Protein Synthesis

Protein Synthesis

RNA Structure and Function • The double helix structure of DNA explains how DNA is stored • The next few days we will talk about how the information in DNA will become an expressed gene • This process of information to expression is what gives organisms their traits

RNA Structure and Function • The first step in decoding the information in genes is to copy a DNA sequence to RNA • RNA molecules carry out the process of making proteins

RNA Structure and Function • RNA has a structure that is similar to the structure of DNA • RNA – Ribonucleic acid • The RNA nucleotide is similar to DNA but does not exclude an oxygen on the second carbon

RNA Structure and Function • Another key difference is that RNA is single stranded • It forms a single helix instead of a double helix • This means that all of RNA’s bases are unpaired when RNA is by itself

RNA Structure and Function • A third major difference is the base pairing rules that are true for RNA • RNA substitutes the nitrogen base uracil for thymine • Uracil is a nitrogen base that falls into the pyrimidine family

RNA Structure and Function • JUST TO REVIEW! • RNA forms nucleotides that are slightly different from DNA • RNA is a single helix • RNA substitutes Uracil for Thymine

Types of RNA • There are three main types of RNA • mRNA • tRNA • rRNA • They each have a different and specific function when it comes to making proteins • Many of these types of RNA will be edited and changed throughout their lifetime • DNA is not edited or changed

Types of RNA • Messenger RNA or mRNA carries copies of the DNA • mRNA is the messenger between the DNA (recipe) and the ribosomes (kitchen) • It starts in the nucleus but leaves to go to the ribosomes • If RNA is damaged or changed, we can always make more

Types of RNA • Ribosomes are made of two different subunits that fix together • Each subunit is made up of many proteins and ribosomal RNA or rRNA • This makes the ribosome the perfect place for translation

Types of RNA • Transfer RNA or tRNA is molecule that carries amino acids to where they are assembled into proteins • They also have a RNA codon that allows them to figure out where to go • This codon is a three nucleotide base sequence that allows the tRNA to know where to drop off its amino acid

Protein Synthesis • We have learned that DNA holds the information needed to turn genotypes into phenotypes • Now we need to learn the process of going from “A”s, “G”s, “C”s and “T”s into physical things that can be seen

Protein Synthesis • Protein synthesis is the process of going from a section of DNA to a protein • DNA codes for different proteins that can be used by the body to perform cellular processes

Protein Synthesis • Protein synthesis is made up of two different processes • Transcription is the process of going from DNA to mRNA • Translation is the process of going from mRNA to a fully formed protein

Transcription Begins • Transcription is happening at all times on DNA • It starts at an area of the DNA called a promoter • A promoter is a section of DNA that allows enzymes to attach and begin transcription

Transcription Begins • At the promoter an enzyme called RNA Polymerase attaches and begins to perform transcription • RNA polymerase is an enzyme with three main functions • Binds to DNA • Separates DNA strands • Creates complementary RNA strand

The Process • Once RNA polymerase attaches to DNA it unzips a small section of DNA and creates a small section of RNA • The RNA is created by creating a complementary strand of RNA from the unzipped DNA • This is similar to DNA replication, however we are making RNA

The Process • This continues until RNA polymerase hits a terminator • A terminator is a section of DNA that lets the RNA polymerase know when to stop transcribing

The Process • The resulting polymer is not quite mRNA yet • This RNA is almost ready to leave the nucleus and begin translation • Before it can leave the nucleus it has to be edited for the benefit of the cell

Video • http://www.youtube.com/watch?v=ztPkv7wc3yUhttp://www.youtube.com/watch?v=5MfSYnItYvg

mRNA Editing • Once the RNA is done being copied it has to be edited • This allows the cell to cut out sections that are not needed and keep sections that are important • This process is called RNA splicing

mRNA Editing • When it edits RNA the sections that are kept are called exons (expressed sequences) and the sections that are thrown out are called introns (intervening sequences) • This gives RNA the ability to be changed

mRNA Editing • The resulting polymer made from exons is “capped” and is called mRNA • This mRNA is free to leave the nucleus and begin translation

Translation • The process of taking a completed mRNA information and creating proteins is called translation • This is because you are translating the message of RNA to a sequence of amino acids • Translation has three main phases • Initiation • Elongation • Termination

Translation • The process of translation happens in a ribosome • In the ribosome the mRNA brings instructions in the form of nucleotides • tRNA brings amino acids and drops them off in specific locations

Translation • During translation mRNA is “read” in codons • Codons are sections of three nucleotides that are in mRNA • Codons allow tRNA to know where to drop off their amino acid

Initiation • Initiation begins when a strip of mRNA reaches a ribosome • The mRNA binds to the small subunit of a ribosome • The specific orientation of the mRNA and rRNA allows the rest of the steps to happen

Initiation • mRNA begins to be “read” at the start codon • This is a very specific set of three nucleotides that will allow more amino acids to be attached after the start codon • They always code for the amino acid methionine

Elongation • The process of elongation happens after initiation • Elongation is when amino acids are fixed together by the ribosome and a long string of amino acids (a polypeptide) is created • In elongation amino acids are added to the existing methionine

Elongation • The amino acids are formed however, they have to be formed very specifically • This is why the ribosome has two different sites for the creating of polypeptides • The P site will hold the growing polypeptide • The A site will is used to hold the next tRNA that is going to drop off an amino acid

Elongation • During elongation a tRNA with an amino acid is brought to the A site while the T site is filled • A peptide bond is formed between the amino acids • Then the T site is vacated and the tRNA from the A site is transferred to the T site

Termination • This process continues until there is a stop codon that stops elongation • Like there is only one start codon, there is only three stop codons • The stop codon does not actually code for an amino acid

Termination • After the stop codon the tRNA is released into the cytoplasm • The ribosome is now free to get a new piece of mRNA and start all over again

Video • http://www.youtube.com/watch?v=5bLEDd-PSTQ-PSTQ

Protein Synthesis