Protein Synthesis The production (synthesis) of polypeptide chains (proteins) Two phases: Transcription & Translation mRNA must be processed before it leaves the nucleus of eukaryotic cells

Pathway to Making a Protein DNA mRNA tRNA (ribosomes) Protein

RNA Differs from DNA DNA has a sugar deoxyribose 1. RNA has a sugar ribose DNA has a sugar deoxyribose 2. RNA contains the base uracil (U) DNA has thymine (T) 3. RNA molecule is single-stranded DNA is double-stranded

Structure of RNA Like 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.

Three Types of RNA . Messenger RNA (mRNA) carries 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 (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.

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).

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.

Protein Synthesis DNA molecule DNA strand (template) 3¢ 5¢ TRANSCRIPTION mRNA 5¢ 3¢ Codon TRANSLATION Protein

Genes & Proteins Proteins are made of amino acids linked together by peptide bonds 20 different amino acids exist Amino acids chains are called polypeptides Segment of DNA that codes for the amino acid sequence in a protein are called genes

Two Parts of Protein Synthesis Transcription makes an RNA molecule complementary to a portion of DNA Translation occurs when the sequence of bases of mRNA DIRECTS the sequence of amino acids in a polypeptide

Genetic Code Every three bases on DNA stands for ONE amino acid Each three-letter unit on mRNA is called a codon Most amino acids have more than one codon! The code is nearly universal among living organisms The 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.

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.

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

Overview of Transcription During transcription in the nucleus, a segment of DNA unwinds and unzips, and the DNA serves as a template for mRNA formation RNA polymerase joins the RNA nucleotides so that the codons in mRNA are complementary to the code in DNA

Transcription DNA is copied in the form of RNA This first process is called transcription. The process begins at a section of DNA called a promoter.

RNA Polymerase Enzyme found in the nucleus Separates the two DNA strands by breaking the hydrogen bonds between the bases Then moves along one of the DNA strands and links RNA nucleotides together

RNA During transcription, RNA polymerase uses one strand of DNA as a template to assemble nucleotides into a strand of RNA.

Messenger RNA (mRNA) Carries the information for a specific protein Made up of 500 to 1000 nucleotides long Sequence of 3 bases called codon AUG – methionine or start codon UAA, UAG, or UGA – stop codons

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.

Messenger RNA (mRNA) Primary structure of a protein A U G C mRNA 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

Copyright Pearson Prentice Hall The Genetic Code The 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

Transfer RNA (tRNA) Picks up the appropriate amino acid floating in the cytoplasm Transports amino acids to the mRNA Have anticodons that are complementary to mRNA codons Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds

Translation Synthesis of proteins in the cytoplasm Involves the following: 1. mRNA (codons) 2. tRNA (anticodons) 3. ribosomes 4. amino acids

Copyright Pearson Prentice Hall Translation Translation 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. Nucleus mRNA Copyright Pearson Prentice Hall

The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA. Lysine Phenylalanine tRNA Methionine Ribosome 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. mRNA Start codon

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.

The process continues until the ribosome reaches a stop codon. Polypeptide Ribosome 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.

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