Chapter 10 Molecular Biology of the Gene

Section 10.1 – Experiments 1928 – English bacteriologist, Frederick Griffith

Section 10.1 – Conclusion from Griffith’s experiment The heat-killed S strain (mixed with the live R strain) was able to give its “deadly” properties to the R strain This is because the DNA from the S was taken in by the R. Result: R strain becomes deadly

Section 10.1 - Bacteriophages A virus that infects bacteria and turns it into a “phage-making factory”. Contains DNA inside of its head The head is made of protein

Section 10.1 – Experiments 1952 – American biologists, Hershey and Chase

Section 10.1 – Conclusion from Phage Experiment Phages leave their “head” or “shell” outside of a cell Phages insert their DNA into the cell The inserted “phage DNA” is what turns the cell into a phage-making factory

Section 10.2 – DNA

Section 10.2 - DNA The sides of a DNA molecule are composed of alternating deoxyribose sugars and phosphate groups

Section 10.2 – DNA Purines – Nitrogenous bases in DNA with a double ring structure

Section 10.2 – DNA Pyrimidines – Nitrogenous bases in DNA with a single ring structure

Section 10.2 – DNA Purines match up with pyrimidines

Section 10.2 – DNA vs. RNA DNA RNA Sugar = Deoxyribose Twisted into a double helix Double stranded A,T,C,G Found mainly in nucleus 1 Type RNA Sugar = Ribose Not shaped into a double helix Single Stranded A,U,C,G (has uracil instead of thymine) Found mainly in nucleolus 3 Types: mRNA, tRNA, and rRNA

Section 10.3 - Scientists Erwin Chargaff – 1949 – American Noticed that there were equal amount of adenine and thymine in DNA; also there are equal amounts of cytosine and guanine in DNA For example: if a DNA molecule is 30% adenine, it is also 30% thymine. Therefore it must be 20% cytosine and 20% guanine. (all percentages total 100%)

Section 10.3 - Scientists 2. Maurice Wilkins & Rosalind Franklin - 1952, England Took X- ray pictures of DNA to try to solve its structure

The actual DNA X-ray photo that Wilkins and Franklin took Section 10.3 Scientists The actual DNA X-ray photo that Wilkins and Franklin took

Section 10.3 - Scientists James Watson and Francis Crick 1953, England (Watson was American) Using the X-ray picture that Wilkins and Franklin took, Watson and Crick determined that DNA is a double helix structure They then built a model of DNA

Section 10.3 - Scientists Francis Crick James Watson

Section 10.4 – DNA Replication To “replicate” means to “copy” DNA has a special ability: with the help of enzymes, it can make an exact copy of itself. 1 DNA strand will make 2 “daughter” DNA strands

Section 10.5 – DNA Orientation DNA has two “sides” to it, like a ladder. One end of a side of the ladder is called the 5’ (prime) end. The other end of that same side is called the 3’ end. Please see the next picture to understand this concept.

Section 10.5 – DNA Orientation

Section 10.5 – DNA Orientation If the 5’ end is up, then the DNA molecule is oriented so that the deoxyribose looks like a pentagon with the point at the top If the 3’ end is up, then the DNA molecule is oriented so that the deoxyribose looks like an upside down pentagon

Section 10.5 – DNA Replication

Section 10.6 - Transcription To “transcribe” means to write something down In Biology, transcription means that DNA language is rewritten as mRNA language This occurs in the cell’s nucleus

Section 10.6 - Translation To “translate” means to take something that is in one language and convert it to another language In Biology, translation is taking the code that is in mRNA and converting it into a polypeptide/ protein Occurs in the cytoplasm

Section 10.7 - Codons A triplet code is what DNA and RNA have. The bases of each are “read” in threes. For example: ATT CCC GTG GAG TTA A codon is what the three letters are called collectively. For example: ATA is a codon. TTT is a codon. CG is not a codon.

Section 10.7 – Turning mRNA into a polypeptide/protein First, a “start codon” is found in the mRNA. The start codon for mRNA is always AUG. Take the amino acid chart, find “AUG” in the chart, and see what amino acid it corresponds to. If done correctly, AUG should correspond to methionine (met). Keep translating mRNA into amino acids until you reach a stop codon Can you find the 3 stop codons from the amino acid chart on the next slide?

Section 10.7 – The Amino Acid Chart

Section 10.9 - Transcription Name of enzyme that start transcription = RNA polymerase How RNA polymerase knows where to “start” transcribing DNA into mRNA RNA polymerase finds the “start codon” in DNA, which is TAC. TAC in DNA will make AUG in mRNA.

Section 10.9 – 3 Stages of Transcription Initiation – RNA polymerase finds the “start codon” in DNA (which is TAC) Elongation – RNA polymerase then continues along the DNA strand to make mRNA from the DNA code. Termination – RNA polymerase stops because it reaches a stop codon in the DNA.

Three types of RNA that are used in translation Sections 10.10, 10.11, and 10.12 Three types of RNA that are used in translation mRNA = messenger RNA. It is made directly from DNA tRNA = transfer RNA. It is attached to an amino acid and has an anticodon that matches up to mRNA’s codon. rRNA = ribosomal RNA. It is part of a ribosome (which is where translation occurs)

Pictures of the 3 RNAs

Section 10.14 - Translation Codon recognition = tRNA’s anticodon pairs up with mRNA’s codon Peptide bond formation = The polypeptide separates from the tRNA to which it was bound and forms a peptide bond with the amino acid on the new tRNA coming to the ribosome.

Section 10.14 - Translation 3. Translocation = The tRNA that is in the A-site of the ribosome moves to the P-site - The tRNA carries the growing polypeptide with it to the P-site

tRNAs move from the A-site to the P-site. Then the tRNA exits the ribosome from the E-site.

Picture of Translation

Section 10.16 Mutation – Any change in the nucleotide sequence in DNA For example: If an A gets replaced with a G or if a letter gets deleted altogether Reading Frame – A triplet grouping of the genetic message (a.k.a a codon) Mutagen – A physical or chemical agent that can cause a DNA mutation Radiation such as X-rays or UV light Chemicals such as cancer- causing agents

The Whole Picture