RNA and PROTEIN SYNTHESIS CHAPTER 13 RNA and PROTEIN SYNTHESIS

What is the genetic material responsible for our physical traits? DNA

What are the functions of DNA? Copying information Storing information Transmitting information

How does DNA store and transmit information? Genes contain coded DNA instructions for making proteins DNA stored in nucleus Proteins are made in the cytoplasm by ribosomes PROBLEM…how to get the code to the machinery? Another nucleic acid, RNA, translates the DNA message into protein

Central Dogma of Molecular Biology Describes flow of information from DNA to protein transcription translation RNA DNA Protein RNA is the link between DNA and proteins.

Analogy for central dogma The master plan has all the information needed to construct a building.

Analogy for central dogma But builders never bring a valuable master plan to the building site where it might be damaged or lost.

Analogy for central dogma Instead, builders work from blueprints, inexpensive disposable copies of the master plan.

Analogy for central dogma Master plan = DNA Building site = ribosomes (in cytoplasm) Blueprint copies = RNA

Comparison of DNA and RNA Consists of nucleotides Double stranded Deoxyribose as sugar Bases = A, C, T and G RNA Consists of nucleotides Single stranded Ribose as sugar Uracil (U) replaces T

RNA Builds Protein Messenger RNA – carries the instructions from DNA to cytoplasm on how to make the protein Ribosomal RNA – form ribosomes in cytoplasm to help build the protein Transfer RNA – delivers the amino acids needed to build the protein

Transcription (RNA synthesis) DNA  RNA Occurs in the nucleus Requires RNA polymerase Builds RNA strand Uses one strand of DNA as template Involves single gene Produces MANY RNA copies

Transcription (RNA Synthesis) How does RNA polymerase know where to start and stop? Sequences mark the start (promoter) and end (terminator) of a gene. RNA polymerase recognizes these sequences.

Transcription (RNA Synthesis) RNA editing: non-coding sections of the mRNA transcript (introns) are cut out. Remaining pieces (exons) are spliced together. What do you think would happen if introns were not removed from the pre-mRNA? Why do cells use energy to make a large RNA moelcule and then cut it up and throw pieces (introns) away? Biologists still don’t have a complete answer. But current understanding is that mRNA can be cut and spliced in different ways in different tissues making it possible for a single gene to produce severl different forms of RNA. Introns and exons may also play a role in evolution.

RNAi Video

Replication vs Transcription Replication copies the entire DNA Transcription only copies one gene Replication only makes one copy Transcription makes many copies BOTH involve complex enzymes BOTH follow complementary base pairing BOTH occur in the nucleus

If you were given the sequence of a DNA strand, could you figure out the sequence of the mRNA strand? Remember, U instead of T in RNA!!! For example: DNA T A C G C C C T A T T G A T mRNA ?? A U G C G G G A UA AC U A

RIBOSOMES and PROTEIN SYNTHESIS 13.2 RIBOSOMES and PROTEIN SYNTHESIS

Translation a.k.a. Protein Synthesis RNA  Protein

The language of protein synthesis Language of RNA = nucleotides Language of protein = amino acids 20 different amino acids found in proteins Sequence of amino acids influences the shape of the protein which determines its function Triplet code: three mRNA bases (codon) code for one amino acid

How is the order of bases in DNA and RNA translated into a particular order of amino acids in a protein? Genetic Code (mRNA codon translated into amino acid)

Genetic Code: Codon = a group of three nucleotide bases in the mRNA that codes for a particular amino acid RNA contains 4 bases Bases form a language with just four letters in the alphabet RNA is translated three “letters” at a time so that each “word” is three bases long and corresponds to one amino acid Each three letter “word” = codon

Genetic Code: (mRNA codon to amino acid) RNA contains 4 bases Bases form a language with just four letters in the alphabet RNA is translated three “letters” at a time so that each “word” is three bases long and corresponds to one amino acid Each three letter “word” = codon

Genetic Code: punctuation START codon signals the start of translation AUG also codes for methionine STOP codons signal stop of translation UGA, UAA, UAG Do not code for any amino acid

Genetic Code = common language UNIVERSAL – shared by all organisms REDUNDANT – more than one codon may code for the same amino acid Allows flexibility if mistakes are made

Quick Check A certain gene has the following base sequence: GACAAGTCCAATC Write the sequence of the mRNA molecule transcribed from this gene Divide you mRNA sequence into codons How many codons? What amino acid does each codon code for? How many amino acids?

The role of ribosomes in translation… Ribosomes use the sequence of codons in mRNA to assemble amino acids into protein chains

The role of transfer RNA (tRNA) in translation… Each tRNA molecule carries one kind of amino acid Anticodon on tRNA recognizes complementary codon on mRNA For example, tRNA for methionine has the anticodon UAC which pairs with the methionine codon (AUG)

Process of Translation Ribosome binds to mRNA mRNA codons attract complementary tRNA anticodons Ribosome forms a peptide bond between amino acids then breaks bond holding the amino acid to the tRNA Empty tRNA leaves; the ribosome pulls the mRNA exposing the next codon

QUICK CHECK… Remember, U instead of T in RNA!!! For example: DNA T A C G C C C T A T T G A T A mRNA ?? Amino acids tRNA

Central Dogma of Molecular Biology Describes flow of information from DNA to protein transcription translation RNA DNA Protein RNA is the link between DNA and proteins.

13.3 MUTATIONS

Mutations are changes in the DNA Gene mutations (single gene) Chromosomal mutations (multiple genes involved) mutated base

1. Gene Mutations Also known as point mutations because they occur at a single point in the DNA sequence Occur during replication Different types Substitutions Insertions and deletions

A. Substitutions One base is changed to a different base Only affect one amino acid Sometimes have no effect (silent) EX: changing mRNA codon from CCC to CCA Codon still specifies proline; SILENT EX: changing mRNA codon from CCC to ACC Replaces proline with threonine

B. Insertions and Deletions Frameshift mutations – “shift” the reading frame Effects are dramatic Can change every amino acid after the mutation

Frameshift Mutations

2. Chromosome mutations Changes in number or structure of chromosomes Occur during meiosis Four types Deletion (loss of all or part of a chromosome) Duplication (extra copy) Inversion (reverse in the direction of a chromosome) Translocation (one chromosome attaches to another)

Mutagens Chemical or physical agents in the environment that can cause mutations in DNA Include Pesticides, tobacco, environmental pollutants, UV light, X-rays

Harmful and Helpful Mutations Mutations can be harmful if… They cause drastic changes in the protein that is produced Defective proteins can disrupt normal function Ex: sickle cell anemia, some cancer The effects of mutations on genes vary widely. Some have little or no effect; and some produce beneficial variations. Some negatively disrupt gene function.

Harmful and Helpful Mutations Beneficial effects Variation produced by mutations can be highly advantageous to organisms in different or changing environments Responsible for evolution EX: pesticide resistance (bad news for humans but good news for mosquitoes) EX: human resistance to HIV The effects of mutations on genes vary widely. Some have little or no effect; and some produce beneficial variations. Some negatively disrupt gene function.