Chapter 11DNA and Protein Synthesis

Mrs. Svencer

11.1 Genes are made of DNA

Frederick and GriffithTransformation –bacteria with mice Strain A – pneumonia, fatal Strain B – harmless Heated strain A – harmless Mix heated strain A and strain B - death

Harmless bacteria - “transformed” Descendents were too - trait was passed on Heritable change

                                                                                                                  

                                                         Figure 11-1Griffith showed that although a deadly strain of bacteria could be made harmless by heating it, some factor in that strain is still able to change other harmless bacteria into deadly ones. He called this the "transforming factor."

Oswald Avery – focused on protein and DNA Heat strain A + strain B + protein-

destroying enzymes Offspring still transformed Protein not accountable for

transformation Heat strain A + strain B + DNA-

destroying enzymes Colonies did not transform Therefore, DNA = genetic material

Hershey and Chase – used viruses Virus = nucleic acid in a protein coat Bacteriophage = virus that infects

bacteria Batch 1

Labeled protein coats with radioactive sulfur

Radioactivity detected outside of the cells Batch 2

Labeled DNA with radioactive phosphorus Radioactivity inside cells Therefore, phage’s DNA entered bacteria Therefore, DNA is the hereditary material

                                                                                                             

                                                              Figure 11-4Hershey and Chase offered further evidence that DNA, not proteins, is the genetic material. Only the DNA of the old generation of viruses is incorporated into the new generation.

11.2 Nucleic Acids store information

DNA (deoxyribonucleic acid) Stores genetic information Built from nucleotides – 3 parts

1. Sugar – ring shape, “deoxyribose” 2. Phosphate group 3. Nitrogenous base – single or double

ring of C and N atoms

                                   

                              Figure 11-5A nucleotide has three components: a sugar, a phosphate group, and a nitrogenous base.

4 bases in DNA Pyrimidines: single rings

Thymine (T) Cytosine (C)

Purines: double rings Adenine (A) Guanine (G)

                                                                                

                                                  Figure 11-6DNA contains four different nitrogenous bases. Thymine and cytosine have single-ring structures. Adenine and guanine have double-ring

DNA Strands

Covalent bonds connect sugar to phosphate between nucleotidesSugar-phosphate “backbone”Nucleotides arrange in different 1. Numbers 2. Sequences (combinations are unlimited)

Rosalind Franklin and Maurice Wilkins

X-ray crystallography DNA = helix shape

Watson and Crick Made model of double helix using

Franklin’s pictures Twisted ladder

Complementary Base Pairs Purine + Pyrimidine

A-T (2 hydrogen bonds)G-C (3 hydrogen bonds)

11.3 DNA Replication – mechanism of inheritance (DNA – copying)

Template Mechanism 2 strands of double helix separate at

origins of replication Copying goes outward from origin in both

directions, making a “bubble” Each strand is a “template” for a new,

complementary strand Bases line up according to base-pairing

rules

                                               

                                                   Figure 11-9During DNA replication, the two strands of the original parent DNA molecule, shown in blue, each serve as a template for making a new strand, shown in yellow. Replication results in two daughter DNA molecules, each consisting of one original strand and one new strand.

                                                         

                                                 Figure 11-10DNA replication begins at origins of replication and proceeds in both directions, producing "bubbles." Eventually, all the bubbles merge, resulting in two separate daughter DNA molecules.

DNA polymerase (enzyme) links nucleotides together using covalent bonds DNA opens further as nucleotides added Eukaryotic DNA – many origins - speedy

New strands = daughter strands Fast and accurate

1 error / billion nucleotides

Review: DNA Replication occurs before a cell divides during the S phase of interphase of the cell cycle

11.4 Genes Provide Information for Making Proteins

Beadle and Tatum – orange bread mold Mutant strains unable to grow on

nutrient medium Lacked single enzyme needed to

produce a needed molecule Each mutant defective in a single gene “one gene-one enzyme” hypothesis –

one gene produces one specific enzyme NOW, “one gene – one polypeptide”

RNA is needed to make a protein

Nucleic Acid

RNA – ribonucleic acid

DNA – deoxyribonucleic acid

Sugar Ribose Deoxyribose

Nitrogenous bases

AUCG ATCG

Shape Single helix Double helix

Gene to Protein

1. Transcription - DNA to RNA Transcribed message (RNA) leaves

nucleus to cytoplasm

2. Translation – RNA to amino acid Codon = on RNA - 3 bases that code

for amino acid

Table of CodonsRNAFigure 11-1361/64 code for amino acids – some amino acids coded for by more than 1 codon Ex: UUU UUC – both code for

phenylalanine

3/64 – stop codons – end of each gene sequence

                                                       

                                                   Figure 11-13Each codon stands for a particular amino acid. (The table uses abbreviations for the amino acids, such as Ser for serine.) The codon AUG not only stands for methionine (Met), but also functions as a signal to "start" translating an RNA transcript. There are also three "stop" codons that do not code for amino acids, but signal the end of each

genetic message.

11.5 Two steps from Gene to Protein

Transcription: DNA to RNAMessenger RNA (mRNA) transcribed from DNA template – only 1 strand of DNA RNA nucleotides pair to complementary bases

– AUCG RNA polymerase - RNA nucleotides together RNA splicing – introns are removed and exons

are joined together Therefore, mRNA has a continuous coding

sequence

mRNA leaves nucleus

                                                                             

                                                         Figure 11-12Information flows from gene to polypeptide. First, a sequence of nucleotides in DNA (a gene) is transcribed into RNA in the cell's nucleus. Then the RNA travels to the cytoplasm where it is translated into the specific amino acid sequence of a polypeptide.

                                                     

                                             Figure 11-15In eukaryotes, the RNA transcript is edited before it leaves the nucleus. Introns are removed and the exons are spliced together before the "final draft" transcript moves into the cytoplasm where it gets translated.

Intron = noncoding region of mRNA

Exon = coding region of mRNA that is “expressed” or translated

Translation: RNA to protein

1. Start codon: AUG –translation begins2. Amino acids added one-by-one to a chain of amino acids A. tRNA (transfer RNA) translates

codons of mRNA to amino acids 1. tRNA molecule binds to appropriate

amino acid

2. tRNA recognizes, using base-pairing rules, codons in mRNA by its own complementary anticodon

Anticodon = 3 bases at one end of tRNA

3. Other end of tRNA = where amino acid attaches

4. An enzyme links tRNA to its amino acid, using ATP

   

                                                              

  

Figure 11-16During translation, tRNAs transport and match amino acids to their appropriate codons on the mRNA transcript. One end of the tRNA attaches to an amino acid. At the other end, a triplet of bases called the anticodon matches to the complementary mRNA codon.

B. occurs at ribosome 2 subunits – made of protein and rRNA

(ribosomal RNA) Small subunit – binding site for mRNA Large subunit – 2 binding sites for tRNA

1. “P” site (polypeptide) – holds tRNA carrying the growing polypeptide chain

2. “A” site (amino acid) – holds tRNA carrying next amino acid to be added to the chain

2 subunits hold mRNA and tRNA close together

C. ribosome connects new amino acid to the growing polypeptide chain

                                      

                                   Figure 11-17Ribosomes bring mRNA and tRNAs together during translation. Each ribosome has an attachment site for an mRNA transcript, and two sites for tRNAs.

3. Reaches stop codon UAA, UAG, UGA No amino acid at “A” site Translation stops

4. Completed polypeptide set free from tRNA by hydrolysis

11.6 Mutations

Mutation – any change in the nucleotide sequence of DNA Can be

Large regions of chromosomes Single nucleotide pairs

Base substitutions Replacement of 1 base or nucleotide

with another Sometimes no effect – “silent

mutation” Sometimes large effect Why?

Several amino acids have more than 1 codon

More disastrous mutations

Insertion Putting in an additional nucleotide

Deletion Taking away 1 nucleotide

Both insertion and deletion alter the triplet groupings

Now they code for new amino acids

Cause of mutations

Error during DNA replicationError during crossing over in meiosis

Mutagens – physical / chemical agents that cause mutations Ex: high-energy radiation, x-rays, UV

light Usually harmful, sometimes helpful

Ex: dark color in female tiger swallowtails

Mutations may be passed to offspring, if they occur in gametesUltimate source of genetic diversity