome is repeated Translocation where 2 or more chromosomes rearrange materials between them Because these are such large changes they are often lethal in their effect. 28 Chromosome deletion 29 Chromosome duplication 30 Chromosome translocation 31 What do you know now? What 2 effects can a mutation have on protein production? What are the 3 types of single gene mutation? What is a missense mutation? What is a nonsense mutation? What is a splice site mutation What 2 types of nucleotide changes are frameshift mutations? What is a nucleotide sequence repeat mutation? What are the 3 chromosome mutations? What happens in each of these mutations? 32 Consolidation Reading PPT, textbook or scholar and making own notes. Completing textbook questions page 50 and p62 Answer multiple choice questions chapter 4 33