Protein Synthesis: Transcription

Objectives What is the Central Dogma of biology? What are the steps of transcription?

Recall Why do we need proteins? Muscles, hair, nails cartilage, tendons, ligaments Enzymes Hemoglobin Antibodies

Central Dogma How genetic information flows in a system. Must convert the code to RNA and then to a Protein What does dogma mean ? established opinion, believed to be true. Code of beliefs So how do we make proteins that are so essential ??

What are proteins made of? Amino Acids are the individual building blocks Together to make one Protein There are 20 types of amino acids, some There are infinite combinations of amino acids These long chains are called polypeptide chains Amino acids are monomers, that make up the polymer, protein Polypeptide, because the bond holding amino acids together are peptide bonds

Protein Synthesis Protein synthesis is the process in which a cell makes protein based on the message contained within its DNA. However: DNA is only found in the nucleus Proteins are only made outside the nucleus – in the cytoplasm.

Protein Synthesis How do the many different messages within the DNA molecule get to the many ribosomes outside the nucleus? A molecular cousin of DNA – RNA – is used to carry these messages.

Ribonucleic Acids - RNA The job of RNA (ribonucleic acid) is to carry messages from the DNA (in the nucleus) to the ribosomes (in the cytoplasm).

Differences between RNA and DNA Single Stranded Ribose sugar group Nitrogen Base Pairs A-U, C-G DNA Double-stranded Deoxyribose sugar group Nitrogen Base Pairs A-T, C-G Nucleotides are made up of Phosphate group sugar Nitrogen bases DNA vs RNA Deoxyribonucleic acid and RiboNucleic acid hydroxy group on RNA and not DNA – extra O does not allow to form a double helix

Types of RNA mRNA: carries the message from the DNA to the cytoplasm tRNA: transports amino acids to the mRNA to make the protein rRNA: make up the ribosomes, which help make the protein mRNA – carries code into cytoplasm where translation will occur tRNA – reads the code and carries the amino acid to be in protein rRNA- found on the RNA itself. Helps make the peptide

Protein Synthesis Process Occurs in TWO steps: Transcription – the genetic information from a strand of DNA is copied into a strand of mRNA Translation

Steps of Transcription 1. DNA unwinds Enzymes help split apart base pairs to open the DNA double helix. Transcription complex: RNA polymerase and proteins Uses one strand as a template 2. Bases line up Free nucleotides in the cell find their complementary base pairs on the DNA template strand What will be different??

Steps of Transcription 3. RNA formed The growing RNA strand hands greely as it is transcribed. DNA strand must close back up 4. The completed RNA strand separates from the DNA template

Steps of Transcription http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

Try It! What will the RNA Strand be? TACGCATGGCATGCAA

Try It! What will the RNA Strand be? TACGCATGGCATGCA AUGCGUACCGUACGU

Think, Pair, Share 1. What is the purpose of Protein Synthesis? 2. List 2 differences between DNA and RNA 3. Where in the cell does the process of transcription occur? 4. What enzyme completes the process of transcription? 5. What molecule is produced from transcription? 6. Where does this molecule go after it is made?

Introns and Exons The DNA that is copied contains both… Introns: sequences of nucleotides not involved in coding for proteins. AND Exons: DNA sequences that code for proteins

By the end of the day today you should: Objectives By the end of the day today you should: Know the steps of translation Identify the differences in transcription and translation

Translation Now that the mRNA has been made, the next step is for its’ message to be made into a protein Translation: the mRNA, with the help of the ribosome, forms a chain of amino acids (eventually forming a protein) based on the information contained on the mRNA. Occurs in the cytoplasm on the ribosome

Proteins Proteins are made of amino acids 20 different amino acids total Adult humans can only make 12 out of the 24 amino acids How do we attain the other 8 amino acids? Some amino acids can be converted to each other, but not created from scratch. Some amino acids can be synthesized, but not rapidly enough to meet all our metabolic needs. And children can’t synthesize some of the amino acids that adults can.

Translation One Problem There are 20 amino acids There are 4 RNA bases How can just four nucleotides—A, U, C, G—be translated into so many different amino acids?

Language of RNA Just like the alphabet, 26 letters can make more than 26 words Letters of RNA are put together in different ways. Codon: three nucleotide sequence which codes for the insertion of a unique amino acid Language of the genetic code Multiple codons for the same amino acid Anticodon: on one end of tRNA complementary to a specific mRNA codon tRNA molecules carry different amino acids

Genetic Code Start Codon – signals the start of translation (AUG- Methionine) Stop codon – signal the end of the amino acid chain (3 total)

Translation Before translation begins, a ribosome will be assembled from two ribosomal subunits (large and small). The ribosome contains three attachment sites for tRNA molecules. On the large subunit: E site, A site and P site On the small subunit: mRNA joins

Step 1: mRNA attaches to the small ribosomal unit Step 1: mRNA attaches to the small ribosomal unit. The large subunit attaches to the small subunit. The first codon is aligned at the P site.

Step 2: A tRNA carrying the amino acid methionine attaches to the start codon, AUG, on the mRNA. This happens at the P site on the large ribosome

Step 3: Attachment of the first amino acid carrying tRNA to A binding site.

Step 4: The ribosome forms a peptide bond between the two amino acids and breaks the bond between the first tRNA and its amino acid.

Step 5: The ribosome pulls the mRNA the length of one codon Step 5: The ribosome pulls the mRNA the length of one codon. The tRNA and polypeptide chain move to the P site. The first tRNA is shifted to the E site.

Step 6: tRNA is ejected from the E binding site and returns to the cytoplasm. The A site is now open for another tRNA.

Step 7: This process continues to translate the mRNA strand until it reaches a stop codon. The protein is released and the large and small ribosome disassemble.

st. olaf transcription animation whfreeman animation http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

Mutations

Objectives What are different types of mutations that can occur during protein synthesis?

Mutations Mutations are changes in the DNA sequence DNA damage from environmental agents: UV Light Chemicals Mistakes that occur when DNA is copied before cell division Point Mutation: a change in a single base pair of a gene

No Mutation: DNA Sequence: TACAAG mRNA Sequence: AUGUUC Amino Acid Chain: Met – Phen Point Mutation: DNA Sequence: TACATG mRNA Sequence: AUGUAC Amino Acid Chain: Met – Tyr

Other Types of Mutations Substitution change a codon to one that encodes the same amino acid and causes no change in the protein produced. change a codon to one that encodes a different amino acid and cause a small change in the protein produced

Other Types of Mutations Insertions mutations in which extra base pairs are inserted into a new place in the DNA

Other Types of Mutations Deletion mutations in which a section of DNA is lost, or deleted.