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DNA, RNA, and Protein Synthesis

Chapter 12 and 13

Chap 12 Terms

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Do you know?

• What determines how a protein will function?

three-dimensional shape of the protein

• Why is it important that new cells have same DNA as the parent cell?

the cells may develop properties that would not be beneficial to the organism as a whole

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Objectives??• Relate how Griffith’s bacterial experiments

showed that a hereditary factor was involved in transformation

• Summarize how Avery’s experiments led his group to conclude that DNA is responsible for transformation in bacteria

• Describe how Hershey and Chase’s experiments led to the conclusion that DNA, not protein, is the hereditary molecules in viruses

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Discovery of DNA

• From his studies with pea plants, Mendel concluded that hereditary factors determine many of an organism’s traits. But what were these hereditary factors? How did these molecules store hereditary information? Scientists believed that if they could answer these questions, they could und4erstand how cell pass on characteristics to their descendants. The answers these questions began to emerge during an epidemic of pneumonia in London in the 1920s.

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Experiments

• Three experiments that led to the discovery of DNA and RNA

1. Griffith’s

2. Avery’s

3. Hershey-Chase experiments

Studies involved bacteria (bacteriophages or phages) and viruses (DNA head, protein body)

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Griffith’s experiments• 1928- studied bacteria Streptococcus

pneumoniae (pneumonia)

• Trying to develop a vaccine against virulent strain (disease-causing)

• Virulent bacterium is surrounded by a capsule made of polysaccharides that protect it from a body's defense systems

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Griffiths exp contTwo strains of bacteria

1. S strain – smooth-edged colonies, ill 2. R stain- rough colonies, lacks a capsule, does not cause pneumonia

• Had a series of 4 exp fig 10-2 (BIO)1. R cells mouse alive2. S cells mouse dies3. Kills S cells with heat mouse lives4. Kills S cells with heat and mix with R cells

mouse dies (transformation occurs)

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Griffiths exp cont

• Results or conclusion:Heat-killed virulent bacterial cells release a hereditary factor that transfers the disease- causing the healthy cells to be harmful

The transfer of genetic material from one cell to another is called transformation

(holt video)

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Heat Factor?

• DNA can tolerate temperature near 90’C without being altered. Proteins are denatured (broken down) at about 60’C.

• What effect temperature had on Griffith’s works?

A: The DNA was not altered and became incorporated into the DNA of the living bacteria

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DNA Technology• Griffith manipulated genes with out

knowing it. Today this manipulation of genes is known as genetic engineering or recombinant DNA Technology.

• Transformation is a modern-day genetic engineering technique.

• Examples: bacteria used to introduce foreign genes into plant cells, producing plants with desirable traits (Genetic modified)

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Avery's Experiments

• 1940’s wanted to test whether the transforming agent in Griffiths exp was protein, RNA, DNA

• Used enzymes separately to id which partResults• Cells missing protein and RNA able to transform

R cells into s cells mice die• Cells missing DNA did not transform mice

lived• DNA is responsible for transformation in

bacteria

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Radioactivity review?• Radioactive elements have unstable nuclei

that emit alpha and beta particles or energy as gamma rays.

• Emissions make it easier for scientists to detect and trace the path of the radioactive elements as they interact with other materials or transformed during metabolic processes

• (Radioactive isotopes, increase # neutrons, and the mass of the element)

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Hershey-Chase Experiment?They wanted to know if DNA or Protein was the hereditary

material viruses transfer when viruses enter a bacterium

• Bacteriophages or phages are viruses that infect bacteria (Holt video)

EXP:1. Used radioactive isotope sulfur (35S) to label protein

and radioactive isotope phosphorus (32P)to label DNA2. Infected the cells3. Blended separated the phage from bacteriaResults:Viral DNA and little protein entered bacteria concluded

that DNA is the hereditary molecule in the viruses(Honors 10.A)

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Key Questions:

• Evaluate the contributions of Franklin and Wilkins in helping Watson and crick discover DNA’s double helix structures

• Describe the 3 parts of a nucleotide

• Summarize the role of covalent and hydrogen bonds in the structure of DNA

• Relate the role of the base-paring rules to the structure of DNA

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DNA

• By the early 1950s, most biologist accepted DNA as the hereditary material. However, they still lacked an understanding of DNA’s structure or how this molecule could replicate, store, and transmit hereditary information and direct cell function. These mysteries would soon begin to unravel at Cambridge university in England.

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DNA is a double-stranded Helix• Pauling, Wilkins, Franklin- were first• They used x-ray diffraction• Watson saw an x-ray produced by Franklin and

was able to figure out the basic shape of DNA to be a helix (fig 10-5 bio)

• Watson and Crick began trying to construct a double helix w/ uniform diameter that would confirm Franklins data

• 1962 W and C received the Nobel Prize in Medicine and Franklin died in 1958 never to receive the award – currently recognized at Cambridge

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http://www.accessexcellence.org/RC/AB/BC/Rosalind_Franklin.phphttp://www.blinkx.com/video/rosalind-franklin-dna-discoveries-in-science-and-art/A3fUh_J7RZ77E7Njdd7zcA

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DNA Nucleotides

• DNA is a nucleic acid made of two long chains of Polymers made of monomers which is made of nucleotides

• Nucleotide is made of 3 parts

1. 5-carbon sugar (deoxyribose)

2. Phosphate group

3. Nitrogenous base

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Bonds hold DNA together• DNA looks like a spiral staircase• Covalent bonds and hydrogen bonds

Nitrogenous bases:4 types:

a. Purines- contain double ring of carbon

1. Adenine

2. Guanine

b. Pyrimidines- have a single ring of carbon

3. Thymine

4. Cytosine

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Complementary Bases

• 1949- Chargaff observed percentages of A= T, C= G

• Base-paring rules- single strand pairs up with second strand to make a double strand

• Complementary base pairs- A= T, C= G

• Base sequence- order of nitrogenous bases on a chain

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DNA model

• Looks like a ladder

• Sugar-phosphate is the handrails

• Base pairs are steps

• Draw in the complementary base pairs to:

AACCTGACTGGACAC

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DNA replication Key Questions

• Summarize the process of DNA replication• Identify the role of enzyme in the replication of

DNA• Describe how complementary base paring

guides DNA replication• Compare the number of replication forks in

prokaryotic and eukaryotic cells during DNA replication

• Describe how errors are corrected during DNA replication

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Q and A

Q: Why do you think gives DNA its stability even though the hydrogen bonds between the nitrogenous bases are easily broken?.

A: Strong covalent bonds connect the sugar and phosphate groups of the DNA backbone

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DNA Replication

• Watson and Crick’s discovery of the double helix structure of DNA caused great excitement in the scientific community. Scientists realized that this model could explain simply and elegantly how DNA can replicate exactly each time a cell divides, this is a key feature of hereditary material.

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How DNA Replication occurs

• Process by which DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission

• The two nucleotide strands of the original double helix separate along the strands

• Strands become templates to make new complementary strands

• Two identical DNA (double helix) separate and move to new cell during division

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Steps of replication1. Helicases- enzyme that separate the DNA

strands, move along the molecule breaking the H-Bond between the complementary nitrogenous bases, a Y-shaped region is formed called the replication fork

2. DNA polymerase adds complementary nucleotides

3. DNA poly completes strand and falls off4. DNA ligase links the pieces together 5. Get two identical DNA moleculesThis is called a semi-conservative replication-

keeps one of the original (conserved)

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Lesson OverviewLesson Overview Identifying the Substance of GenesIdentifying the Substance of Genes

Prokaryotic DNA Replication– In most prokaryotes, DNA replication

does not start until regulatory proteins bind to a single starting point on the chromosome. This triggers the beginning of DNA replication.

– Replication in most prokaryotic cells starts from a single point and proceeds in two directions until the entire chromosome is copied.

Lesson OverviewLesson Overview Identifying the Substance of GenesIdentifying the Substance of Genes

– Eukaryotic chromosomes are generally much bigger than those of prokaryotes.

– In eukaryotic cells, replication may begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied.

Eukaryotic DNA Replication

Lesson OverviewLesson Overview Identifying the Substance of GenesIdentifying the Substance of Genes

Chapter 13 Key Terms

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Protein Synthesis

Characteristics such as hair color are largely determined by genetic factors. But how does inheriting a particular form of a gene result in the appearance of a specific hair color? The structure of DNA helps explain how genes function in making proteins that determine traits in an organism.

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Misconception• Different cells, same DNA

You might think that because cells in the same organism appear different and have different functions, the cells must have different DNA.

The first fertilized egg undergoes DNA replication and then mitosis and then repeated to give every cell in the body the same DNA. (except for when crossing over takes place during meiosis to create gametes)

** other factors determine which genes are used for the cell’s specific function

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Key Questions• Outline the flow of genetic information in cells

from DNA to protein• Compare the structure of RNA To DNA• Summarize the process of transcription• Describe the importance of the genetic code• Compare the role of mRNA, rRNA, tRNA in

translation• Id the importance of learning about the human

genome

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Flow of genetic info• Gene- segment of DNA that is located on

a chromosome and codes for a specific trait

Process in Eukaryotic cells

DNA transcription RNA translation protein

1. Transcription- DNA acts as a template for the syn of RNA

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Flow of genetic info cont

2. translation- RNA directs the assembly of proteins

3. Protein synthesis- proteins are formed based on information in DNA and carried out by RNA (gene expression)

DNA (double stranded) RNA (single) Protein

* Proteins are responsible for protecting the body against infections and carrying oxygen in red blood cells

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RNA Structure and Function• RNA is a nucleic acid made up of

nucleotides4 major differences from DNA

1. contain the sugar ribose not deoxyribose2. contains the nitrogenous base uracil not thymine3. single stranded not double4. usually much shorter in length

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3 types of RNA

1. mRNA- messenger- single stranded molecules that carries the instructions from a gene to make a protein (carries a message)

2. rRNA- ribosomal- part of the structure of ribosome, ribosomes are made of rRNA and many proteins

3. tRNA- transfer- transfers amino acids to the ribosome to make protein

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TranscriptionProcess in which genetic instructions in a

gene are transcribed or rewritten into an RNA molecule

Steps1. RNA polymerase binds to promoter. The

promoter initiates transcription2. Adds free RNA nucleotides that are

complementary to the nucleotides on one of the DNA strands, DNA strands rewind

3. RNA poly reaches the terminal signal, makes the end of that gene, or a stop signal or stop codon

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The genetic code• Is the term that rules how a sequence of

nitrogenous bases in nucleotides corresponds to a particular amino acid

• The genetic code, three adjacent nucleotides in mRNA specify an amino acid in a polypeptide

• Each 3-nucleotide sequence in mRNA encodes for a amino acid or signifies a start or stop signal called a codon 10.1tab

(Start is AUG) (stop are UAA, UAG, UGA)

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Translation- making of protein

• Protein structure- one or more polypeptides, chains of AA linked by peptides bonds

• Over 20 AA found in proteins of living things

• AA are arranged to specific sequence

• Shape always equals function

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5 Steps of translation

1. Initiation- tRNA and mRNA bind, on the tRNA is the anticodon (3 nucleotides on RNA that complements codon in mRNA)

2. Elongation-the next AA binds to the codon, peptide bonds form between adjacent amino acids

3. Elongation cont- first tRNA leaves and leaves it AA, elongating the chain

4. Termination- stop codon is reached5. Disassembly- new polypeptide is released

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Human Genome

• 3.2 billion base pair in the 23 human chromosomes

• Take one person almost 10yrs to read the total sequence aloud

• Bioinformatics- uses pc to compare different DNA sequences, aids in interpretation

• Ability to treat diseases in the future

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Lesson OverviewLesson Overview Identifying the Substance of GenesIdentifying the Substance of Genes

Review Answers

1. Transcription

2. Nucleus

3. Stepsa. RNA Polymerase binds; DNA unwinds

b. mRNA starts to form

c. DNA and mRNA are released

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Lesson OverviewLesson Overview Identifying the Substance of GenesIdentifying the Substance of Genes

Review Cont:

1. Translation

2. Cytoplasm

3. Stepsa. initiation: tRNA binds to mRNA

b. Elongation: first peptide bond forms

c. Elongation: polypeptide chain grows

d. Termination: protein is complete

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DNA errors in replication

• Errors are rare- like typing this book 1000xs with out mistakes

• DNA polymerase have repair enzymes that proofread the strands and repair it

• Mutation are changes in the nucleotide sequence of DNA molecule

• Environmental factors can also disrupt or damage DNA

• Studying DNA replication is one good way to understand and treat some cancers

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Mutations• Change in the nucleotide-base sequence of a

gene or DNA molecule• Germ-cell: occurs in an organism’s gametes,

can be passed on to an offspring• Somatic-cell: body cell and can affect the

organism, skin cancer, leukemia, can not be inherited!!

• Lethal mutations- cause death before birth• Can mutations be beneficial to the individual?

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Chromosome MutationsTwo ways

1. change in structure of chromosome2. adding or loosing a chromosome

• Deletion- loss of a piecd of a chromosome due to breakage

• Inversion- segments breaks off, flips around and reattaches

• Translocation- breaks off and reattaches to non homologous chromosome

• Nondisjunction- chromosome fails to separate from its homologous during meiosis, get and extra copy (trisomy 21)

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Gene Mutations

• Point mutations- substitution, addition, or removal of single nucleotide

• Substitution- one nucleotide replaces another

• Frameshift mutation- it just shifts down- creates new amino acids

• Insertion mutations- addition of a gene and framshift occurs

• ATCGA

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Answers to Review

Replication

ATGCAGTACGGTGGGCTG

TRANSCRIPTION

AUG-CAG-UAC-GGU-GGG-CUG

TRANSLATION

MET START- GLU-TYR-GLY-GLY-LEU…..

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MUTATIONS

• TACGTCATGCCACCCGAC

1. Change C to G

substitution- no start codon

TAG AUC

2. Remove T- deletion

AUG- CAG-UCG-GUG-GGC-UG

START-LEU-SER-VAL-ALA- X

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