THE DNA/PROTEIN CONNECTION MOLECULAR GENETICS THE DNA/PROTEIN CONNECTION   Regents Biology

Upon completion of this unit students will be able to: OBJECTIVES Upon completion of this unit students will be able to:   1. State who discovered the structure of DNA. 2. Describe the structure of a nucleotide. 3. Describe the structure of a DNA molecule. 4. List the 4 different nitrogen bases found in DNA. 5. Explain what is meant by complementary base pairing. 6. Describe the structure of RNA and list 3 ways it differs from DNA. 7. Recognize that DNA (deoxyribonucleic acid) controls cellular activity by directing the production of important protein molecules such as enzymes. 8. Explain how proteins are synthesized from a DNA template. 9. Define the terms transcription and translation. 10. Explain the role of mRNA, rRNA, tRNA in the process of protein synthesis. 11. Correctly define the terms triplet, codon, and anticodon. 12. Recognize that the work of a cell is carried out by the many different kinds of molecules it assembles (i.e., proteins). 13. Understand that proteins are long, folded molecules composed of up to 20 different kinds of amino acids which interact to produce specific protein shapes. 14. Recognize that enzymes and hormones are proteins. 15. Recognize that the specific shape of a protein usually determines its function. 16. Understand that 20 amino acids can be arranged to form a countless number of proteins with various shapes and functions. (letters : words AS amino acids : proteins) KEY WORDS

INTRODUCTION We know that: 1.CHROMOSOMES carry the genetic information 2.Genetic information is arranged in distinct units, called GENES, along the chromosomes 3.There are two types of nucleic acids: DNA - DEOXYRIBONUCLEIC ACID; FOUND ONLY IN THE NUCLEUS RNA - RIBONUCLEIC ACID; FOUND MAINLY IN THE CYTOPLASM 4.Chromosomes contain protein and DNA; the hereditary material of the chromosomes is DNA, not protein

A. KEY EXPERIMENTS Griffith (1928) and Avery, MacLeod, and McCarthy (1944) – found that a substance from dead pneumonia bacteria could change harmless pneumonia bacteria into pneumonia-causing ones; Griffith concluded that some “transforming factor” from dead Type S bacteria changed Type R bacteria into Type S. Avery, MacLeod, and McCarthy concluded that the “transforming factor” was DNA

2. Hershey and Chase (1952) – A bacteriophage is a VIRUS THAT INFECTS BACTERIA. Hershey and Chase found that the genetic material in the two viruses they used was in fact DNA.

BASE SUGAR PHOSPHATE GROUP (PO4) B. COMPOSITION OF DNA Levene found that a DNA molecule is made up of: 1.       5-CARBON SUGAR (DEOXYRIBOSE) 2.       PHOSPHATE GROUP 3.       NITROGENOUS BASE (ADENINE [A], GUANINE [G], CYTOSINE [C], THYMINE [T]) DNA contains ONE sugar, ONE phosphate, and ONE base; these 3 subunits make up one unit called a NUCLEOTIDE N U C L E O T I D BASE (A,T,C or G) SUGAR (DEOXYRIBOSE) PHOSPHATE GROUP (PO4)

·      Since there are four different bases (adenine, thymine, guanine, cytosine), there are 4 different nucleotides ·      Diagram of nucleotide:

 C. LOCATION OF DNA DNA is a NUCLEIC ACID that is located in the NUCLEUS of every cell. Within the nucleus, the DNA molecule is tightly coiled into structures called CHROMOSOMES.

 D. STRUCTURE OF DNA WATSON AND CRICK were credited with finding the structure of the DNA molecule The DNA molecule is a DOUBLE HELIX and has a “sugar-phosphate” backbone

BASE PAIR RULE: A bonds with T C bonds with G The two strands are complementary: BASE PAIR RULE: A bonds with T C bonds with G

E. DNA REPLICATION Bases are held together by weak, hydrogen bonds:   When DNA replicates itself, it almost looks like a zipper unzipping; free nucleotides from the nucleus attach to their COMPLEMENTARY BASE and form a new strand of DNA Enzymes are needed to make this process happen. HELICASE separates the chains and DNA POLYMERASE assemble new chains of DNA by using the nucleotides floating free in the cytoplasm

BASE SUGAR PHOSPHATE GROUP (PO4) F. COMPOSITION AND STRUCTURE OF RNA RNA contains: 1.       5-CARBON SUGAR (RIBOSE) 2.       PHOSPHATE GROUP 3. NITROGENOUS BASE (ADENINE [A], GUANINE [G], CYTOSINE [C], URACIL [U]) BASE (A,U,C or G) SUGAR (RIBOSE) PHOSPHATE GROUP (PO4)

II. GENES AND ENZYMES Every chemical reaction in living cells requires a specific ENZYME; these enzymes must be MADE Hereditary material acts by controlling the SYNTHESIS of cell enzymes A. One gene, one enzyme hypothesis: EACH GENE PRODUCES ITS EFFECTS BY CONTROLLING THE SYNTHESIS OF A PARTICULAR ENZYME B. One gene, one polypeptide hypothesis: EACH GENE CONTROLS THE SYNTHESIS OF A PARTICULAR CHAIN OF AMINO ACIDS (POLYPEPTIDEPROTEIN)

III. PROTEIN SYNTHESIS The RIBOSOME is the site of protein synthesis. It uses the mRNA, which carries the code from DNA to do this. Since DNA is too big to leave the nucleus and cannot go to the nucleus itself, RNA carries the MESSAGE which will eventually make the protein. There are 2 stages to protein synthesis: 1. TRANSCRIPTION – The COPYING of a MESSAGE (segment of DNA that contains the information to build a particular protein) from DNA to mRNA TRANSCRIPTION occurs in the NUCLEUS 2. TRANSLATION - The process by which the information coded in mRNA is used to synthesize a protein. TRANSLATION occurs in the CYTOPLASM at the RIBOSOME

THE FLOW OF GENETIC INFORMATION IS:   THE FLOW OF GENETIC INFORMATION IS: DNA  RNA  PROTEIN

 A. THE GENETIC CODE A chain of amino acids = POLYPEPTIDE = protein Each gene directs the SYNTHESIS of a particular polypeptide chain and specifies how the amino acids are assembled The sequence of bases along DNA is THE CODE that specifies the order of amino acids, thus determining the protein being made There are 20 amino acids, and the 4 bases make up the 64 different 3-letter sequences GENE = LONG STRING OF BASES ALONG A DNA MOLECULE Each group of three bases is a CODE for a specific amino acid along a polypeptide chain (also known as a CODON)

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B. TYPES OF RNA 1. Messenger RNA (mRNA) mRNA carries the “message”, or CODE, for a polypeptide DNA strands separate (like the zipper) and complementary RNA nucleotides attach to the DNA; this is called TRANSCRIPTION

At the end of the message, the DNA and mRNA strands detach The copying of a genetic code from DNA  mRNA is called TRANSCRIPTION Each group of 3 bases that specifies for a specific amino acid is called a CODON   DNA  DNA is DNA REPLICATION DNA  mRNA is TRANSCRIPTION

2. Transfer RNA (tRNA) Structure of tRNA  Each type of tRNA molecule will pick up ONE type of AMINO ACID, depending on the nucleotides Since there are 20 different kinds of amino acids, there are 20 different forms of tRNA The ANTICODON is the complement of a specific mRNA codon tRNA brings a particular amino acid to a particular place specified by mRNA The process of assembling polypeptides from information encoded in the mRNA with the aid of tRNA  

3. Ribosomal RNA (rRNA) rRNA is RNA that is formed by DNA IN THE NUCLEUS OF THE CELL ASSEMBLY OF POLYPEPTIDE (PROTEIN) Synthesis of mRNA, tRNA, and rRNA and the assembly of ribosomes happen in the NUCLEUS Steps to the assembly of a polypeptide (protein):

1.mRNA is made from DNA in the NUCLEUS. 2. mRNA moves out into the CYTOPLASM. 3. In the cytoplasm, AMINO ACIDS become attached to specific tRNA‘s 4. Ribosomes become attached to each strand of mRNA 5. Where a ribosome is attached to mRNA, a complementary tRNA ANTICODON attaches to the mRNA CODON 6. Ribosome moves along to the next codon 7. New tRNA attaches to mRNA strand and its amino acid joins the POLYPEPTIDE CHAIN 8. tRNA is released to pick up amino acids and repeats the cycle 9. Amino acids are added to the polypeptide chain until the ribosome reaches a “STOP” CODON 10. The polypeptide is released and assembles itself into a complete protein molecule

Genes to proteins Every step of translating DNA into a polypeptide chain requires a specific ENZYME; and all of these enzymes are specified by DNA

MOLECULAR GENETICS REVIEW 1. DNA stands for D EOXYRIBONUCLEIC ACID.   1. DNA stands for D EOXYRIBONUCLEIC ACID. 2. DNA is made up of small units called NUCLEOTIDES . 3. Each NUCLEOTIDE is made up of a: ·        DEOXYRIBOSE sugar ·        PHOSPHATE group ·        Nitrogen BASE 4. A nucleotide can contain one of the four different bases called: ·        ADENINE ·        THYMINE ·        CYTOSINE ·        GUANINE 5. According to the BASE PAIR RULE, the base ADENINE can only bond with THYMINE and CYTOSINE can only bond with GUANINE

  DNA is tightly coiled into structures called CHROMOSOMES. CHROMOSOMES are located within the NUCLEUS of every cell. The name used to describe 3 bases of DNA that code for a specific amino acid is the TRIPLET CODE. The process of transferring the genetic code from mRNA to an amino acid sequence is called TRANSLATION. The scientists who developed the double helix model of DNA are WATSON and CRICK. The nitrogenous base that can only pair with cytosine is GUANINE. The site of protein synthesis within a cell is the RIBOSOME. The weak chemical bonds between the bases of DNA are HYDROGEN bonds. The process of copying the genetic code from DNA to RNA is called TRANSCRIPTION. The triplet code of bases found on mRNA that bond to the anticodon is the CODON.