NOTE SHEET 13 – Protein Synthesis

What are the “instructions” that are found in DNA? DNA holds the instructions to build proteins Proteins are important because they make up many of the structures in an organism and perform many functions Human DNA holds the instructions to build about 30,000 different proteins!

Proteins Determine Traits It is the presence of specific proteins that give an organism its characteristics and allow it to function The instructions to build these specific proteins are in the organism’s DNA

Why are you a human? The DNA in all your cells holds the instructions to make the specific proteins necessary to form the structures of and perform the functions of a human organism

How are proteins built by a cell? Cells build proteins out of small molecules called amino acids – the amino acids are bonded together making a long protein chain Proteins are built at the ribosomes DNA instructions tell the cell which amino acids to use and where to put them in the chain Protein Synthesis – the process where cells build protein using instructions stored in DNA

What is RNA? RNA (ribonucleic acid) – a long, single-stranded molecule made out of nucleotides that helps cells build protein RNA has ribose sugar, and the bases A, C, G, and U (uracil)

DNA vs RNA DNA is a double helix, RNA is a single strand DNA has deoxyribose sugar in its nucleotides, RNA has ribose sugar in its nucleotides RNA has the nitrogen base uracil (U) instead of thymine (T)

There are 3 types of RNA: messenger (mRNA) – carries a copy of DNA instructions from the nucleus to the ribosome transfer (tRNA) – brings amino acids to the ribosome and puts them in the correct order ribosomal (rRNA) – bonds the amino acids together to make a protein chain

Building a protein is like building a house… You need a blueprint (instructions) for the house in the construction office – this is like the DNA in the nucleus You need a work site to build the house – this is like the ribosome You need a copy of the blueprint that can travel to the work site – this is like the mRNA You need workers to deliver the materials to build the house to the job site – this is like the tRNA You need builders to put all the materials together and make the house – this is like the rRNA

Building a protein is like building a house… The blueprint is copied and the copy is brought to the work site. Workers bring the correct materials to the work site and set them up according to the information in the blueprint. Builders put everything together building the house. An mRNA copy is made of DNA and the mRNA travels to the ribosome. The tRNA brings the correct amino acids to the ribosome and lines them up according to the information in the mRNA. The rRNA puts the amino acids together forming the protein.

What are the 2 steps of protein synthesis? Transcription – process where DNA instructions are copied in the nucleus DNA unzips and a mRNA copy is made Transcription takes place in the nucleus The mRNA leaves the nucleus and travels to the ribosome

What are the 2 steps of protein synthesis? Translation – process where a protein is built at the ribosome tRNA “reads” the instructions in the mRNA, brings the correct amino acids to the ribosome and lines them up in the correct order rRNA bonds the amino acids together making a protein chain Translation takes place at the ribosome

DNA unzips

An mRNA copy is made of DNA

An mRNA copy is made of DNA

An mRNA copy is made of DNA

An mRNA copy is made of DNA

An mRNA copy is made of DNA

An mRNA copy is made of DNA

An mRNA copy is made of DNA

An mRNA copy is made of DNA

An mRNA copy is made of DNA

An mRNA copy is made of DNA

The mRNA leaves the nucleus and travels to the ribosome

tRNA “reads” the instructions in the mRNA, brings the correct amino acids to the ribosome and lines them up in the correct order

tRNA “reads” the instructions in the mRNA, brings the correct amino acids to the ribosome and lines them up in the correct order

rRNA bonds the amino acids together making a protein chain

rRNA bonds the amino acids together making a protein chain

A protein is a chain of amino acids just like a word is a chain of letters There are 20 amino acids and there are 26 letters in the English alphabet In order to spell a word you need to know which letters to use and what order to put them in, and likewise, to build a protein a cell needs to know which amino acids to use and what order to put them in

If you need to know how to spell a specific word, a dictionary will tell you what letters to use and what order to put them in If a cell needs to build a specific protein, DNA will “tell” the cell what amino acids to use and what order to put them in

The Genetic Code Every 3 bases on an mRNA molecule stands for aan amino acid These pieces of mRNA are called codons Each codon in the mRNA tells a cell which of the 20 amino acids to use

How To Transcribe DNA bases: A T C G Bond with mRNA bases: U A G C

How To Transcribe – Example 1 DNA: TAC TCA CGC ATC mRNA: AUG AGU GCG UAG

How to Translate Every 3 mRNA bases together stand for 1 amino acid in the protein chain – these pieces of mRNA are called codons Use the amino acid chart to figure out which amino acid each codon stands for

How to Translate – Example 1 mRNA: AUG AGU GCG UAG AUG = Met (start codon) AGU = Ser GCG = Ala UAG = STOP Protein: Met-Ser-Ala-STOP

Transcribe and Translate –Example 2 DNA : TAC TGA ATA CCT CAA GGA GGC ACC TGG ACT mRNA: AUG ACU UAU GGA GUU CCU CCG UGG ACC UGA Protein: Met-Thr-Tyr-Gly-Val-Pro-Pro-Trp-Thr-Stop

Transcribe and Translate –Example 3 DNA : TAC AAA GGA CGA GTA GTT TAA GCA AGA ATT mRNA: AUG UUU CCU GCU CAU CAA AUU CGU UCU UAA Protein: Met-Phe-Pro-Ala-His-Glu-Ile-Arg-Ser-Stop

Mutation Mutation – Any change in the DNA base sequence which leads to a change in a protein. Sometimes mutation are beneficial, but they usually lead to non-functioning or incorrectly functioning proteins.

Point Mutation – One base in sequence is changed Original DNA: TAC AAA GGA CGA GTA GTT TAA GCA AGA ATT Original Protein: Met-Phe-Pro-Ala-His-Glu-Ile-Arg-Ser-Stop 4th triplet in DNA, first base C changed to G Mutated DNA: TAC AAA GGA GGA GTA GTT TAA GCA AGA ATT Incorrect mRNA: AUG UUU CCU CCU CAU CAA AUU CGU UCU UAA Mutated Protein: Met-Phe-Pro-Pro-His-Glu-Ile-Arg-Ser-Stop The 4th amino acid is proline instead of alanine

Point Mutation

Frameshift Mutation – One base added or deleted from the DNA sequence Original DNA: TAC AAA GGA CGA GTA GTT TAA GCA AGA ATT Original Protein: Met-Phe-Pro-Ala-His-Glu-Ile-Arg-Ser-Stop 2nd triplet in DNA, first base A deleted Mutated DNA: TAC AAG GAC GAG TAG TTT AAG CAA GAA TT Incorrect mRNA: AUG UUC CUG CUC AUC AAA UUC GUU CUU AA Mutated Protein: Met-Phe-Leu-Leu-Ile-Lys-Phe-Val-Leu After the second amino acid, the protein is completely different

Frameshift Mutation

Why is it important to eat protein? Your body needs 20 different amino acids to make all the necessary proteins Your body is only able to produce 12 of these amino acids on its own The other 8 amino acids come from foods you eat that contain protein (meat, nuts, dairy products, beans, etc.) – These are called essential amino acids because you cannot survive without eating them

The bottom line about DNA… No DNA = No Protein = No Cells = No Life Reproduction is all about passing DNA from one cell to another and from one generation of organisms to the next