Transcription Translation Protein Synthesis Biology 12 Genes and

Transcription & Translation Protein Synthesis Biology 12

Genes and Proteins l l Proteins become structures such as filaments in muscle tissue, and enzymes that control chemical reactions Sequences of nucleotides in DNA contain information that is used in the production of proteins

l l l Genes direct the production of proteins that determine the phenotypical characteristics of organisms. Genes also direct the production of other physiologically essential proteins such as antibodies and hormones. Proteins drive cellular processes such as metabolism; determining physical characteristics and producing genetic disorders by their absence or presence in an altered form.

The Central Dogma l l An organism’s genome is housed within the nucleus. Proteins are synthesized outside the nucleus, in the cytoplasm, on ribosomes. Since information for protein synthesis is specified by DNA (called the one gene-one polypeptide hypothesis), and DNA is not able to exist outside the nucleus, a problem exists as to how the blueprint of life is brought to the ribosomes.

SO…How does a cell make proteins anyway?

There are two important nucleic acids involved in this process. . . DNA RNA

Let’s Review DNA & RNA l l DNA: deoxyribonucleic acid--contains sugar deoxyribose. DNA is double stranded. DNA contains bases adenine, guanine, cytosine, and thymine. DNA never leaves the nucleus. l l RNA: ribonucleic acid-contains sugar ribose. RNA is single stranded. RNA contains bases adenine, guanine, cytosine and uracil. RNA can leave the nucleus. Ameoba Sisters- DNA vs RNA

There are three types of RNA l m. RNA: messenger RNA m. RNA zt. RNA: transfer RNA zr. RNA: ribosomal RNA Amin o ac id t. RNA towing

Types of RNA Genetic information copied from DNA is transferred to 3 types of RNA: Messenger RNA: m. RNA Copy of information in DNA that is brought to the ribosome and translated into protein by t. RNA & r. RNA Varies in length , the longer the gene the longer the m. RNA> Transfer RNA: t. RNA Brings the amino acid to the ribosome that m. RNA coded for. Ribosomal RNA: r. RNA Most of the RNA in cells is associated with structures known as ribosomes, the protein factories of the cells. Provides the construction site for the assembly of polypeptides. It is the site of translation where genetic information brought by m. RNA is translated into actual proteins. Transcription & Translation

Overall process of protein synthesis transcription DNA translation RNA Protein transcription translation Occurs in the nucleus Occurs in the cytoplasm Ameoba Sisters – Protein Synthesis

The Connection Between Genes and Proteins Hank again! Nucleic acids carry information in their nucleotide sequence. Proteins carry information in their amino acid sequence. To get from DNA (in nucleic acid language) to protein (in amino acid language) requires two steps. 1. Transcription- a DNA strand provides a template for the synthesis of a complementary RNA strand. This molecule is called m. RNA (messenger RNA). DNA is too valuable to be allowed to exit the nucleus. This could lead to the death of the cell and possible the Death of the organism.

- use of m. RNA provides protection for the Genetic information contained in DNA. - more protein can be made simultaneously because many m. RNA copies of a gene can be made than if one strand of DNA left the nucleus. - each m. RNA can be translated many times.

m. RNA delivers the encoded genetic material to the ribosomes. The ribosomes translate the message into polypeptide chains, which are processed into proteins. This entire sequence is described as the Central Dogma of Molecular Genetics, first stated by Francis Crick in 1958.

Central Dogma l In nucleus l l Produced in nucleus Travels to cytoplasm l Produced in cytoplasm

Transcription vs Translation Transcription involves the copying of the information in DNA into m. RNA. (copy from one medium to another- think of a medical or legal stenographer) Translation involves ribosomes using the Messenger RNA as a blueprint to synthesize a protein composed of amino acids. (converting into a different language, think English to French)

Transcription

Definition: Transcription Nucleus Location DNA Template (What is read) To change DNA into a form that can make a protein Purpose Messenger RNA (m. RNA) Outcome (End result)

Definition: Translation Location Cytoplasm (by ribosome) Template (What is read) m. RNA Purpose Amino acids assembled in particular order to make a protein Outcome (End result) Protein (polypeptide)

Transcription occurs in 3 steps: l l Initiation, Elongation and Termination Initiation: RNA polymerase binds to the DNA at a specific site known as a promotor. DNA: RNA: A T G C A A U A C G U U The RNA transcript is known as elongation. After the RNA polymerase passes the end of the gene, it stops transcribing which is termination.

Transcription : ‘to copy’ Initiation: l RNA polymerase binds to DNA at ‘promoter’ l untwists the double helix 10 to 20 bases at a time Elongation: l RNA polymerase builds m. RNA l l From DNA 3’ end Uses complimentary base pairing l Remember: thymine (T) is replaced by uracil (U)

Termination: l l l RNA polymerase reaches end of gene. Stops transcribing Double helix reforms as m. RNA molecule peels away. End Result: m. RNA breaks away from DNA l m. RNA exits nucleus l If there is a high demand for a protein, the cell can have several RNA polymerases transcribing the gene at the same time to produce several m. RNA’s. l

First, DNA unzips itself. . . l DNA unzips itself, exposing free nitrogen bases.

First, DNA unzips itself. . . l When DNA unzips itself (exposing free nitrogen bases)…

Next, m. RNA is made. . . m. RNA matches with free DNA nitrogen bases in a complementary fashion l (m. RNA is made from the DNA template) l

Next, m. RNA is made. . . l l m. RNA matches with free DNA nitrogen bases in a complementary fashion (m. RNA is made from the DNA template)

Next, m. RNA is made. . . m. RNA matches with free DNA nitrogen bases in a complementary fashion l (m. RNA is made from the DNA template) l

Translation: ‘new language’ Initiation: l Ribosome binds at a specific sequence on the m. RNA. l The ribosome moves along the m. RNA three nucleotides at a time. This is called a codon. Each set of three (a codon) codes for an amino acid. Why? There are only 4 bases but 20 amino acids. 41 = 4 (1 base=1 acid) 42 = 16 43 = 64 One code two codes three codes

The codon AUG not only codes for the amino acid Methionine, but it also indicates the start of a translation. Some amino acids are coded for by two or more codons but a given codon ALWAYS only codes for one amino acid. GAA and GAG both code for glutamic acid, but never mean any other amino acid.

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m. RNA tries to talk to the ribosomes… l m. RNA leaves the I have a message It’s nucleus and travels forfromyou!DNA! to the cytoplasm, where the ribosomes are located. Once there, m. RNA meets up with the ribosomes What does he want now? It’s always something!

m. RNA tries to talk to the ribosomes…but is unsuccessful. l However, the ribosomes cannot understand the message m. RNA is carrying. Why don’t they get it? ? ? @%$!! Why can’t we tell what he’s saying? We need a translator!

t. RNA Saves the Day! Methionine The boss will NOT be happy about this. . . We won’t work until we know what to do! Where is that translator? Looks like trouble for this cell… I’d better help! Now the cell can make a protein!

t. RNA: Transfer RNA Methionine l l l Chemically, t. RNA is clover-leaf shaped. At one end, it carries an amino acid. At the other end, it has a three letter code known as an anticodon.

Anticodon? What’s that? l l This anticodon is the complement to the codons contained within m. RNA. Can you find the m. RNA complement to the anticodon on t. RNA? Methionine

Elongation: Ribosome moves along m. RNA l From m. RNA 5’ end l 3 nucleotides of m. RNA = codon = amino acid l The “interpreter” t. RNA delivers the proper complimentary base to the ribosome. Anticodons are blocks of 3 t. DNA bases that actually attach to the correct protein. l The anticodon( t. RNA) binds by complimentary base pairing to the nucleotides of the codon. l Example: if the codon on a m. RNA is UUU, a t. RNA with an AAA anticodon will bind to it. The ribosome links adjacent amino acids with a peptide bond, causing the amino acid to let go of it t. RNA. The finished protein has a sequence of amino acids that have been determined by the m. RNA base sequence which has been translated by the t. RNA. l

The Whole Picture Next amino acid to be added to polypeptide Growing polypeptide t. RNA m. RNA

l l The ribosome then adds each amino acid and the polypeptide chain is elongated. Elongation occurs until a stop signal occurs. Termination: l Ribosome reaches stop codon l Stops translating End Result: l Ribosome falls off m. RNA l Protein (polypeptide chain) is released

Start and Stop Codons Start Codon: l Begins translation l AUG (universal start codon) l l ALSO Codes for methionine (Met) Sometimes GUG or UUG Stop Codon: l Ends translation l UGA, UAG

Third letter Codon Chart

Example l DNA template: 3’ TAC ACA CGG AAT GGG TAA ACT 5’ l Complimentary DNA l l m. RNA codon l l Read from DNA template (start reading at 3’) t. RNA anticodon l l Read from DNA template (start reading at 3’) Read from m. RNA Amino Acids (protein) l Read from m. RNA

Review. From DNA to Protein

RNA types l m. RNA l l Messenger RNA End product of transcription Takes message from DNA into cytoplasm Used by ribosome to make protein l t. RNA l l l Transfer RNA Delivers amino acid to ribosome r. RNA l l Ribosomal RNA Helps form and maintain ribosomes

Transcription/Translation Transcription l Purpose: l To make m. RNA from DNA l Location: l Nucleus Translation l Purpose: l To make a specific protein from m. RNA l Location: l Cytoplasm (ribosome)

Stop vs. Start Codon l m. RNA code l Tells ribosome to begin translation l Example: l AUG Also codes for methionine And: UUG, GUG l l Stop Codon l m. RNA code l Stops translation of that specific amino acid chain l Examples: l UAA, UAG, UGA

Transcribe to m. RNA l DNA: GGA TCA GGT CCA GGC AAT TTA GCA TGC CCC AA l *m. RNA*: CCU AGU CCA GGU CCG UUA AAU CGU ACG GGG UU

Translate to Amino Acids l m. RNA sequence divided into codons: GGC AUG GGA CAU UUU GCC CGU UGU GGG GCG UGA l *Protein translation*: Gly Met(start) Gly His Tyr Phe Ala Arg Cys Gly Ala (stop)

Transcribe to m. RNA l DNA: TAC GGT AGG TAT A l *m. RNA*: AUG CCA UCC AUA U

Change in 3 rd Base May Not Result in Error l Why not? l l Amino acids have more than one codon Example: proline l l l Codons CCU, CCC, CCA, and CCG CC - always codes for proline Third base/nucleotide does not matter