PROTEIN SYNTHESIS Chapter 9 Bio 2A

What are some examples of proteins?

Why are Proteins Important? Structural Proteins Keratin = skin and Myosin = muscle Enzymes – speed up reactions Hemoglobin-transports oxygen on RBC’s Hormones – Insulin keeps blood sugar in check Receptor proteins-allow things to enter and leave cells

Keratin

Myosin

Insulin Hormone

Enzymes

Receptor Proteins

DNA DNA contains genes, sequences of nucleotide bases These Genes code for polypeptides (proteins) Proteins are used to build cells and do much of the work inside cells

Genes & Proteins Proteins are made of amino acids linked together by peptide bonds 20 different amino acids exist

Polypeptides Amino acid chains are called proteins or polypeptides…all the same thing.

DNA Begins the Process DNA is found inside the nucleus Proteins are made in the cytoplasm of cells at organelles called ribosomes Ribosomes may be free in the cytoplasm or attached to the surface of rough ER

Why can’t DNA leave the nucleus? Degradation, damage, distortion Inefficient protein production…each protein would have to be made one at a time since there is only one DNA molecule. It would have to have a nucleus reentry strategy

Starting with DNA DNA ‘s code must be copied and taken to the cytoplasm In the cytoplasm, this code must be read so amino acids can be assembled in the right order to make certain polypeptides (proteins) This process is called PROTEIN SYNTHESIS

The Central Dogma of molecular genetics Genes found within a DNA sequence are transcribed into messenger RNA. Messenger RNA exits the nucleus and is translated into protein by ribosomes in the cytoplasm

DNA  mRNA  Protein Eukaryotic Cell DNA Pre-mRNA mRNA Ribosome Nuclear membrane Transcription RNA Processing Translation DNA Pre-mRNA mRNA Ribosome Protein Eukaryotic Cell

RNA and DNA RNA has a sugar ribose DNA has a sugar deoxyribose

RNA and DNA RNA contains the base uracil (U) DNA has thymine (T) RNA molecule is single-stranded DNA is double-stranded RNA DNA

Structure of RNA

Three Types of RNA . Messenger RNA (mRNA) –copies DNA’s code & carries the genetic information to the ribosomes Ribosomal RNA (rRNA) -along with protein, makes up the ribosomes Transfer RNA (tRNA) -transfers amino acids to the ribosomes where proteins are synthesized

Messenger RNA Long Straight chain of Nucleotides Made in the Nucleus Contains the Nitrogen Bases A, G, C, U ( no T ) Copies DNA & leaves through nuclear pores

Messenger RNA (mRNA) Ribosomes make proteins using mRNA as the template. Ribosomes read mRNA in a sequence of 3 bases at a time. This 3 base sequence is called a codon AUG – methionine or start codon UAA, UAG, or UGA – stop codons

Ribosomal RNA (rRNA) – RIBOSOMES Made inside the nucleus of a cell It’s made of rRNA and protein. Can adhere to RER or float freely in cytoplasm Site of protein synthesis

The Genetic Code Each codon (three base sequence on mRNA) codes for a specific amino acid. Scientists hae figured out which codon codes for which amino acid Example: AUG codes for Methionine

Practice GGG? UCA? CAU? GCA? AAA?

Transfer RNA (tRNA) Clover-leaf shape amino acid attachment site U A C anticodon Clover-leaf shape Single stranded molecule with attachment site at one end for an amino acid Opposite end has three nucleotide bases called the anticodon

Codons and Anticodons The 3 bases of an anticodon are complementary to the 3 bases of a codon Example: Codon ACU Anticodon UGA UGA ACU

Some Characteristics of Protein Synthesis All RNA is built in the Nucleus mRNA is assembled from DNA in the nucleus rRNA and tRNA travel and work outside of the nucleus rRNA + protein = Ribosomes tRNA = has the anticodon at one end and the proper amino acid at the other mRNA travels out of nucleus to a ribosome to start making proteins

Step 1 - Transcription The process of copying the sequence of one strand of DNA, the template strand mRNA copies the template strand Requires the enzyme RNA Polymerase

What would be the complementary RNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’

RNA Polymerase

http://vcell. ndsu. nodak. edu/animations/transcription/movie-flash http://vcell.ndsu.nodak.edu/animations/transcription/movie-flash.htm

Transcription During transcription, RNA polymerase binds to DNA and separates the DNA strands RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA Regions promoters start is called the TATA box Specific base sequences act as signals to stop Called the termination signal

Result of Transcription New Transcript Tail CAP

mRNA Processing & Editing After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional Introns, non-functional segments of RNA are snipped out of the chain Exons, segments of RNA that are expressed into proteins, are then rejoined by the enzyme ligase A guanine triphosphate cap is added to the 5” end of the newly copied mRNA A poly A tail is added to the 3’ end of the RNA The newly processed mRNA can then leave the nucleus

mRNA Transcript mRNA leaves the nucleus through its pores and goes to the ribosomes

Messenger RNA (mRNA) Primary structure of a protein A U G C aa1 aa2 start codon codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 codon 1 methionine glycine serine isoleucine alanine stop codon protein Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds 40 40

Translation Translation is the process of decoding the mRNA into a protein Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins http://vcell.ndsu.nodak.edu/animations/translation/movie-flash.htm

Transcription Translation Transcription occurs when DNA acts as a template for mRNA synthesis. Translation occurs when the sequence of the mRNA codons determines the sequence of amino acids in a protein. Translation

Ribosomes Made of a large and small subunits Composed of rRNA (40%) and proteins (60%) Have two sites for tRNA attachment --- P and A P= where peptide bond is made A= where new amino acid is delivered by the tRNA

Ribosomes Large subunit P Site A Site mRNA A U G C Small subunit

Step 1- Initiation mRNA transcript start codon AUG attaches to the small ribosomal subunit large subunit attaches to the small ribosomal subunit mRNA transcript

Step 2 - Elongation As ribosome moves, two tRNA with their amino acids move into site A and P of the ribosome Peptide bonds join the amino acids

Initiation G aa2 A U U A C aa1 A U G C U A C U U C G A codon 2-tRNA anticodon A U G C U A C U U C G A hydrogen bonds codon mRNA

Elongation G A aa3 peptide bond aa1 aa2 U A C G A U A U G C U A C U U 3-tRNA G A aa3 peptide bond aa1 aa2 1-tRNA 2-tRNA anticodon U A C G A U A U G C U A C U U C G A hydrogen bonds codon mRNA

Ribosomes move over one codon aa1 peptide bond 3-tRNA G A aa3 aa2 1-tRNA U A C (leaves) 2-tRNA G A U A U G C U A C U U C G A mRNA Ribosomes move over one codon

peptide bonds G C U aa4 aa1 aa2 aa3 G A U G A A A U G C U A C U U C G 4-tRNA G C U aa4 aa1 aa2 aa3 2-tRNA 3-tRNA G A U G A A A U G C U A C U U C G A A C U mRNA

Ribosomes move over one codon peptide bonds 4-tRNA G C U aa4 aa1 aa2 aa3 2-tRNA G A U (leaves) 3-tRNA G A A A U G C U A C U U C G A A C U mRNA Ribosomes move over one codon

peptide bonds U G A aa5 aa1 aa2 aa4 aa3 G A A G C U G C U A C U U C G 5-tRNA aa5 aa1 aa2 aa4 aa3 3-tRNA 4-tRNA G A A G C U G C U A C U U C G A A C U mRNA

Ribosomes move over one codon peptide bonds U G A 5-tRNA aa5 aa1 aa2 aa3 aa4 3-tRNA G A A 4-tRNA G C U G C U A C U U C G A A C U mRNA Ribosomes move over one codon

Termination aa5 aa4 aa3 primary structure of a protein aa2 aa1 A C U C terminator or stop codon 200-tRNA A C U C A U G U U U A G mRNA

Step 3- Termination Once the ribosome reaches the stop codon on the mRNA, the protein is complete. The protein detaches, is modified and will be transported to where it works in the cell.

End Product –The Protein! The end products of protein synthesis is a primary structure of a protein A sequence of amino acid bonded together by peptide bonds aa1 aa2 aa3 aa4 aa5 aa200 aa199

Transport & Modification of Proteins Protein must be modified –folded Ex: Pepsin and Trypsin Protein must be transported to where it will function. Ex: outside of cell if hormone, to cell membrane if receptor, etc. Faulty proteins (with errors) are broken down by proteosomes Normal proteins will also be destroyed Normal proteins have a life span Ex: protein with Phe at end only survive a few minutes

Translation Errors If the whole reading frame is shifted by a few nucleotides – Frameshift mutations Ex: Insertion – nucleotide has been inserted on mRNA strand Ex: Deletion – nucleotide has been deleted from mRNA strand

Point Mutations Involve the change in ONE nucleotide Example: Substitution – when one base is substituted for another. May or may not affect protein.

Viruses Not made of cells, but replicate and divide Consist of a Protein coat & a little genetic material Contain DNA as genetic material or some contain RNA as genetic material Some contain enzymes Some contain membrane envelope – still not made of cells Ex: Bacteriophage, HIV, Influenza

Viral Replication Same as for cells Two Patterns: 1. Lytic – the host (organism the virus is infecting) cells’ enzymes replicate the viral DNA. New viruses are made and the cell breaks open & releases them to infect new cells 2. Lysogenic- The Viral DNA inserts into cellular DNA & is copied when the cell replicates. Few or no new viruses are made unless a lytic cycle of replication occurs.

Impact of Viruses Live at the expense of the host Replicate & evolve quickly Can lie hidden or dormant Viruses do not metabolize-antibiotics are useless against them. Viruses can infect animals and plants Reverse transcriptase- a viral enzyme that makes a DNA copy of the viral RNA. The viral DNA then directs production of new virus particles (HIV) by incorporating itself into the hosts DNA.

Retrovirus…like HIV Retroviruses - employ the enzyme reverse transcriptase to produce DNA from the viral RNA. The newly produced DNA enters the nucleus and begins the process of viral replication