Bs Nursing Level 1 Biochemistry Lecture (MC 2 Lec) - Nucleic Acid PDF

BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ 5-carbon sugar is either ribose or OUTLINE...

BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ 5-carbon sugar is either ribose or OUTLINE deoxyribose making the nucleotide either a ribonucleotide or a 1.1 INTRODUCTION TO NUCLEIC ACID deoxyribonucleotide. 1.2 NUCLEOTIDE STRUCTURE In eukaryotic cells nucleic acids are either: Deoxyribose nucleic acids (DNA) 1.3 NUCLEOTIDE AND NUCLEOSIDES OR Ribose nucleic acids (RNA) 1.4 DEOXYRIBOSE NUCLEIC ACID 1. Ribonucleic Acid (RNA) The pentose sugar is Ribose (has a hydroxyl group in the 2nd carbon---OH) 1.1 INTRODUCTION TO NUCLEIC ACID Involved in the transcription/translation of genetic material (DNA) NUCLEIC ACIDS Encodes or transfer information from The 4th type of macromolecule one bateria to another The chemical link between generations and source of genetic information in 5 TYPES OF RNA chromosomes Heterogenous nuclear RNA (hnRNA) Messenger RNA (mRNA) FUNCTION Small nuclear RNA (snRNA) Dictate the amino acid sequence in Transfer RNA (tRNA) proteins (sequence is important in order Ribosomal RNA (rRNA) to avoid mutation caused by any insertion and deletion) 2. Deoxyribonucleic Acid (DNA) Give in formation to chromosomes, The pentose sugar is Deoxyribose (has which is then passed from parent to a hydrogen-H, but the oxygen is absent) offspring Deoxy = minus oxygen. All life on earth uses the nucleic acid for Genetic material – sequence of the storage of genetic information nucleotides encodes different amino acids DNA controls all living processes including production of new cells – cell division Chromosomes are made of DNA 1.2 NUCLEOTIDE STRUCTURE Building blocks for DNA and RNA (each strand of DNA & RNA is a string of nucleotide) Intracellular source of energy – ATP Second messengers – involved in intracellular signaling (cAMP) Important in Intracellular signaling DNA is replicated/reproduced (DNA has switches (g proteins) the ability to encode high information, Despite the complexity and diversity of only four-letter code is used in the life, the structure of DNA is only making of our DNA). Identical copies of dependent on 4 different nucleotides. DNA are made (REPLICATION) Diversity is dependent on the nucleotide - DNA will be used in the formation or sequence transcription of RNA. Genetic messages Order of nucleotide bases determines are read and carried out of the cell the primary structure of the nucleic acid. nucleus to the ribosomes, where protein All nucleotides are 2 ring structures synthesis occurs. (TRANSCRIPTION) composed of - RNA (mRNA) is used in the formation 5 CARBON SUGAR: β-D-ribose (RNA) of protein sequences. Genetic messages and β-D-deoxyribose (DNA) are decoded to make proteins. (TRANSLATION) GROUP 6 (GAVANE, SALORIO, TAYABAS) || 1  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ NUMBER OF PHOSPHATE GROUPS DETERMINES NOMENCLATURE BASE: Purine and Pyrimidine Pyrimidine contains two pyridine-like nitrogen’s in a six-membered aromatic ring. PYRCUT AMP, ADP, and ATP Additional phosphate groups can be THYMINE – has a added to the nucleoside 5’ methyl and carboxyl monophosphates to form diphosphates group. (FOR DNA and triphosphates. ONLY) ATP is the major energy source for cellular activity. GUANINE – has an amine group URACIL – (FOR RNA ONLY) Purine has 4 N’s in a fused ring-like structure. Three are basic like pyridine-like and one is like that in pyrrole. PURGA ADENINE – has -Adenosine 5’ monophosphate forms two phosphates amine and 4 nitrogen and then with the removal of water adenosine 5’ diphosphate is formed. In every addition of water, GUANINE – has the removal of water also occurs. ATP Structure – amine, nitrogen, and five phosphate connected to a ribose sugar and a carboxyl group. pyrimidine. 1.3 NUCLEOTIDES AND NUCLEOSIDES PHOSPHATE GROUP: (bind directly on NUCLEOTIDES AND NUCLEOSIDES a sugar) A nucleotide WITHOUT a NUCLEOTIDE – composed of a nitrogenous phosphate group is a NUCLEOSIDE. base, pentose, and phosphate. (3-unit molecule) NUCLEOSIDE – composed of a nitrogenous base and pentose (does not contain phosphate) NUCLEOBASE – composed of a nitrogenous base (no sugar and phosphate) GROUP 6 (GAVANE, SALORIO, TAYABAS) || 2  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ Nucleosides are more soluble in water than free A nucleoside consists of a nitrogen base heterocyclic bases because of the hydrophilic linked by a glycosidic bond to Cl’ of a ribose nature of the pentose’s - OH groups. or deoxyribose. Named by changing the nitrogen base ending Important characteristics of the nucleoside to -osine for purines and -idine for formation process of combining two molecules pyrimidines. into one are: 1. The base is always attached to C1′ of the sugar (the anomeric carbon atom which is always in a b-configuration. For purine bases, attachment is through N9; for pyrimidine bases, N1 is involved. The bond connecting the sugar and base is a b-N-glycosidic linkage. 2. A molecule of water is formed as the two molecules bond together; a condensation reaction occurs NUCLEOTIDE AND NUCLEIC ACID NOMENCLATURE Eight nucleosides are associated with nucleic acid chemistry—four involve ribose (RNA nucleosides) and four involve deoxyribose (DNA nucleosides). The eight combinations are: PURGA: PURINE – ADENINE & GUANINE PYRCUT: PYRIMIDINE – CYTOSINE – URACIL - THYMINE NUCLEOTIDE FORMATION - Nucleotides are nucleosides that have a NUCLEOSIDE FORMATION phosphate group bonded to the pentose sugar present. The following structural A nucleoside is a two-subunit molecule equation is representative of the in which a pentose sugar is bonded to a conversion of a nucleoside to a nitrogen-containing heterocyclic base. nucleotide. The following structural equation is representative of nucleoside formation. -After the formation of nucleoside, the fifth carbon on the sugar will bind to the phosphate, removing one molecule of water. Then a 3-subunit entity called nucleotide will be - A pentose sugar is bonded to a formed. nitrogen-containing heterocyclic base to form a -Many Nucleotide will form a Nucleic Acid two-unit molecule called nucleoside. GROUP 6 (GAVANE, SALORIO, TAYABAS) || 3  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ HYDROGEN BONDING INTERACTIONS Two bases can hydrogen bond to form a base pair For monomers, a large number of base pairs is possible In polynucleotide, only few possibilities exist Watson-crick base pairs predominate in double-stranded DNA A pair with T Important characteristics of the nucleotide formation C pair with G process of adding a phosphate group to a nucleoside Purine pairs with Pyrimidine are the following: 1. The phosphate group is attached to the sugar at BASE PAIRING DNA: THE WATSON-CRICK the C5′ position through a phosphoester linkage. MODEL 2. As with nucleoside formation, a molecule of water In 1953 Watson and Crick noted that is produced in nucleotide formation. Thus, overall, DNA consists of two polynucleotide two molecules of water are produced in combining a strands running in opposite directions sugar. and coiled around each other in a double helix 1.4 DEOXYRIBOSE NUCLEIC ACID (DNA) Strands are held together by hydrogen bonds between specific pairs of bases DNA stands for deoxyribose nucleic acid Adenine and Thymine form strong Chemical substance present in the hydrogen bonds to each other but not to nucleus of all cells in all living organisms C or G DNA controls all the chemical changes Guanine and Cytosine form strong which take place in cells hydrogen bonds to each other but not to Muscle, blood, nerve, and all cell are A or T controlled by DNA. The strands of DNA is complementary A very large molecule made up of long because of H- bonding chain of subunits called Nucleotides. Whenever a G occurs in one strand, a C Each nucleotide is made up of sugar, occurs opposite in the other strand and phosphate and base. likewise with A and T Nucleic acids are biopolymers made of Phosphodiester Link when one nucleotide nucleotides aldopentoses linked to a purine or interacts with one nucleotide. pyrimidine and a phosphate. MANY NUCLEOTIDES = NUCLEIC ACID GROUP 6 (GAVANE, SALORIO, TAYABAS) || 4  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ At third carbon, the phosphate bounds to another nucleotide linked by the 3rd and 5th position though the phosphate – serves as the bridge. PRIMARY STRUCTURE OF NUCLEIC ACIDS The primary structure of nucleic acid is the nucleotide sequence The nucleotides in nucleic acids are joined by phosphodiester bonds. The 3’-OH group of the sugar in one nucleotide forms ann ester bond to the phosphate group on the 5’-carbon of the sugar of the next nucleotide. Reading Primary Structure A nucleic acid polymer has a free 5’-phosphate group at one end and a free 3’-OH group at the other end The sequence is read from the free 5’-end using the letters of the bases This example reads 5’-A-C-G-T-3’ PROPERTIES OF A DNA DOUBLE HELIX – SECONDARY STRUCTURE/3D The strands of DNA are anti parallel The strands are complimentary There are hydrogen bond forces There are base stacking interactions There are 10 base pairs per turn GROUP 6 (GAVANE, SALORIO, TAYABAS) || 5  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ OUTLINE 2.1 Describing a 2.6 Prediciting Base sequence Sequence 2.2 Secondary 2.7 Nucleic Acid Structure Structure: The double helix 2.3 Properties of a DNA 2.8 Dna replication double helix-secondary-structu re/3D 2.4 Model of DNA 2.9 Nucleic Acid structure Polymerization ➔ The sides of the ladder are: 2.5 Nucleic Acid P=phosphate Structure “Base S=sugar molecule Pairing” ➔ The steps of the ladder are C, G, T, A = nitrogenous bases (Nitrogenous means containing the element 2.1 DESCRIBING A SEQUENCE nitrogen.) Describing a sequence A=adenine (Apples are Tasty) ➔ Chain is described from 5’end, identifying T=thymine the bases in order of occurrence, using the A always pairs with T in DNA abbreviations A for Adenosine, G for C=cytosine (Cookies are Good) Guanosine, C for Cytidine, and T for Thymine G=guanine (or U for Uracil in RNA). C always pairs with G in DNA ➔ A typical sequence is written as TAGGCT Hydrogen bonding possibilities are more 2.2 SECONDARY STRUCTURE favorable when A-T and C-G base pairing Secondary Structure: DNA Double Helix occurs ➔ In DNA there are two strands of nucleotides ➔ Base-paring combinations that do occur that wind together in a double helix. The strand run in opposite directions The bases are arranged in step-like pairs The base pairs are held together by hydrogen bonding ➔ The pairing of the bases from the two strands is very specific ➔ The complimentary base pairs are A-T and G-C ➔ Base-pairing combinations that do not occur two hydrogen bonds form between A and T three hydrogen bonds form between G and C ➔ Each pair consists of a purine and a pyrimidine, so they are the same width, keeping the two strands at equal distances from each other. 2.3 PROPERTIES OF A DNA DOUBLE HELIX-SECONDARY-STRUCTURE/3D 2.4 MODEL OF DNA Properties of a DNA double Model of DNA: helix-Secondary-Structure/3D ➔ The model was developed by Watson and ➔ The strands of DNA are antiparallel Crick in 1953. ➔ The strands are complimentary ➔ They received a nobel prize in 1962 for ➔ There are hydrogen bond forces their work. ➔ There are base stacking interactions ➔ The model looks like a twisted ladder – ➔ There are 10 bases pairs per turn double helix. GROUP 6 (GAVANE, SALORIO, TAYABAS) || 6  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ 2.5 NUCLEIC ACID STRUCTURE “BASE 2.8 DNA REPLICATION PAIRING” DNA replication Nucleic Acid Structure “Base Pairing” ➔ Before a cell divides, the DNA strands ➔ DNA base-pairing is antiparallel unwind and separate i.e. 5’ - 3’ (l-r) on top: 5’ - 3’ (r-l) on ➔ Each strand makes a new partner by adding the appropriate nucleotides ➔ The result is that there are now two double-stranded DNA molecules in the nucleus ➔ So that when the cell divides, each nucleus contains identical DNA When a eukaryotic cell divides, the process is called mitosis ➔ the cell splits into two identical daughter cells ➔ the DNA must be replicated so that each daughter cell has a copy DNA replication involves several processes: ➔ first, the DNA must be unwound, separating the two strands ➔ the single strands then act as templates for synthesis of the new strands, which are complimentary in sequence ➔ bases are added one at a time until two new DNA strands that exactly duplicate the original DNA are produced 2.6 PREDICTING BASE SEQUENCE Step 1 ➔ Hydrogen bonds between base pairs are broken by the enzyme DNA helicase and DNA molecule unzips ➔ DNA molecule separates into complementary halves ➔ Practice DNA base pairs GATTACA CTAATGT 2.7 NUCLEIC ACID STRUCTURE: THE DOUBLE HELIX Step 2 ➔ Nucleotides match up with complementary bases GROUP 6 (GAVANE, SALORIO, TAYABAS) || 7  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ Step 3 ➔ Nucleotides are linked into 2 new strands of DNA by theenzyme, polymerase—DNA polymerase also proofreadsfor copying errors Mutations occur when copying errors cause a change in the sequence of DNA nucleotide bases 2.9 NUCLEIC ACID STRUCTURE GROUP 6 (GAVANE, SALORIO, TAYABAS) || 8  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ 5’-3’ester bonds of the leading strand OUTLINE The lagging strand, which grows in the 3’-5’ 3.1 SEMI-CONSERVATIVE REPLICATION direction, is synthesized in short sections called Okazaki fragments 3.2 STORAGE OF DNA The Okazaki fragments are joined by DNA ligase to give a single 3’-5’ DNA strand Spaces between “nicks” 3.3 DIRECTION OF REPLICATION 3.4 RNA MOLECULES 3.4 RNA MOLECULES COMPOSITION 3.5 TYPES OF RNA MOLECULES 1. Ribose sugar (with O in 3rd carbon) 2. Phosphate group 3.1 SEMI-CONSERVATIVE REPLICATION 3. One of 4 types of bases (all containing nitrogen): - Adenine - Uracyl (only in RNA) - Cytosine - Guanine RNA—Ribonucleic Acid RNA is a messenger that allows the instruction of DNA to bedelivered to the rest of the cell RNA is different than DNA: 1. The sugar in RNA is ribose; the sugar in DNA is deoxyribose 2. RNA is a single strand of nucleotides; DNA is a double strand of nucleotides 3. RNA has Uracil (U) instead of Thymine (T) which is in The process is called semi-conservative replication DNA because 4. RNA is found inside and outside of the nucleus; one strand of each daughter DNA comes from the parent DNA is DNA and found only inside the nucleus onestrand is new The energy for the synthesis comes from There are three main types of RNA: hydrolysis of 1. ribosomal (rRNA) phosphate groups as the phosphodiester bonds form 2. messenger (mRNA) between the bases. 3. transfer (tRNA) - subtypes: heterogenous nuclear RNA (hnRNA) & small 3.2 STORAGE OF DNA nuclear In eukaryotic cells (animals, plants, fungi) DNA RNA (snRNA) is stored in the nucleus, which is separated from the rest of the cell by asemipermeable 3.5 TYPES OF RNA MOLECULES membrane The DNA is only organized into chromosomes during cell replication Between replications, the DNA is stored in a compact ballcalled chromatin, and is wrapped around proteins called histones to form nucleosomes 3.3 DIRECTION OF REPLICATION Messenger RNA carries the genetic code to the ribosomes - they are strands of RNA that are complementary to the DNA of The enzyme helicase unwinds several sections the gene for the protein to be synthesized of parent DNA Transfer RNA translates the genetic code from the messenger At each open DNA section, called a replication RNA and brings specific amino acids to the ribosome for fork, DNA polymerase catalyzes the formation of GROUP 6 (GAVANE, SALORIO, TAYABAS) || 9  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ protein synthesis Each amino acid is recognized by one or more specific tRNA tRNA has a tertiary structure that is L-shaped - one end attaches to the amino acid and the other binds to the mRNA by a 3-base complimentary sequence PARTS OF TRANSFER RNA There are 61 different tRNAs, one for each of the 61 codons that specifies an amino acid tRNA has 70-100 ribonucleotides and is bonded to a specific amino acid by an ester linkage through the 3′ hydroxyl on ribose at the 3′ end of the tRNA Each tRNA has a segment called an anticodon, a codon sequence Ribosomes are the sites of protein synthesis -they consist of ribosomal DNA(65%) and proteins (35%) - they have two subunits, a large one and a small one GROUP 6 (GAVANE, SALORIO, TAYABAS) || 10  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ OUTLINE 4.1 HOW DNA WORKS 4.2 TRANSCRIPTION PROCESS 4.3 PROTEIN SYNTHESIS 4.4 RNA POLYMERASE 4.5 PROCESSING OF mRNA Example of RNA Primary Structure 4.6 SPLICING In RNA, A, C, G, and U are linked by 3’-5’ ester bonds between ribose and phosphate 4.1 HOW DNA WORKS 1. DNA stores genetic information in segments called genes 2. The DNA code is in Triplet Codons (short sequences of 3 nucleotides each) 3. Certain codons are translated by the cell into certain Amino acids. 4. Thus, the sequence of nucleotides in DNA indicate a sequence of Amino acids in a protein. 4.2 TRANSCRIPTION PROCESS Several turns of the DNA double helix unwind, exposing the bases of the two strands Ribonucleotides line up in the proper order by hydrogen bonding to their complementary bases on DNA Bonds form in the 5 3 direction, 4.3 PROTEIN SYNTHESIS The two main processes involved in protein synthesis are the formation of mRNA from DNA (transcription) the conversion by tRNA to protein at the ribosome (translation) Transcription takes place in the nucleus, while translation takes place in the cytoplasm Transcription of RNA from DNA Genetic information is transcribed to form mRNA Only one of the two DNA strands is transcribed much the same way it is replicated during cell into mRNA The strand that contains the gene is the coding or sense strand The strand that gets transcribed is the template or antisense strand The RNA molecule produced during transcription is a copy of the coding strand (with U in place of T) division GROUP 6 (GAVANE, SALORIO, TAYABAS) || 11  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ The exons that remain are joined to form the mRNA that leaves the nucleus with the information for the synthesis of protein 4.4 RNA POLYMERASE During transcription, RNA polymerase moves along theDNA template in the 3’-5’direction to synthesize thecorresponding mRNA The hnRNA is released at the termination point 4.6 SPLICING Process of removing introns from an hnRNA molecule and joining the remaining exons together to form an mRNA molecule. The process involves the snRNA which facilitates splicing to occur. snRNA is found complexed with protein together called small nuclear ribonucleoprotein particles snRNPs (pronounced as snurps) A large complex of snurps is called a spliceosome. Spliceosome is a large assembly of snRNA molecules and proteins involved in the conversion of hnRNA molecules to mRNA molecules 4.5 PROCESSING OF mRNA Genes in the DNA of eukaryotes contain exons thatcode for proteins along with introns that do not Because the initial mRNA, called a pre-RNA/hnRNA includes the noncoding introns, it must be processed before it can be read by the Trna While the mRNA is still in the nucleus, the introns are removed from the pre-RNA GROUP 6 (GAVANE, SALORIO, TAYABAS) || 12 BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ \ GROUP 6 (GAVANE, SALORIO, TAYABAS) || 13  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ deoxyribose, becomes incorporated into the new nucleic acid backbone. OUTLINE 3. RNA polymerase is involved in the linkage of ribonucleotides, one by 5.1 TRANSCRIPTION 5.6 GENETIC CODE one, to the growing hnRNA molecule. 5.2 STEPS IN 5.7 mRNA CODONS 4. Transcription ends when the RNA TRANSCRIPTION AND ASSOCIATED polymerase enzyme encounters a PROCESS AMINO ACIDS sequence of bases that is “read” as a stop signal. The newly formed 5.3 DNA-RNA BASE 5.8 READING THE hnRNA molecule and the RNA PAIRING: THE GENETIC CODE polymerase enzyme are released, and COMPLEMENTARY the DNA then rewinds to re-form the BASE PAIRS original double helix. 5.4 REGULATION OF 5.9 THE STRUCTURE TRANSCRIPTION OF tRNA 5.5 5.10 tRNA AND RIBONUCLEOTIDES ANITCODON 5.1 TRANSCRIPTION Is the process by which DNA directs the synthesis of hnRNA/mRNA molecules that carry the coded information needed for protein synthesis. Figure 22-16 The transcription of DNA to form hnRNA involves an unwinding of a portion of the 5.2 STEPS IN TRANSCRIPTION PROCESS DNA double helix. Only one strand of the DNA is copied during transcription. Several steps occur during transcription: (ppt) The strand of DNA used for I. a section of DNA containing the gene hnRNA/mRNA synthesis is called the unwinds (governed by RNA polymerase). template strand. It is copied proceeding II. one strand of DNA is copied starting at in the 3′-to-5′ direction. The other DNA the initiation point, which has the strand (the non-template strand) is sequence TATAAA. called the informational strand. The III. an hnRNA is synthesized using informational strand, although not complementary base pairing with uracil involved in RNA synthesis, gives the (U) replacing thymine (T). base sequence present in the hnRNA IV. the newly formed mRNA moves out of strand being synthesized (with the the nucleus to ribosomes in the exception of U replacing T). cytoplasm and the DNA re-winds. Figure 22-16 shows the overall process of transcription of DNA to form hnRNA. (book) 1. A portion of the DNA double helix unwinds, exposing a sequence of bases (a gene). The unwinding process is governed by the enzyme, “RNA polymerase” rather than DNA helicase (a replication enzyme). 2. Free ribonucleotides, one nucleotide at a time, align along one of the exposed strands of DNA bases, the template strand, forming new based pairs. In this process, U rather than T aligns with A in Figure 31.14 A polyribosome consists of several the base-pairing process. Only about 10 ribosomes simultaneously translating one mRNA. base pairs of the DNA template strand are exposed at a time. Because ribonucleotides rather than deoxyribonucleotides are involved in the base pairing, ribose, rather than GROUP 6 (GAVANE, SALORIO, TAYABAS) || 14  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ There are also codons that signal the 5.3 DNA-RNA BASE PAIRING: THE “start” and “end” of a polypeptide chain. COMPLEMENTARY BASE PAIRS The amino acid sequence of a protein can be determined by (1) reading the DNA RNA triplets in the DNA sequence that are complementary to the codons of the A U mRNA, or (2) directly from the mRNA sequence. G C The entire DNA sequence of several organisms, including humans, have been C G determined, however, T A -only primary structure can be determined this way. -doesn’t give tertiary structure or “RNA molecules contain the base U instead of protein function. the base T.” GENETIC CODE 1 5.4 REGULATION OF TRANSCRIPTION ❖ The sequence of bases in DNA forms the, A specific mRNA is synthesized when the “Genetic Code.” cell requires a particular protein ❖ A group of three bases (a triplet) controls the The synthesis is regulated at the production of a particular amino acid in the cytoplasm of the cell. transcription level: ❖ The different amino acids and the order in which they are joined up determines the sort - feedback control, where the end of protein being produced. products speed up or slow the synthesis CODING of mRNA Example: - enzyme induction, where a high level of a reactant induces the transcription process to provide the necessary enzymes for that reactant Regulation of transcription in eukaryotes is complicated and we will not study it here. 5.5 RIBONUCLEOTIDES TRIPLE CODE Each triplet codes for a specific amino acid: The amino acids are joined together in the correct sequence to make part of a protein: 5.6 GENETIC CODE The genetic code is found in the sequence of nucleotides in mRNA that is translated from the DNA. A codon is a triplet of bases along the mRNA that codes for a particular amino acid. Each of the 20 amino acids needed to build a protein has at least 2 codons. GROUP 6 (GAVANE, SALORIO, TAYABAS) || 15  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ 5.7 mRNA CODONS AND ASSOCIATED AMINO 5.9 THE STRUCTURE OF tRNA ACIDS 5.10 tRNA AND ANTICODON 5.8 READING THE GENETIC CODE Suppose we want to determine the amino acids coded for in the following section of a mRNA 5’—CCU —AGC—GGA—CUU—3’ According to the genetic code, the amino acids for these codons are: CCU = Proline AGC = Serine GGA = Glycine CUU = Leucine The mRNA section codes for the amino acid sequence of Pro—Ser—Gly—Leu Figure 22-19 A tRNA molecule. The amino acid attachment site is at the open end of the cloverleaf (the 3′ end), and the anticodon is located in the hairpin loop opposite the open end. Figure 22-21 The interaction between anticodon (tRNA) and codon (mRNA), which involves complementary base pairing, governs the proper placement of amino acids in a protein. GROUP 6 (GAVANE, SALORIO, TAYABAS) || 16 BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ GROUP 6 (GAVANE, SALORIO, TAYABAS) || 17  BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ 6.3 INITIATION OUTLINE 6.1 TRANSLATION AND tRNA ACTIVATION 6.2 INITIATION AND TRANSLOCATION 6.3 INITIATION 6.4 ELONGATION 6.5 TERMINATION 6.1 TRANSLATION AND tRNA ACTIVATION Transcription Once the DNA has been transcribed to mRNA, the codons must be translated to the amino acid sequence of the protein The first step in translation is activation of the tRNA Each tRNA has a triplet called an anticodon that complements a codon on mRNA An aminoacyl tRNA synthetase enzyme uses ATP hydrolysis to attach an amino acid to a specific tRNA 6.4 ELONGATION 6.2 INITIATION AND TRANSLOCATION Initiation of protein synthesis occurs when a mRNA attaches to a ribosome On the mRNA, the start codon (AUG) binds to a tRNA with methionine The second codon attaches to a tRNA with the next amino acid A peptide bond forms between the adjacent amino acids at the first and second codons The first tRNA detaches from the ribosome and the ribosome shifts to the adjacent codon on the mRNA (this process is called translocation) A third codon can now attach where the second one was before translocation GROUP 6 (GAVANE, SALORIO, TAYABAS) || 18 BS NURSING LEVEL 1: BIOCHEMISTRY LECTURE (MC 2 LEC) TOPIC 4: NUCLEIC ACID MS. ANGELICA LOPEZ 6.5 TERMINATION GROUP 6 (GAVANE, SALORIO, TAYABAS) || 19