DNA and PROTEIN SYNTHESIS

“Cracking the Code”

DNADNA• the blueprint of life

• contains the instructions for making proteins within the cell.

• Deoxyribonucleic Acid

• Found in the nucleus of the cell (mitochondria also have DNA)

The Shape of DNAThe Shape of DNA

• very long polymer

• a ‘twisted ladder’ or zipper

• called a double helix.

Structure of DNAStructure of DNA

• A 5 carbon SUGAR (deoxyribose)& phosphate backbone

• rungs that connect the backbones are nitrogenous bases

• Nucleotide = sugar + phosphate + nitrogenous base

DNA structure

Structure of DNAStructure of DNA

Anti parallel: one strand runs 5’ to 3’, the other runs opposite

4 DNA Bases4 DNA Bases • Purine base - double

rings.– Adenine– Guanine

• Pyrimidine base -single ring

– Thymine– Cytosine

Complementary PairingComplementary Pairing• complementary base pairs: normal pairing of nitrogenous bases is: 1 purine and 1 pyrimidine

• Adenine always and only binds with Thymine

A-T• Guanine always and only pairs with Cytosine

G-C

DNA ReplicationDNA Replication

• semi-conservative replication-new DNA molecule made of one parent and one newly replicated strand.

• In general a DNA molecule ‘unzips’ down the middle of the paired bases, 2 individual strands are made that will become the ‘templates’ for new complete DNA stands

The Steps for DNA Replication (during S-phase of Interphase):

1. Initiation starts at a specific necletide sequence, a group of enzymes called DNA helicases breaks hydrogen bonds between bases to unzip the double helix

2. Proteins bind to keep strands apart

3) RNA primers attach to a spot on the original DNA stand

4) DNA polymerase III – starts at where the primer attached to the DNA and makes new strand in 5’ to 3’ direction (always)

5) DNA polymerase 1 – removes primers and replaces with nucleotide

6) DNA ligase – joins DNA fragments

DNA makes DNA

DNA EditingDNA Editing• AMAZING!!! DNA has a spell check

• DNA polymerase cut out mismatched base, and replace it with the proper nucleotides.

Protein Synthesis

• Proteins -chains of amino acids.

• as small as 8 amino acids, and as large as over 50,000 amino acids.

• There are 20 amino acids

• One Gene One Protein Theory - production of each protein is controlled by one gene.

(Protein Function)

Functions:

- Pigments – eg. Melanin – protect or signal etc.

(Protein Function)

- enzymes – eg. Amylase – catalyze reactions

(Protein Function)

- movement – eg. Actin in muscle

(Protein Function)

• carriers – eg. Hemoglobin (oxygen)

(Protein Function)

channels – in membranes (eg. Porin)

(Protein Function)

• - receptors – cell recognition eg. CD4 receptor on WBC (AIDS)

Essential amino acids

-required for protein synthesis,

1. RNA is single stranded, DNA is double stranded

2. The 5 carbon sugar is ribose in RNA, deoxyribose in DNA

3. RNA uses the base uracil instead of thymine. Uracil binds with adenine. (A-U )

Ribonucleic acid (RNA)Ribonucleic acid (RNA)

3 Types of RNA3 Types of RNA

1. Messenger RNA (mRNA) • takes DNA code to the ribosomes where proteins

are made

2. Transfer RNA (tRNA) • brings the appropriate amino acids from the

cytoplasm to the ribosomes and strings them in order according to mRNA.

3. Ribosomal RNA (rRNA)

• not directly involved with protein synthesis

• makes the ribosomes in the nucleus

Protein Synthesis

Steps in Protein SynthesisSteps in Protein Synthesis 1. Transcription

• At a start sequence of neucleotides, the double stranded DNA opens up (unzipped by helicases again)

• RNA polymerase attaches to the promoter and builds the single stranded mRNA

• Stops at the termination sequence of nucleotides and mRNA detaches

• mRNA makes its way to the ribosome for translation

DNA-RNA

2. Translation-making the protein

• mRNA attaches between the two subunits of a ribosome which “reads” the mRNA

– mRNA is a codon (represents a 3 nucleotide sequence from the DNA that it just read)

• tRNA brings amino acids from the cytoplasm to the ribosome

– tRNA has an anticodon for an amino acid

ex) If mRNA codes UUU, t RNA anticodon is AAA and it will get the amino acid PHE

mRNA Codons

• 3 nitrogen bases that code for a specific amino acid –WHY 3?

• Start codon – starts protein synthesis, AUG which codes for methionine

• Stop codons – ends protein synthesis, UAA, UAG, UGA

• Intron – non-coding sequences

• Exon – coding sequences that make proteins

• Once translation is complete tRNA returns to the cytoplasm and mRNA is broken down.

Why Do Firefly’s Glow?

• What Makes a Firefly Glow?

DNA and Mutations • inheritable changes

• Spontaneous or caused by mutagenic agents– Ex) radiation, chemicals

• may be as simple as a single base pair

Basic Mutations:Basic Mutations:1. Substitution of nucleotide(s), usually mild mutation

created (but can be serious like sickle cell anemia)

2. Frameshift – changes the reading frame. A whole new sequence is read, usually leads to severe mutations. Framrshifts are caused by:a) Deletion of a nucleotide(s)b) Addition of extra nucleotide(s)

1. Translocation of a gene-DNA fragment switches location, often between different chromosomes. This is a very serious mutations (usually fatal)

BBC Education - AS Guru - Biology - Genes and Genetics - Genetic Code - Mutation

• Mutations in body cells often have little consequences compared to mutations of the germ cells (sperm or egg).

• A single mistake in the DNA of a sperm or egg cell would be repeated billions of times if that cell underwent fertilization to become a complete individual.

Transposons Transposons • are “jumping genes”,

DNA sequences that have the ability to move in / out of chromosomes, changing their location. May cause mutations or change amount of DNA

• http://www.dnalc.org/vshockwave/ac_ds_trans.dcr

Oncogenes and CancerOncogenes and Cancer Cancer -uncontrolled cell division from a changed

genetic code (uncontrolled mitosis)

Evidence:

1. Cancerous cells often display nitrogen base substitutions

2. Many known mutagens, are also known to cause cancer

3. segments of chromosomes extracted from cancerous mice transformed normal mouse cells into cancerous cells.

-genes called oncogenes cause cancer

Oncogenes and CancerOncogenes and Cancer

• oncogenes are present in normal cells, and do not always result in cancer

• oncogenes must be transposed to another site on the chromosome to be activated

The Ames TestThe Ames Test• To test for potential mutagens

• bacteria Salmonella typhimurium - unable to make histidine

• after the bacteria is exposed to a potential mutagen, it is grown in a culture without histidine.

• If it survives it has been mutated!

Biotechnology

• Biotechnology –biological systems used to produce a product.

• Genetic engineering –produces transgenic cells: foreign DNA inserted

• Recombinant DNA – DNA that comes from 2 or more sources.

• Vector –an organism (bacteria or virus) that carries and leaves its genetic material in a host cell. The host then replicates the vector’s genetic material.

• Plasmid – is circular DNA found in bacteria. This is often used as a vector in DNA recombination.

The process of creating recombinant DNA involves 2 types of enzymes:

1. Restriction Enzymes – (DNA scissors) cut the DNA strand at specific sites -palindromes- and often creates sticky ends

2. The now unpaired segments can be paired with complimentary nucleotides from a different strand of DNA

3. DNA ligase – is genetic glue that puts DNA strands back together.

• rDNA

Application• Insulin used to be harvested from pigs, but some

individuals did not tolerate it. • we are now able to use bacteria to produce

human insulin in large quantities. • is tolerated much better by patients.

• This procedure was first marketed in Canada in 1983!

Other Aspects of BiotechnologyOther Aspects of Biotechnology• Gene sequencing –determining the

specific location and composition of specific genes.

• The Human Genome Project -1990 2000: mapped our 30 000 genes (3 billion nucleotides)

• NOVA Online | Cracking the Code of Life | Sequence for Yourself

• RFLP – restriction fragment length polymorphism –cut DNA into pieces

• Gel Electrophoresis – separate the DNA pieces by size.

• DNA fingerprinting – identify an individual based on their

unique genetic code.

– homologous segments of DNA are similar but contain unique patterns of nitrogen bases

– identify individuals involved in crimes, paternity

DNA Fingerprinting

Misc. Technology

• Polymerase chain reaction –making billions of copies of a piece of DNA- PCR Animation

• Paternity Testing - Paternity Testing

• Gene Gun - Genegun1