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Learn about the structure of RNA, the process of transcription and translation, the types of mutations that can occur, and how genes are regulated.
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Single stranded Ribose Sugar Phosphate group Base: Adenine, Uracil, Cytosine, Guanine Structure of RNA
Three Types of RNA Messenger RNA (mRNA) – transfers DNA code to ribosomes for translation. Transfer RNA (tRNA) – brings amino acids to ribosomes for protein synthesis. Ribosomal RNA (rRNA) – Ribosomes are made of rRNA and protein.
Transcription • RNA molecules are produced by copying part of the nucleotide sequence of DNA into complementary sequence in RNA, a process called transcription. • During transcription, RNA polymerase binds to DNA and separates the DNA strands. • RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of mRNA.
The Genetic Code • “Words” are 3 RNA sequences called codons. aaacgttcgccc DNA sequence uuugcaagcggg Complimentary mRNA uuu-gca-agc-ggg codons Amino acids Lysine – Arginine – Serine - Proline
Translation • During translation, the cell uses information from messenger RNA to produce proteins. • Transcription occurs in nucleus. • mRNA moves to the cytoplasm then to the ribosomes. tRNA “read” the mRNA and obtain the amino acid coded for. • Ribosomes attach amino acids together using a peptide bond, forming a polypeptide chain. • Polypeptide chain keeps growing until a stop codon is reached, creating a protein.
Mutations • Mutations are changes in the DNA code. • Gene mutations result from changes in a single gene. • Chromosomal mutations involve changes whole chromosomes.
Gene Mutation Point Mutation – Affect one nucleotide thus occurring at a single point on the gene. Usually one nucleotide is substituted for another nucleotide.
Gene Mutation Frameshift Mutation – Inserting an extra nucleotide or deleting a nucleotide causes the entire code to “shift”.
Gene Regulation • All (with a few exceptions) of an organism’s cells have the same DNA. Why then are there different cells? • The gene expression is different. In other words, cells ‘differentiate’ by expression of some genes and suppression of others. • Cells respond to their environment by producing differenttypes and amounts of protein. Can you think of a situation where this might happen?
Gene Regulation: Producing Proteins • Injury repair: cells can adapt to environmental changes such as an injury which requires repair by activating new genes • Cancer is a disease of uncontrolled and invasive cell reproduction. Cancers result when the genes responsible for coding the proteins that regulate cell division mutate and divide rapidly.
Questions • Which base in RNA is replaced by uracil? • How many mRNA codons are illustrated on the previous slide? • What is the name of the enzyme that creates the mRNA copy from DNA? • What is the name of the sugar in the mRNA nucleotides? • What is the mRNA transcript for the DNA sequence, TTACGC
Questions • What structure assists tRNA in translating the mRNA in the cytoplasm? • The role of tRNA is to carry a(n):
Gene Regulation • In simple cells (prokaryotic) lac genes which are controlled by stimuli, turn genes on and off. • In complex cells (eukaryotic) this process is not as simple. Promoter sequences regulate gene operation.
How Does it Work? • RNA Polymerase looks for a region on the DNA known as a promoter, where it binds and begins transcription. • RNA strands are then edited. Some parts are removed (introns) - which are not expressed – and other that are left are called exons or expressed genes.
Chromosomal Mutations • Deletion – Part of a chromosome is deleted • Duplication – part of a chromosome is duplicated • Inversion – chromosome twists and inverts the code. • Translocation – Genetic information is traded between nonhomologous chromosomes.
