Transcription and Translation

Decoding DNA’s Information

DNA carries instructions on how to make proteins Each protein’s instructions are in a gene

These proteins determine your traits We need to “photocopy” a gene in

order to produce the protein (trait)

RNA = Ribonucleic acid

Nucleic acid that is directly involved in the making of proteins The “photocopy” is called RNA Genes – segments of DNA nucleotides

that code for specific proteins DNA is in nucleus, but cell’s “machinery” to

make proteins is in the cytosol…how do we follow DNA’s instructions?

RNA vs. DNA Structure

3 structural differences between RNA & DNA: 1. RNA nucleotide has the sugar Ribose

(not deoxyribose) 2. RNA is single stranded 3. RNA uses the base Uracil (U) instead

of Thymine (T) a. A pairs with U instead

RNA…the “link” between DNA and Proteins

DNA must stay in the nucleus of a cell. Proteins are assembled at the ribosomes (in the

cytoplasm).

3 different types of RNA used to make proteins:1. mRNA = (messenger RNA) carries

information from DNA to Ribosomes.2. tRNA = (transfer RNA) reads the mRNA and brings the correct amino acid to build

the protein.3. rRNA = (ribosomal RNA) part of the Ribosome that grabs on to the mRNA

to position it for protein synthesis to occur.

Protein Structure

Made up of amino acids Polypeptide- string of amino acids 20 amino acids are arranged in

different orders to make a variety of proteins

Assembled on a ribosome

Replication

DNA

•DNA double helix unwinds•DNA now single-stranded•New DNA strand forms using complementary base pairing (A-T, C-G)•Used to prepare DNA for cell division•Whole genome copied/replicated

Transcription and Translation: An Overview (aka the Central Dogma)

DNA

RNA

Protein

Transcription

Translation

RNA vs. DNA

DNA Double stranded Deoxyribose sugar Bases: C,G A,T

RNA Single stranded Ribose sugar Bases: C,G,A,U

Both contain a sugar, phosphate, and base.

Transcription

The information contained in DNA is stored in blocks called genes the genes code for proteins the proteins determine what a cell will be

like

The DNA stores this information safely in the nucleus where it never leaves instructions are copied from the DNA into

messages comprised of RNA these messages are sent out into the cell to

direct the assembly of proteins

Transcription

The path of information is often referred to as the central dogma

DNA RNA protein

The use of information in DNA to direct the production of particular proteins is called gene expression, which takes place in two stages

transcription is the process when a messenger RNA (mRNA) is made from a gene within the DNA

translation is the process of using the mRNA to direct the production of a protein

Transcription

RNA forms base pairs with DNA C-G A-U

Primary transcript- length of RNA that results from the process of transcription

TRANSCRIPTION

ACGATACCCTGACGAGCGTTAGCTATCGUGCUAUGGGACU

WHY is TRANSCRIPTION Important?

It is needed to get the DNA message out of the nucleus so the ribosomes know what protein to make! 

Without transcription, the ribosome would have no idea what proteins the body needed and would not make any. 

You could NOT replace the hair that we loose every day; could NOT grow long fingernails; be able to fight off diseases; cells would fall apart because the proteins were not being replaced!!

TRANSCRIPTION

DNA is copied into a complementary strand of mRNA.

WHY? DNA cannot leave the nucleus. Proteins

are made in the cytoplasm. mRNA serves as a “messenger” and carries the protein building instructions to the ribosomes in the cytoplasm.

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Major players in transcription

mRNA- type of RNA that encodes information for the synthesis of proteins and carries it to a ribosome from the nucleus

Major players in transcription

RNA polymerase- complex of enzymes with 2 functions: Unwind DNA

sequence Produce primary

transcript by stringing together the chain of RNA nucleotides

mRNA Processing Primary transcript is

not mature mRNA DNA sequence has

coding regions (exons) and non-coding regions (introns)

Introns must be removed before primary transcript is mRNA and can leave nucleus

Transcription is done…what now?

Now we have mature mRNA transcribed from the cell’s DNA. It is leaving the nucleus through a nuclear pore. Once in the cytoplasm, it finds a ribosome so that translation can begin.

We know how mRNA is made, but how do we “read” the code?

Translation

Second stage of protein production mRNA is on a ribosome

Translation

To correctly read a gene, a cell must translate the information encoded in the DNA (nucleotides) into the language of proteins (amino acids) translation follows rules set out by the

genetic code the mRNA is “read” in three-nucleotide

units called codons each codon corresponds to a particular

amino acid

Translation

The genetic code was determined from trial-and-error experiments to work out which codons matched with which amino acids

The genetic code is universal and employed by all living things

Figure 13.2 The genetic code (RNA codons)

There are 64 different codons in the genetic code.

Translation Translation occurs in ribosomes, which

are the protein-making factories of the cell each ribosome is a complex of proteins and

several segments of ribosomal RNA (rRNA) ribosomes are comprised of two subunits

small subunit large subunit

the small subunit has a short sequence of rRNA exposed that is identical to a leader sequence that begins all genes

mRNA binds to the small subunit

13.2 Translation

The large RNA subunit has three binding sites for transfer RNA (tRNA) located directly adjacent to the exposed rRNA sequence on the small subunit these binding sites are called the A, P,

and E sites it is the tRNA molecules that bring amino

acids to the ribosome to use in making proteins

Figure 13.3 A ribosome is composed of two subunits

Translation

The structure of a tRNA molecule is important to its function it has an amino acid attachment site at

one end and a three-nucleotide sequence at the other end

this three-nucleotide sequence is called the anticodon and is complementary to 1 of the 64 codons of the genetic code

activating enzymes match amino acids with their proper tRNAs

Figure 13.4 The structure of tRNA.

Translation

Once an mRNA molecule has bound to the small ribosomal subunit, the other larger ribosomal subunit binds as well, forming a complete ribosome during translation, the mRNA threads

through the ribosome three nucleotides at a time

a new tRNA holding an amino acid to be added enters the ribosome at the A site

Translation

Second stage of protein production mRNA is on a ribosome tRNA brings amino acids to the

ribosome

tRNA

Transfer RNA Bound to one

amino acid on one end

Anticodon on the other end complements mRNA codon

tRNA Function

Amino acids must be in the correct order for the protein to function correctly

tRNA lines up amino acids using mRNA code

Translation

Before a new tRNA can be added, the previous tRNA in the A site shifts to the P site

At the P site, peptide bonds from between the incoming amino acid and the growing chain of amino acids

The now empty tRNA in the P site eventually shifts to the E site where it is released

Figure 13.5 How translation works

Translation

Translation continues until a “stop” codon is encountered that signals the end of the protein

The ribosome then falls apart and the newly made protein is released into the cell

WHY is TRANSLATION Important?

Makes all the proteins that the body needs 

Without translation, proteins wound not be made and we could not replace the proteins that are depleted or damaged

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SUMMARY of PROTEIN SYNTHESIS

DNA: TAC CTT GTG CAT GGG ATCmRNA AUG GAA CAC GUA CCC UAGA.A MET G.A HIS VAL PRO STOP

IMPORTANT CODONS

AUG = start translation (Met) UAA, UAG, UGA= stop translation

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Figure 13.6 Ribosomes guide the translation process

Ribosomes

2 subunits, separate in cytoplasm until they join to begin translation Large Small

Contain 3 binding sites E P A

Reading the DNA code

Every 3 DNA bases pairs with 3 mRNA bases

Every group of 3 mRNA bases encodes a single amino acid

Codon- coding triplet of mRNA bases

The Genetic Code

We now know the complete genetic code

64 “words,” or codons 61 represent an amino acid More than one codon for some amino

acids AUG is the start signal and represents

methionine UAG, UAA and UGA are the stop signals Universal Non-overlapping No spaces between codons

The language of amino acids is based on codons

1 codon = 3 mRNA nucleotides

1 codon = 1 amino acid

A U A U A U G C C C G C

How many codons are in this sequence of mRNA?

Using this chart, you can determine which amino acid the codon “codes” for!

Which amino acid is encoded in the codon CAC?

Find the first letter of the codon CAC

Find the second letter of the codon CAC

Find the third letter of the codon CAC

CAC codes for the amino acid histidine (his).

What does the mRNA codon UAC code for?

Tyr or tyrosine

Notice there is one start codon AUG. Transcription begins at that codon!

Notice there are three stop codons. Transcription stops when these codons are encountered.

Although we do have proofreading mechanisms in place, sometimes mutations occur and a protein is not translated properly.

Are there possible consequences to such errors in transcription? Well, errors in transcription will lead to the wrong codon and incorrect translation of amino acid and erroneous protein SO……. One disease we see as and example on this is…….

The Genetic Code

Which codons code for which amino acids?

Genetic code- inventory of linkages between nucleotide triplets and the amino acids they code for

A gene is a segment of RNA that brings about transcription of a segment of RNA

Transcription vs. Translation Review

Transcription Process by which

genetic information encoded in DNA is copied onto messenger RNA

Occurs in the nucleus

DNA mRNA

Translation Process by which

information encoded in mRNA is used to assemble a protein at a ribosome

Occurs on a Ribosome

mRNA protein

Chapter 14: Gene Technology

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Biotechnology

Genetic engineering is the use of technology to alter the genomes of organisms. Biotechnology includes genetic

engineering and other techniques to make use of natural biological systems to achieve an end desired by humans.

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The Cloning of a Gene Recombinant DNA Technology.

Uses at least two different DNA sources. Vector used to introduce foreign DNA into a host

cell. Plasmid.

Enzymes. Restriction enzymes cleave DNA. DNA ligase seals DNA into an opening

created by the restriction enzyme.

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Polymerase Chain Reaction

Polymerase Chain Reaction (PCR) can create millions of copies of a DNA segment very quickly. Can be subjected to DNA fingerprinting

using restriction enzymes to cleave the DNA sample, and gel electrophoresis to separate DNA fragments.

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Biotechnology ProductsProducts Effects and Uses

Anticoagulants Involved in dissolving blood clots; used to treat heart attack patients

Colony-stimulating factors Stimulate white blood cell production, used to treat infections and immune system deficiencies (e.g.; lupus)

Growth factors Stimulate differentiation and growth of various cell types; used to aid wound healing (e.g.; burn victims)

Human Growth Hormone (HGH) Used to treat dwarfism

Insulin Involved in controlling blood sugar levels; used in treating diabetes

Interferons Disrupt the reproduction of viruses; used to treat some cancers

Interleukins Activate and stimulate white blood cells; used to treat wounds, HIV infections, cancer, immune deficiencies

Biotechnology Products

New prostate cancer vaccine (FDA app. Apr 2010) Treats patients advanced form of prostate cancer.

Provenge : The series of three shots using a patient's own cells, and are designed to train the immune system to recognize and kill malignant cells.

Does NOT cure cancer, just make patients live longer (avg: 4 months)

$50-75K price range Still in testing stage

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Biotechnology Products

Transgenic Bacteria. Insulin. Human Growth Hormone.

Transgenic Plants. Pest resistance.

Higher yields.

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Genetic Engineering of Farm Animals

Transgenic Animals. The use of transgenic farm animals to

produce pharmaceuticals is currently being pursued.

Cloning transgenic animals. Dolly (1997).

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Genetic Engineering of Farm Animals

Production of bovine somatotropin (BST) 1994 Became commercially available for

dairy farmers to increase animals’ milk production

More money Although BST is functional, harmless,

and sanctioned by the FDA, much controversy exists over whether it is actually desirable.

Genetic Engineering of Crop Plants

Manipulation of the genes of crop plants to make them more resistant to disease from insects and improve crop yield. Cotton:

Over 40% of the chemical insecticides used for these crops

Bacillus thuringiensis (Bt) Harmful to caterpillars/tomato hornworms but

not harmful to humans 81% of U.S acreage is Bt cotton

Genetic Engineering of Crop Plants

60-70% of processed foods in the U.S. grocery shelves have genetically modified ingredients.

Table 14.2 (pg. 265) List of Genetically Modified Crops

Is eating genetically modified food dangerous?

EPA, FDA, and USDA approve food regulations in the U.S.

EPA approved EPSP enzyme (change in protein sequence) for human consumption

Bt (inhibits pests on cotton/corn crops) protein is approved for human consumption by the EPA

Benefits vs Risk

Benefits: Increased pest and disease resistance Drought tolerance Increased food supply Farmers make more money and keep

food cost down for consumers

Benefits vs Risk

Risk: Introducing allergens and toxins in

foods Antibiotic resistance Adversely changing the nutrient

content of a crop Creation of “super” weeds and other

environmental risk Unknown long-term health effects

So, do you think that it is safe to eat genetically modified foods?

This is for you to decide…