DNA and RNA

I. DNA Structure Double Helix In the early 1950s, American James Watson and Britain Francis Crick determined that DNA is in the shape of a double helix. Rosalind Franklin’s and Maurice Wilkins’s photographs and crystals led to Watson and Cricks DNA models. Double Helix In the early 1950s, American James Watson and Britain Francis Crick determined that DNA is in the shape of a double helix. Rosalind Franklin’s and Maurice Wilkins’s photographs and crystals led to Watson and Cricks DNA models.

A. DNA Nucleotides A nucleotide is two long chains or strands of repeating subunits. Is made of three parts: A five-carbon sugar (deoxyribose) A phosphate group (P bonded to 4 O) A nitrogenous base (made up of N and C) A nucleotide is two long chains or strands of repeating subunits. Is made of three parts: A five-carbon sugar (deoxyribose) A phosphate group (P bonded to 4 O) A nitrogenous base (made up of N and C)

B. The Bonds of DNA Covalent Bonds hold the sugar of one nucleotide to the phosphate group of the next nucleotide to form the chains. Hydrogen bonds join the bases on one strand of DNA to the bases on the other strand. Usually 2 or 3 bonds. Covalent Bonds hold the sugar of one nucleotide to the phosphate group of the next nucleotide to form the chains. Hydrogen bonds join the bases on one strand of DNA to the bases on the other strand. Usually 2 or 3 bonds.

C. The Nitrogenous Bases Purines (double ring) Adenine (A) Guanine (G) Pyrimidines (single ring) Cytosine (C) Thymine (T) Purines (double ring) Adenine (A) Guanine (G) Pyrimidines (single ring) Cytosine (C) Thymine (T)

D. Complementary Bases Base-pairing rules Each pairing contains one purine and one pyrimidine Guanine with Cytosine (G-C) Adenine with Thymine (A-T) The order of nitrogenous bases on a chain of DNA is its base sequence. Base-pairing rules Each pairing contains one purine and one pyrimidine Guanine with Cytosine (G-C) Adenine with Thymine (A-T) The order of nitrogenous bases on a chain of DNA is its base sequence.

II. DNA Replication The process by which DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission. Mutations occur at a very low frequency (about one in every billion paired nucleotides). Some mutations cause disease such as cancer. Figure in Modern Biology © 2006 The process by which DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission. Mutations occur at a very low frequency (about one in every billion paired nucleotides). Some mutations cause disease such as cancer. Figure in Modern Biology © 2006

Notice the direction of the synthesis

Steps of DNA Replication (Semi-Conservative Replication) 1. Helicase separates the DNA strands resulting in a replication fork. DNA is unzipped. 2. Complementary nucleotides are added to each of the original DNA strands. Gaps are joined together by DNA ligase. 3. Two DNA molecules, each made up of one new strand and one old strand, identical to the original DNA molecule result. 1. Helicase separates the DNA strands resulting in a replication fork. DNA is unzipped. 2. Complementary nucleotides are added to each of the original DNA strands. Gaps are joined together by DNA ligase. 3. Two DNA molecules, each made up of one new strand and one old strand, identical to the original DNA molecule result.

III. Protein Synthesis Ribonucleic acid, RNA, plays a role in protein synthesis. Central Concept DNA RNA protein Ribonucleic acid, RNA, plays a role in protein synthesis. Central Concept DNA RNA protein

A. RNA Structure & Function Differences in RNA than in DNA Sugar ribose instead of deoxyribose Nitrogenous base uracil instead thymine Single stranded instead of double stranded Shorter than DNA Differences in RNA than in DNA Sugar ribose instead of deoxyribose Nitrogenous base uracil instead thymine Single stranded instead of double stranded Shorter than DNA

Types of RNA Messenger RNA (mRNA) – carries instructions from a gene to make a protein Ribosomal RNA (rRNA) – part of the structure of ribosomes Transfer RNA (tRNA) – transfer amino acids to the ribosomes to make a protein Messenger RNA (mRNA) – carries instructions from a gene to make a protein Ribosomal RNA (rRNA) – part of the structure of ribosomes Transfer RNA (tRNA) – transfer amino acids to the ribosomes to make a protein

B. Transcription The process by which the genetic instructions in a specific gene are transcribed into an RNA molecule. Takes place in the nucleus of eukaryotic cells and in the DNA-containing region in the cytoplasm of prokaryotic cells. Figure of Prentice Hall Biology The process by which the genetic instructions in a specific gene are transcribed into an RNA molecule. Takes place in the nucleus of eukaryotic cells and in the DNA-containing region in the cytoplasm of prokaryotic cells. Figure of Prentice Hall Biology

RNA Editing After the RNA is produced, it must be edited before it can be used. Introns are removed and exons are spliced together before the RNA leaves the nucleus. After the RNA is produced, it must be edited before it can be used. Introns are removed and exons are spliced together before the RNA leaves the nucleus.

C. The Genetic Code The term for the rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid. Three adjacent nucleotides (“letters”) in mRNA specify an amino acid (“word”) Three adjacent nucleotides are called a codon and encodes for an amino acid or signifies a start or stop signal. The term for the rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid. Three adjacent nucleotides (“letters”) in mRNA specify an amino acid (“word”) Three adjacent nucleotides are called a codon and encodes for an amino acid or signifies a start or stop signal.

No codon encodes more than one amino acid. The are 64 possible codons and amino acids are can be specified by more than one codon. A start codon is a specific sequence of nucleotides in mRNA that indicates where translation should begin. AUG. Three stop codons are specific sequences of nucleotides in mRNA that indicates where translation should end. No codon encodes more than one amino acid. The are 64 possible codons and amino acids are can be specified by more than one codon. A start codon is a specific sequence of nucleotides in mRNA that indicates where translation should begin. AUG. Three stop codons are specific sequences of nucleotides in mRNA that indicates where translation should end.

Figure 12-17

D. Translation Decoding of the genetic instructions to form a polypeptide Takes place on the surface of the ribosome Protein structure Made of one or more polypeptides Polypeptides are chains of amino acids linked by peptide bonds. Only 20 different amino acids The amino acids sequence determines how the polypeptides will twist and fold into the protein. The shape of the protein is critical to its function. Decoding of the genetic instructions to form a polypeptide Takes place on the surface of the ribosome Protein structure Made of one or more polypeptides Polypeptides are chains of amino acids linked by peptide bonds. Only 20 different amino acids The amino acids sequence determines how the polypeptides will twist and fold into the protein. The shape of the protein is critical to its function.

Translation Figure Beginning at the start codon, tRNA carrying an amino acid pairs its anticodons pair up with the complementary codon on the mRNA. This continues as an assembly line linking the amino acids and breaking bonds between the tRNA and the amino acids. The linked amino acids form an polypeptide until a stop codon is reached. Figure Beginning at the start codon, tRNA carrying an amino acid pairs its anticodons pair up with the complementary codon on the mRNA. This continues as an assembly line linking the amino acids and breaking bonds between the tRNA and the amino acids. The linked amino acids form an polypeptide until a stop codon is reached.

E. The Human Genome A genome is the complete genetic content. Biologists have now decoded the order of the 3.2 billion base pairs in the 23 human chromosomes. Bioinformatics compares different DNA sequences to try to determine what information the DNA codon encodes. A genome is the complete genetic content. Biologists have now decoded the order of the 3.2 billion base pairs in the 23 human chromosomes. Bioinformatics compares different DNA sequences to try to determine what information the DNA codon encodes.

DNA Gene – Short Segment of double helix Nitrogen Base – the “rung on the ladder” Deoxyribose – “sugar side of the ladder” Nucleotide – composed of 3 parts floating free in the cytoplasm DNA – the double helix

End of Chapter 10 Notes