DNA / Protein Synthesis

History of DNA Research DNA – Deoxyribonucleic acid 1) Frederick Griffith (1928)- discovered that a factor in heat-killed, disease-causing bacteria can “transform” harmless bacteria into ones that can cause disease.

Griffith's Experiments Griffith set up four individual experiments. Experiment 1: Mice were injected with the disease-causing strain of bacteria. The mice developed pneumonia and died. Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another.

Experiment 2: Mice were injected with the harmless strain of bacteria Experiment 2: Mice were injected with the harmless strain of bacteria. These mice didn’t get sick. Harmless bacteria (rough colonies) Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Lives

Experiment 3: Griffith heated the disease-causing bacteria Experiment 3: Griffith heated the disease-causing bacteria. He then injected the heat-killed bacteria into the mice. The mice survived. Heat-killed disease-causing bacteria (smooth colonies) Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Lives

Heat-killed disease-causing bacteria (smooth colonies) Experiment 4: Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria and injected the mixture into the mice. The mice developed pneumonia and died. Harmless bacteria (rough colonies) Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Live disease-causing bacteria (smooth colonies) Dies of pneumonia

Heat-killed disease-causing bacteria (smooth colonies) Griffith concluded that the heat-killed bacteria passed their disease-causing ability to the harmless strain. Harmless bacteria (rough colonies) Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Live disease-causing bacteria (smooth colonies) Dies of pneumonia

Transformation  Griffith called this process transformation because one strain of bacteria (the harmless strain) had changed permanently into another (the disease-causing strain). Griffith hypothesized that a factor must contain information that could change harmless bacteria into disease-causing ones.

History of DNA Research 2) Oswald Avery (1944)- discovered DNA was responsible for transformation

History of DNA Research 3) Hershey and Chase (1952)- their studies supported Avery’s work by studying bacteriophage (a virus that infects bacteria)

History of DNA Research 4) Watson and Crick (1953)- first to develop a double-helix model of DNA

DNA DNA is found inside the nucleus of every cell in your body

DNA Structure DNA is made up of nucleotides. Nitrogenous Base Phosphate Sugar

Parts of a nucleotide A nucleotide contains three parts: 1) Phosphate group 2) 5-carbon sugar group (deoxyribose) 3) Nitrogenous bases (4 types) Adenine (A) Guanine (G) Purines (double rings) Cytosine (C) Thymine (T) Pyrimidines (single ring) To help you remember: CUT = PY

Chargaff’s Rule Erwin Chargaff (1949) discovered the base-pairing rules for nitrogenous bases: 1) A always pairs with T C always pairs with G 2) % A in DNA = % T in DNA % C in DNA = % G in DNA

Guanine Cytosine Adenine Thymine

Double Helix DNA molecule is composed of two long chains of nucleotides twisted and held together by hydrogen bonds in the center between the nitrogen bases

DNA Double Helix

In even in your smallest chromosome there are 30 million base pairs In even in your smallest chromosome there are 30 million base pairs. How does so much DNA fit in every tiny cell in your body?

Much more fits when you organize and fold it. DNA You fold it! Think about how much easier it is to pack your suitcase when everything is nicely folded. Can’t fit Much more fits when you organize and fold it.

DNA must condense (make itself smaller) by folding itself around proteins called Histones. When DNA wraps around Histones it forms tight coils and is called chromatin.

What are histones? What is Chromatin? Histones are proteins that DNA wraps around. What is Chromatin? Chromatin is what you call DNA when it is wrapped around the Histones.

Example: Histone DNA Double Helix Chromatin DNA around histones

Chromosomes When the chromatin forms coils and condenses it forms a chromosome. See Fig. 12-10 in your book.

DNA Double Helix Chromosomes Made up of chromatin Chromatin DNA around histones Histone =

http://www.biostudio.com/demo_freeman_dna_coiling.htm (dna coiling) DNA Double Helix  Chromatin  Chromosome DNA Double Helix DNA Chromatin DNA Chromosome http://www.biostudio.com/demo_freeman_dna_coiling.htm (dna coiling)

DNA Replication Occurs when cells divide. (Cell division)

DNA Replication DNA makes an exact copy of itself takes place inside the nucleus during S phase before cell division

Replication Each strand of the double helix of DNA serves as a template against which the new strand is made.

A compliments T T compliments A G compliments C C compliments G DNA Base Pairing Rules Sugar-phosphate Sugar-phosph phosphate A compliments T T compliments A G compliments C C compliments G G A C T T C A A G T

Replication Template strand Step 1: The hydrogen bonds between the double helix break and two strands separate. Each strand is called a template strand. Step 2: Two new complementary strands are formed following the rules of base pairing. The new strands are called complimentary strands. Compliment strand

How DNA Replication Works! DNA polymerase is an enzyme that adds the complimentary bases to the DNA template strand and also “proofreads” or checks that it is correct. DNA Polymerase T A

Semiconservative

Template Strand (original) CGTATCCGGAATTT GCATAGGCCTTAAA Replication Template Strand (original) CGTATCCGGAATTT The complimentary strand.. GCATAGGCCTTAAA

Template strand Complimentary Strand ACGGCAT TACGGCAT TGCCGTA ATGCCGTA

Complimentary If I have a strand that DNA sequence of CAT what would be on the complimentary strand? CAT GTA

RNA Ribonucleic acid Single strand made up of nucleotides contains three parts: 1) Phosphate group 2) 5-carbon sugar group (ribose) 3) Nitrogenous bases (4 types) Adenine (A) Guanine (G) Purines (double rings) Cytosine (C) Uracil (U) Pyrimidines (single ring)

Base-pairing in RNA 1) A always pairs with U 2) C always pairs with G

Types of RNA Type Function Messenger RNA (mRNA) Carries copies of instructions to make proteins Ribosomal RNA (rRNA) Is a part of ribosomes Transfer RNA (tRNA) Transfers each amino acid to the ribosome to help make proteins

Compare DNA and RNA 1) Sugars are different: Deoxyribose Ribose H OH OH OH H OH OH OH

Compare DNA and RNA DNA RNA 2) A, G, C,T A, G, C, U (A–T, C-G) (A-U, C-G) 3) Double stranded Single stranded 4) only 1 type 3 types

Protein Proteins are made of building blocks called amino acids. Proteins are different from one another by the sequence, or order, of their amino acids.

Protein There are 20 different amino acids. Thousands of proteins can be made from these amino acids because there are many different orders that they can be in.

Proteins are made in two steps: Transcription Translation

What is transcription? The process where mRNA is made from a DNA template Transcription happens in the nucleus

What is translation? Translation is the decoding of an mRNA message into a protein. Translation takes place on ribosomes in the cytoplasm

Transcription Translation

Transcription Protein synthesis begins when a strand of (A) DNA unravels. The code for producing a protein is carried in the sequence of the (B) bases in the DNA. Each group of three bases forms a codon, which represents a particular amino acid.

Transcription One of the unwound strands of DNA forms a complementary strand called (C) mRNA. This process is called transcription. It takes place in the nucleus of the cells.

Bases DNA mRNA

Post-transcriptional modification DNA is composed of coding and noncoding sequences Noncoding region = Introns Coding region = Exons (code for proteins) During transcription, introns are cleaved and removed, while exons combine to form useful mRNA

Post-transcriptional modification E I E I E initial DNA  introns cleaved pre-mRNA  exons combine final mRNA

Now look at the right side of the picture. The mRNA has moved into the cytoplasm, where it attaches to a (D) ribosome. A phase of protein synthesis called translation then begins. Ribosome mRNA

A (E) tRNA approaches the ribosome. At one end of this molecule are three bases known as an (F) anticodon. At the ribosome, each anticodon lines up with its complementary codon on the mRNA. tRNA Anticodon Codon Anticodon

This occurs according to base pairing. At the other end of tRNA, an (G) amino acid is attached. As the ribosome moves along the strand of mRNA, new tRNAs are attached. This brings the amino acids close to each other.

The amino acids are joined by peptide bonds, and the resulting strand is a protein.

Codon Chart To determine which amino acid we choose we use this chart: CODON AMINO ACID AGU AGC GGU

What are mutations? Mutations are changes in the DNA sequence that affects the genetic information

Types of mutations: Gene mutations result from changes in a single gene Chromosomal mutations involve changes in whole chromosomes

Gene mutations: Point mutations – affect only one nucleotide because they occur at a single point Include substitutions, additions, and deletions Frameshift mutations – when a nucleotide is added or deleted and bases are all shifted over, leaving all new codons. Include additions and deletions Substitutions don’t usually cause a frameshift

Substitutions DNA mRNA Amino acids Original TAC GCA TGG AAT AUG CGU ACC UUA Met – Arg – Thr – Leu Substitution TAC GTA TGG AAT AUG CAU ACC UUA Met – His – Thr - Leu One base change

Insertions DNA mRNA Amino acids Original TAC GCA TGG AAT AUG CGU ACC UUA Met – Arg – Thr – Leu Insertion TAT CGT ATG GAA T AUA GCA UAC CUU A Ile – Ala – Tyr - Leu Many base changes

Deletions

Chromosomal mutations: Include deletions, duplications, inversions, and translocations.

Deletions involve the loss of all or part of a chromosome.

Duplications produce extra copies of parts of a chromosome.

Inversions reverse the direction of parts of chromosomes.

Translocations occurs when part of one chromosome breaks off and attaches to another.

Significance of Mutations Many mutations have little or no effect on gene expression. Some mutations are the cause of genetic disorders.