DNA and RNADNA and RNA

I. DNA StructureI. DNA Structure

Double HelixIn 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 HelixIn 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 NucleotidesA. 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 DNAB. 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 BasesC. 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 BasesD. Complementary Bases

Base-pairing rulesEach pairing contains one purine and

one pyrimidineGuanine 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 rulesEach pairing contains one purine and

one pyrimidineGuanine 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 ReplicationII. 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 10-10 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 10-10 in Modern Biology © 2006

Notice the direction of the synthesis Notice the direction of the synthesis

Steps of DNA Replication (Semi-Conservative

Replication)

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 SynthesisIII. Protein Synthesis

Ribonucleic acid, RNA, plays a role in protein synthesis.

Central ConceptDNA RNA protein

Ribonucleic acid, RNA, plays a role in protein synthesis.

Central ConceptDNA RNA protein

A. RNA Structure & Function

A. RNA Structure & Function

Differences in RNA than in DNASugar ribose instead of deoxyriboseNitrogenous base uracil instead

thymineSingle stranded instead of double

strandedShorter than DNA

Differences in RNA than in DNASugar ribose instead of deoxyriboseNitrogenous base uracil instead

thymineSingle stranded instead of double

strandedShorter than DNA

Types of RNATypes 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. TranscriptionB. 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 12-14 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 12-14 of Prentice Hall Biology

RNA EditingRNA 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 CodeC. 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 12-17Figure 12-17

D. TranslationD. 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 Translation

Figure 12-18

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 12-18

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 GenomeE. 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.

DNADNA

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 NotesEnd of Chapter 10 Notes