DNA & Protein Synthesis

Honors Biology

History

• Before the 1940’s scientists didn’t know what material caused inheritance.

• They suspected it was either DNA or proteins.

History

• A series of experiments proved that DNA was the genetic material responsible for inheritance.

Frederick Griffith

• Injected mice with different types of pneumonia bacteria

• Results showed some type of factor was transferred from killed cells to live cells

• Griffith called this transformation

Oswald Avery

• Repeated Griffith’s idea to find how transformation happens

• Result _ DNA was the factor responsible for transformation

History

• In 1952, Alfred Hershey and Martha Chase did an experiment using a virus that infects E. coli bacteria.

• The experiment proved that DNA and not protein is the factor that influences inheritance.

History

• Erwin Chargaff discovered the base pairing rules and ratios for different species.

• Adenine pairs with Thymine

• Cytosine pairs with Guanine.

History• Rosalind Franklin & Maurice Wilkins had

taken the 1st pictures of DNA using X-ray crystallization

This proved that DNA had a helical shape.

History• The Nobel Prize in Medicine 1962

Francis Harry Compton Crick

James Dewey Watson

Maurice Hugh Frederick Wilkins

Rosalind Franklin(Died of cancer 1958)

Wilkins has become a historical footnote and

Watson & Crick are remembered as the

Fathers of DNA

Watson Crick

DNADNA

OO=P-O O

PhosphatePhosphate GroupGroup

N

Nitrogenous baseNitrogenous base (A, T(A, T,, G, C)G, C)CH2

O

C1C4

C3 C2

5

SugarSugar(deoxyribose)(deoxyribose)

Nitrogen Bases

• 2 types of Nitrogen Bases– Purines

• Double ring–G & A

– Pyrimidines• Single ring

–C & U & T

PGA

CUT PY

DNA - double helixDNA - double helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

T A

DNA

• The genetic code is a sequence of DNA nucleotides in the nucleus of cells.

DNA• DNA is a double-

stranded molecule.

• The strands are connected by complementary nucleotide pairs (A-T & C-G) like rungs on a ladder.

• The ladder twists to form a double helix.

DNA

• During S stage in interphase, DNA replicates itself.

• DNA replication is a semi-conservative process.

DNA• Semi-conservative

means that you conserve part of the original structure in the new one.

• You end up with 2 identical strands of DNA.

DNA Replication

Step 1: Helicase unzips a molecule of DNA @ the hydrogen bonds between base pairs (breaking the H bonds).

Step 2: DNA polymerase joins individual nucleotides to produce a DNA molecule which is a polymer and it also “proofreads” each new DNA strand

Step 3: Ligase links the two sections together.

DNA

• Gene - a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color, etc.)

• A gene is a stretch of DNA.

DNA

• A mistake in DNA replication is called a mutation.

• Many enzymes are involved in finding and repairing mistakes.

RNARNA

OO=P-O O

PhosphatePhosphate GroupGroup

N

Nitrogenous baseNitrogenous base (A, (A, UU ,, G, C )G, C )CH2

O

C1C4

C3 C2

5

SugarSugar (ribose)(ribose)

RNA

• Function: obtain information from DNA & synthesizes proteins

3 differences from DNA

1. Single strand instead of double strand

2. Ribose instead of deoxyribose

3. Uracil instead of thymine

3 types of RNA

1. Messenger RNA (mRNA)- copies information from DNA for protein synthesis

Codon- 3 base pairs that

code for a single amino

acid. codon

3 types of RNA

2. Transfer RNA (tRNA)- collects amino acids for protein synthesis

Anticodon-a sequence of 3 bases that are complementary base pairs to a codon in the mRNA

3 types of RNA

3. Ribosomal RNA (rRNA)- combines with proteins to form ribosomes

Amino Acids

• Amino acids- the building blocks of protein

• At least one kind of tRNA is present for each of the 20 amino acids used in protein synthesis.

Transcription - mRNA is made from DNA & goes to the ribosomeTranslation - Proteins are made from the message on the mRNA           

Transcription

• In order for cells to make proteins, the DNA code must be transcribed (copied) to mRNA.

• The mRNA carries the code from the nucleus to the ribosomes.

Transcription

• RNA polymerase binds to DNA (only to promoters- sections that indicate it to bind on DNA molecule) & separates the DNA strands.

• Uses 1 strand as a template from which nucleotides are assembled into a strand of RNA.

• Signals (like promoters) tell it to stop when RNA is complete.

Translation

• At the ribosome, amino acids (AA) are linked together to form specific proteins.

• The amino acid sequence is directed by the mRNA molecule.

ribosome

Amino acids

Translation

• Begins when mRNA molecule in cytoplasm attaches to ribosome.

• It begins at AUG (the start codon) which always binds methionine (amino acid).

• The tRNA contains the anticodon whose bases are complementary to a codon on the mRNA strand.

• Then another tRNA comes into ribosome and binds the next codon to anticodon.

Translation

• The ribosome will then bind the two amino acids together, using peptide bonds, and breaks the bond between methionine and its tRNA.

• The tRNA floats away from the ribosome allowing ribosome to bind another tRNA.

• The ribosome will move along mRNA binding new tRNA molecules and amino acids.

Translation

• Process continues until ribosome reaches one of the three stop codons:– UAA– UAG– UGA

Then it releases the formed polypeptide and the mRNA molecule, completing translation.

Make A Protein

• DNA sequence

ATG TAC AAC AAG GTA ATT

• mRNA sequence

UAC AUG UUG UUC CAU UAA

Make mRNA

• mRNA sequence

UAC AUG UUG UUC CAU UAA

• tRNA sequenceAUG UAC AAC AAG GUA AUU

Make mRNA

• tRNA sequence

AUG UAC AAC AAG GUA AUU

• mRNA sequence

UAC AUG UUG UUC CAU UAA• Amino Acid sequence

met lys asp lys val stop

Mutations

• What causes mutations?– Can occur spontaneously– Can be caused by a mutagen

• Mutagen: An agent, such as a chemical, ultraviolet light, or a radioactive element, that can induce or increase the frequency of mutation in an organism.

Mutations

• Some mutations can:

• Have little to no effect

• Be beneficial (produce organisms that are

better suited to their environments)

• Be deleterious (harmful)

Mutations• Types of mutations

– Point Mutations : involves changes in one or a few nucleotides that occur at a single point in the DNA sequence.• Substitutions- one base changed to

another• Insertions- one base is inserted in the

DNA sequence• Deletions- one base is removed from

the DNA sequence

Mutations

• Example: Sickle Cell Anemia

Sickle Cell Mutation

• Mutation in the haemoglobin gene – Oxygen carrying protein found on red blood

cells.

Life expectancy is 50- 60 years old!

Mutations• Types of mutations

– Frame Shift Mutations: changes the “reading frame” of the genetic message, so that every codon beyond the point of insertion or deletion is read incorrectly during translation.

• Ex.: Crohn’s disease

Crohn’s Disease

• Bacterial products activate inflammation in digestive system causing– Diarrhea– Constipation– Cramps

• Mutation in a gene that produces kininogen protein.

• Mutation on Chromosome 16 too!

Insertion Deletion

Huntington’s disease

• A progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability.

• Mutations in HTT gene causes disease.

• HTT-produces huntingtin protein. – CAG trinucleotide repeat

Mutations• Types of mutations

– Chromosomal Inversions: an entire section of DNA is reversed.

– Ex.: Hemophilia

a bleeding disorder

DNA Repair

• A complex system of enzymes, active in the G2 stage of interphase, serves as a back up to repair damaged DNA before it is dispersed into new cells during mitosis.

Mutations

• Many (most) are neutral and have little or no effect.

• Polyploidy- a complete set of chromosomes fails to separate during meiosis, can produce gametes with:– 3N (Triploid)– 4N (Tetraploid)

Ex. Polyploid plants are larger and stronger than diplid plants.

Gene Regulation

• Only a fraction of the genes in a cell are expressed at a given time.

• Expressed gene- a gene that is transcribed into RNA.

How does cell decided which will be “expressed” and which will be “silent”?

Gene Regulation

• Certain DNA sequences serve as promoters for DNA-binding proteins to attach and they help to regulate gene expression.

• There are “regulatory sites” next to the promoter in which the action of these proteins determines whether a gene is turned on or turned off.

Gene Regulation

• Most Eukaryotic genes are controlled individually and have regulatory sequences

• Why is Gene Regulation Important?

Gene Regulation

• Regulation of gene expression is important in shaping the way a complex organism develops.

• Differentiation- cells don’t just grow and divide during embryonic development they become specialized in structure and function.

Gene Regulation

• Hox genes- a series of genes that control the differentiation of cells and tissues in the embryo. – A mutation in one of these “master control

genes” can completely change the organs that develop in specific parts of the body.

– Ex. Fruit fly mutation can replace fly’s antennae with legs growing on its head!

Human Genome Project

• The Human Genome Project is a

collaborative effort of scientists around the

world to map the entire gene sequence of

humans.

• This information will be useful in detection,

prevention, and treatment of many genetic

diseases.

DNA Technologies

• DNA technologies allow scientists to identify, study, and modify genes.

• Forensic identification is an example of the application of DNA technology.

Gene Therapy• Gene therapy is a technique for correcting

defective genes responsible for disease development.

• Possible cures for:– diabetes– cardiovascular disease– cystic fibrosis– Alzheimer's– Parkinson’s– and many other diseases is possible.

Genetic Engineering

• The human manipulation of the genetic

material of a cell.

• Recombinant DNA- Genetically

engineered DNA prepared by splicing

genes from one species into the cells of

a different species. Such DNA becomes

part of the host's genetic makeup and is

replicated.

Genetic Engineering • Genetic engineering techniques are used in

a variety of industries, in agriculture, in

basic research, and in medicine.

This genetically engineered cow resists infections of the udders and can help to increase dairy production.

Genetic Engineering • There is great potential for the development

of useful products through genetic

engineering• EX., human growth hormone, insulin, and pest-

and disease-resistant fruits and vegetables

Seedless watermelons are genetically engineered

Genetic Engineering • We can now grow new body parts and soon

donating blood will be a thing of the past,

but will we go too far?

Photo of a mouse growing a "human ear"