Chapter 11

All living things are made of-  Water (an inorganic compound)  Other inorganic compounds (mostly salts)  Organic Compounds: contain carbon and hydrogen Carbohydrates Lipids(fats) Proteins Nucleic Acids

When we look at a living thing  What we see is mostly PROTEIN. How does an organism produce its particular protein?  As in, people protein vs tree protein?

The answer is DNA  The species-particular DNA sequences produce the species-particular proteins GENES code for proteins GENES are long strands of DNA on chromosomes

What is DNA?  DNA is the genetic code  Instructions for heredity  Components of genes  Director of protein synthesis

DNA is also  A type of nucleic acid  A type of organic compound  A polymer (a compound made of repeating subunits)

11.4 A gene provides the information for making a specific protein.  LT: Trace the information flow from DNA to protein.  LT: Describe how amino acids are coded.

Gene to Protein  Most genes control the production of a single polypeptide (which may make up part of an enzyme or other kind of protein). one gene – one polypeptide Through the process of protein synthesis

Gene to Protein DNA → RNA → Protein

How does DNA code for a protein?  What is “protein synthesis”? It’s building, or assembling, a protein molecule from amino acids Amino acids are smaller molecules found in the food we eat or produced in our cells It happens at the ribosomes

How does DNA code for protein?  Use of RNA Ribonucleic Acid (RNA) is a single strand nucleic acid, shape will vary ○ Uracil (instead of thymine) ○ Leaves the nucleus ○ Nucleotide: Ribose (sugar), phosphate, nitrogen base (4) The instructions for making proteins ○ RNA carries the messages from the DNA (in the nucleus) to the ribosomes (in the cytoplasm). RNA tells the ribosomes which proteins to make and how to make them. Made from DNA during transcription

Types of RNA  Messenger RNA (mRNA) Linear strand Carries the instructions from the DNA to the ribosomes in the cytoplasm Read in 3 letter (base) segments called codons Each codon translates into an amino acid or command ○ First Codon: Start ○ Last Codon: Stop

Types of RNA  Transfer RNA (t RNA) Twisted “hairpin” structure ○ Anticodon on one end ○ Amino Acid on other tRNA reads the message carried by mRNA and gathers the right amino acid for making that protein Transfers the amino acid to the site of protein synthesis – the ribosome ○ A cell keeps the cytoplasm stocked with all 20 amino acids

Types of RNA  Ribosomal RNA (rRNA) Makes up the ribosome Site of protein synthesis: mRNA brings the code here tRNA brings the amino acid here

11.5 There are two main steps from gene to protein.  LT: Describe the process of transcription.  LT: Explain how an RNA message is edited.  LT: Describe how RNA is translated to a protein.  LT: Summarize protein synthesis.

Steps in Protein Synthesis  Step A: Transcription (DNA making RNA)

Steps in Protein Synthesis  Step 1: DNA unzips (RNA helicase)  Step 2: mRNA nucleotide bond (RNA polymerase)  Step 3: mRNA is released, DNA twists back together Only certain portions (genes) are transcribed each time

Steps in Protein Synthesis  Remember: The purpose of transcription is NOT to copy the entire length of the DNA molecule, but to copy only small portions - a gene’s worth - to be sent to the ribosome as the: Instructions for protein synthesis.

Steps in Protein Synthesis  The RNA is not yet ready to be sent out to the cytoplasm. It must be modified before it is ready to serve its purpose.  The mRNA is a copy of a small section of DNA.  This RNA contains sections called introns and other sections called exons. Introns (non-coding) regions are removed from RNA Exons (remaining RNA) will be expressed. They will be joined together before leaving nucleus

Steps in Protein Synthesis  If introns are not needed and will be cut out of the RNA, why are they there in the first place? When introns are present in genes, it allows a single gene to code for more than one type of protein depending on which segments are treated at introns and which are treated as exons. When particular segments are cut out, one type of protein might result. If a different segment is cut out, a different protein would result.

Steps in Protein Synthesis  Step B: Translation (mRNA code being translated into polypeptides / proteins)

Steps in Protein Synthesis  mRNA brings message to the ribosome. The code is read 3 bases (1 codon) at a time.  tRNA molecules will bring specific amino acids to the ribosome. Each is checked (codon : anticodon).  The amino acid is released from tRNA and attaches to polypeptide chain.  Continues until a STOP command is read on mRNA

The Genetic Code  The genetic code is read three nitrogen bases at a time. Each group of three nitrogen bases is a codon.  Protein are made by joining together long chains of amino acids.  The order in which the amino acids are joined: determines the type of protein that is made.  The “language” of mRNA instructions is called the genetic code.

The Genetic Code  Consider the following mRNA sequence: UCGCACGGU  The sequence would be read three bases at a time UCG – CAC – GGU  There three codons represent three different amino acids. From your chart of amino acids, determine the three amino acid coded for by these codons Serine – Histidine – Glycine

The Genetic Code  Since there are four different nitrogen bases (A,T,C,G) read in groups of three, there are 64 possible codons.  There is one codon, AUG, which specifies methionine This codon serves as the “start” codon for protein synthesis. This codon is found at the beginning of every set of mRNA instruction.  There are three “stop” codons. These do not code for any amino acid. Stop codons act like the period at the end of the sentence. Stop codons signify the end of the protein.

If the sequence on the DNA molecule calls for a protein with the following DNA codons: (1) What would be the sequence of the mRNA? (2) What would be the sequence on the tRNA? (3) What would be the amino acid sequence of the protein being made? DNA  TAC TTA CAA ACC ATA ATT mRNA  tRNA  AUGAAUGUUUGGUAUUAA CODONS ANTICODONS UACUUACAAACCAUAAUU MethionineAsparagine ValineTryptophan Tyrosine STOP Amino  Acid Sequence

If the sequence on the DNA molecule calls for a protein with the following DNA codons: (1) What would be the sequence of the mRNA? (2) What would be the sequence on the tRNA? (3) What would be the amino acid sequence of the protein being made? DNA  TAC TTA CAA ACC ATA ATT mRNA  tRNA  CODONS ANTICODONS Amino  Acid Sequence

The Genetic Code  The codons MUST be read correctly and in the correct order. Consider this… THE RED DOG ATE THE CAT  If the reading of the code starts at the wrong place by omitting the first “T” HER EDD OGA TET HEC AT  The result will be gibberish. A protein will be made putting the wrong amino acids in order. It is unlikely that this protein will be able to function.