Presentation on theme: "Protein Synthesis The production (synthesis) of polypeptide chains (proteins) Two phases: Transcription & Translation mRNA must be processed before it."— Presentation transcript:
1 Protein SynthesisThe production (synthesis) of polypeptide chains (proteins)Two phases: Transcription & TranslationmRNA must be processed before it leaves the nucleus of eukaryotic cells
2 Pathway to Making a Protein DNAmRNAtRNA (ribosomes)Protein
3 RNA Differs from DNA DNA has a sugar deoxyribose 1. RNA has a sugar riboseDNA has a sugar deoxyribose2. RNA contains the base uracil (U)DNA has thymine (T)3. RNA molecule is single-strandedDNA is double-stranded
4 Structure of RNALike DNA, RNA is a polymer of nucleotides. In an RNA nucleotide, the sugar ribose is attached to a phosphate molecule and to a base, either G, U, A, or C. Notice that in RNA, the base uracil replaces thymine as one of the pyrimidine bases. RNA is single-stranded, whereas DNA is double-stranded.
6 Three Types of RNA.Messenger RNA (mRNA) carries genetic information to the ribosomesRibosomal RNA (rRNA), along with protein, makes up the ribosomesTransfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized
7 Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins. The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA.
8 Ribosomes are made up of proteins and ribosomal RNA (rRNA). The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Ribosomal RNA is combined with proteins to form ribosomes.Ribosomes are made up of proteins and ribosomal RNA (rRNA).
10 The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome.
11 Protein Synthesis DNA molecule DNA strand (template) 3¢ 5¢ TRANSCRIPTIONmRNA5¢3¢CodonTRANSLATIONProtein
12 Genes & ProteinsProteins are made of amino acids linked together by peptide bonds20 different amino acids existAmino acids chains are called polypeptidesSegment of DNA that codes for the amino acid sequence in a protein are called genes
13 Two Parts of Protein Synthesis Transcription makes an RNA molecule complementary to a portion of DNATranslation occurs when the sequence of bases of mRNA DIRECTS the sequence of amino acids in a polypeptide
14 Genetic Code Every three bases on DNA stands for ONE amino acid Each three-letter unit on mRNA is called a codonMost amino acids have more than one codon!The code is nearly universal among living organismsThe fact that the genetic code is about universal in living things suggests that the code dates back to the first organisms on earth and that all living things are related.
15 Notice that in this chart, each of the codons (white rectangles) is composed of three letters representing the first base, second base, and third base. For example, find the rectangle where C for the first base and A for the second base intersect. You will see that U, C, A, or G can be the third base. CAU and CAC are codons for histidine; CAA and CAG are codons for glutamine.
16 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
17 Overview of Transcription During transcription in the nucleus, a segment of DNA unwinds and unzips, and the DNA serves as a template for mRNA formationRNA polymerase joins the RNA nucleotides so that the codons in mRNA are complementary to the code in DNA
18 TranscriptionDNA is copied in the form of RNAThis first process is called transcription.The process begins at a section of DNA called a promoter.
19 RNA Polymerase Enzyme found in the nucleus Separates the two DNA strands by breaking the hydrogen bonds between the basesThen moves along one of the DNA strands and links RNA nucleotides together
20 RNADuring transcription, RNA polymerase uses one strand of DNA as a template to assemble nucleotides into a strand of RNA.
21 Messenger RNA (mRNA) Carries the information for a specific protein Made up of 500 to 1000 nucleotides longSequence of 3 bases called codonAUG – methionine or start codonUAA, UAG, or UGA – stop codons
22 A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid. A codon is a group of three nucleotides on messenger RNA that specify a particular amino acid.
23 Messenger RNA (mRNA) Primary structure of a protein A U G C mRNA start codoncodon 2codon 3codon 4codon 5codon 6codon 7codon 1methionineglycineserineisoleucinealaninestopcodonproteinPrimary structure of a proteinaa1aa2aa3aa4aa5aa6peptide bonds
24 Copyright Pearson Prentice Hall The Genetic CodeThe genetic code shows the amino acid to which each of the 64 possible codons corresponds. To decode a codon, start at the middle of the circle and move outward.Copyright Pearson Prentice Hall
25 Transfer RNA (tRNA)Picks up the appropriate amino acid floating in the cytoplasmTransports amino acids to the mRNAHave anticodons that are complementary to mRNA codonsRecognizes the appropriate codons on the mRNA and bonds to them with H-bonds
26 Translation Synthesis of proteins in the cytoplasm Involves the following:1. mRNA (codons)2. tRNA (anticodons)3. ribosomes4. amino acids
27 Copyright Pearson Prentice Hall TranslationTranslation is the decoding of an mRNA message into a polypeptide chain (protein).Translation takes place on ribosomes.During translation, the cell uses information from messenger RNA to produce proteins.NucleusmRNACopyright Pearson Prentice Hall
28 The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA. LysinePhenylalaninetRNAMethionineRibosomeDuring translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process.mRNAStart codon
29 Protein Synthesis Translation During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process.
30 The process continues until the ribosome reaches a stop codon. PolypeptideRibosomeDuring translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process.