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Protein Synthesis Human Biology
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DNA DNA Deoxyribonucleic Acid Twisted ladder or double helix
Nucleotides Composed of alternating sugar (Deoxyribose) and phosphate molecules and Nitrogen bases Purines = adenine and guanine Pyrimidines = thymine cytosine
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Fig. 25.3
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Fig. 25A
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DNA Purines bond with Pyrimidines Complementary base pairs Adenine with Thymine Guanine with Cytosine
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DNA Purines bond with Pyrimidines Nucleoside Nucleotide
Complementary base pairs Adenine with Thymine Guanine with Cytosine Nucleoside Sugar bonding with a base Nucleotide Adding a phosphate to a nucleoside Phosphates attach to the 5’ carbon of the sugar
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Orientation of DNA The carbon atoms on the sugar ring are numbered for reference. The 5’ and 3’ hydroxyl groups (highlighted on the left) are used to attach phosphate groups. The directionality of a DNA strand is due to the orientation of the phosphate-sugar backbone.
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DNA has directionality.
DNA is a double helix A sugar and phosphate “backbone” connects nucleotides in a chain. P T P A 3’ 5’ 5’ 3’ P C P G DNA has directionality. P C P G Two nucleotide chains together wind into a helix. P T P A Hydrogen bonds between paired bases hold the two DNA strands together. G P P C P C P G DNA strands are antiparallel.
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DNA 23 pair = diploid 23 = haploid; sex cells A chromosome
Duplicating DNA structure tightly packed around histone proteins to form a nucleosome.
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DNA and Genes
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DNA DNA contains genes Genes are the codes for polypeptides (proteins)
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DNA Gene Genetic Alphabet
A series of bases that occupy a specific location (locus) on a chromosome The code of a single protein or polypeptide Genetic Alphabet Triplet = Three nucleotides on DNA with their corresponding base pairs making up the code of a single amino acid Codon = Three successive nucleotides on RNA with their corresponding base pairs making up the code of a single amino acid 20 amino acids A series of amino acids makes up a protein
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DNA Consists of 3 billion base pairs
Codes for about 50 to 100,000 genes Genes may exist in alternate forms = alleles One allele from mom and one allele from dad Nucleotide changes or mutations may occur in a gene Sickle cell anemia In a healthy population, a gene may exist in multiple alleles Genetic Polymorphism = Multiple different forms at a gene locus in a population Basis for DNA typing using MHC
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Terminology Allele Locus Gene An alternate form of a gene
Location of a gene on a chromosome Gene Genetic code or “blueprint” for the cell to build one particular protein
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DNA DNA is located in the nucleus of the cell
Proteins are produced in the cytoplasm of the cell using ribosomes
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Protein Synthesis DNA is very large and must be copied in order to enter the cytosol The DNA code is read by the ribosome Amino acids are bonded to make proteins
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RNA
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DNA contains the Genetic Code
RNA is the BLUEPRINT or COPY of the Genetic Code
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RNA Differs from DNA RNA has a sugar ribose
DNA has a sugar deoxyribose
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Table 25.1
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Other Differences RNA contains the base uracil (U) DNA has thymine (T)
RNA molecule is single-stranded DNA is double-stranded DNA
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. 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
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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
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Ribosomal RNA (rRNA) rRNA is a single strand 100 to 3000 nucleotides long Globular in shape Made inside the nucleus of a cell Associates with proteins to form ribosomes Site of protein Synthesis
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Transfer RNA (tRNA) 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
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Transfer RNA amino acid attachment site U A C anticodon
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Codons and Anticodons The 3 bases of an anticodon are complementary to the 3 bases of a codon Example: Codon ACU Anticodon UGA
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Fig. 25.8
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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
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Pathway to Making a Protein
DNA mRNA tRNA (ribosomes) Protein
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Transcription and Translation
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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
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Transcription Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA Called the TATA box Specific base sequences act as signals to stop
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mRNA Processing 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 DNA are snipped out of the chain
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mRNA Editing Exons, segments of DNA that code for 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
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Fig. 25.7
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mRNA Transcript mRNA leaves the nucleus through its pores and goes to the ribosomes copyright cmassengale
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Translation Translation is the process of decoding the mRNA into a polypeptide chain Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins
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Transcription 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 copyright cmassengale
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Ribosomes Made of a large and small subunit
Composed of rRNA (40%) and proteins (60%) Have two sites for tRNA attachment --- P and A
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Step 1- Initiation mRNA transcript start codon AUG attaches to the small ribosomal subunit Small subunit attaches to large ribosomal subunit mRNA transcript
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Ribosomes Large subunit P Site A Site mRNA A U G C Small subunit copyright cmassengale
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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 copyright cmassengale
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Initiation 2-tRNA G aa2 A U 1-tRNA U A C aa1 anticodon A U G C U A C U U C G A hydrogen bonds codon mRNA copyright cmassengale
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Elongation 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 copyright cmassengale
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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
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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
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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
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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
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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
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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
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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
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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
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