BIOL10221 2024 Molecular Biology Lecture 2 - Genes PDF

BIOL10221 Molecular Biology Module 1 - Lecture 2: Genes Ray O’Keefe [email protected] What will we cover? How lengths of DNA are described Definition of genes and their structure Description of gene families and how they arise Why is it important? Genes are the functional units...

BIOL10221 Molecular Biology Module 1 - Lecture 2: Genes Ray O’Keefe [email protected] What will we cover? How lengths of DNA are described Definition of genes and their structure Description of gene families and how they arise Why is it important? Genes are the functional units of the genome Genes code for the proteins and RNAs that are required for cell function Gene families play a role in the evolution and diversity of multicellular organisms BIOL10221 Module 1 - Lecture 2 2 A gene is a segment of a DNA molecule The DNA sequence within this segment contains biological information BIOL10221 Module 1 - Lecture 3 2  How long is a gene? The unit of length of a DNA molecule is the base pair (bp) 1 bp ATGACTACGCAGTCAGTGC ||||||||||||||||||| TACTGATGCGTCAGTCACG = 1 kilobase pair (kb) 3,200 Mb haploid Human gen = 1 megabase pair (Mb) 6,400 Mb diploid Huma BIOL10221 Module 1 - Lecture 4 2 How long is a gene? Shortest genes = about 100 bp (example: tRNAs) Longest genes = about 2,400,000 bp (example: human muscle protein dystrophin) Do the longest genes contain 24,000 times more biological information than the shortest genes? NO they don’t!! BIOL10221 Module 1 - Lecture 5 2  Many genes are discontinuous They are split into: exons – contain information to make a protein introns – information not needed to make a protein Exon 1 Exon 2 Exon 3 Intron 1 Intron 2 Average human gene contains 8 introns and 9 exons Mean intron length is 3365 bp, mean exon length 145 bp In many genes the introns can make up almost 90% of the total length BIOL10221 Module 1 - Lecture 6 2 What is the information carried by a gene? This is the nucleotide sequence Part of the human CFTR gene (cystic fibrosis transmembrane conductance regulator) BIOL10221 Module 1 - Lecture 7 2 The information is read by the process called gene expression BIOL10221 Module 1 - Lecture 8 2 Proteins and RNAs are the functional end products of gene expression Proteins play many roles in the cell BIOL10221 Module 1 - Lecture 9 2 The information is read by the process called gene expression BIOL10221 Module 1 - Lecture 10 2  RNAs not made (translated) into proteins also play important roles in the cell More noncoding RNAs are still being discovered! BIOL10221 Module 1 - Lecture 11 2 Some genes are unique – there is just one copy of that gene Other genes occur in families In a simple multi-gene family, all the genes are the same These are ones where the gene product is needed in large amounts examples are the ribosomal RNA genes ribosomal RNAs are parts of ribosomes, the structures that make proteins in the cell BIOL10221 Module 1 - Lecture 12 2 In a complex multigene family, the genes are not identical but have similar DNA sequences They code for similar but non-identical proteins Provides proteins with slightly different functions which allows increased organismal complexity The human globin genes are examples, globin proteins bind and transport oxygen BIOL10221 Module 1 - Lecture 13 2 The human globin genes form two complex multigene families The alpha-globin genes are on chromosome 16 The beta-globin genes are on chromosome 11 = Zeta = Epsilon = Gamma = Delta BIOL10221 Module 1 - Lecture 14 2 The hemoglobin genes are expressed at different stages in human development = Zeta = Epsilon = Gamma = Delta BIOL10221 Module 1 - Lecture 15 2  The genes in a multigene family arise by gene duplication After duplication, the sequences of the genes gradually change so the members of the gene family have slightly different sequences BIOL10221 Module 1 - Lecture 16 2  The greater the time that has passed since the duplication, the more differences we usually see between the pair of genes BIOL10221 Module 1 - Lecture 17 2 The molecular clock is a measure of the rate at which the sequence of a gene changes We can use the molecular clock to work out when a pair of genes were formed by duplication BIOL10221 Module 1 - Lecture 18 2 We can make an evolutionary tree of all the globin genes BIOL10221 Module 1 - Lecture 19 2 Some genes have lost their function they have changed in such a way that their nucleotide sequence no longer makes sense they are called pseudogenes There are four pseudogenes in the alpha-globin family and one in the beta-globin family = Psi = Theta BIOL10221 Module 1 - Lecture 20 2 Resources Reading for Module 1 – Genes and Gene Structure Introduction to Genetics, A Molecular Approach BROWN, Chapter 3 pages 31–37, 40–46 ALBERTS, Pages 239, 232, 267-271, 304-305 Blackboard PDF files with Reading, Objectives, Terms, Questions and Answers BIOL10221 Module 1 - Lecture 21 3  BIOL10221 Molecular Biology Module 1 - Lecture 2: Genes Ray O’Keefe [email protected]