DNA James Watson L and Francis Crick R

DNA

James Watson (L) and Francis Crick (R), and the model they built of the structure of DNA

Structure of DNA – A Double Helix Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Go to Section:

Section 12 -2 Chromosome Nucleosome DNA double helix Coils Supercoils Histones Go to Section:

X-ray diffraction photograph of the DNA double helix

The structure of DNA and RNA Genetic material of living organisms is either DNA or RNA. • DNA – Deoxyribonucleic acid • RNA – Ribonucleic acid • Genes are lengths of DNA that code for particular proteins. • Remember that proteins are made of Amino Acids

• DNA is an ideal genetic material because – Can store information – Replicate – Undergo changes (variation or mutations)

DNA and RNA are polynucleotides • Both DNA and RNA are polynucleotides. • They are made up of smaller molecules called nucleotides. Nucleotide • DNA is made of two polynucleotide strands: Nucleotide Nucleotide Nucleotide • RNA is made of a single polynucleotide strand: Nucleotide Nucleotide

Structure of a nucleotide Composed of 3 parts 1. Pentose Sugar 2. Phosphate Group 3. Nitrogenous Base

Pentose Sugar A nucleotide is made of 3 components: • A Pentose sugar • This is a 5 carbon sugar • The sugar in DNA is deoxyribose. • The sugar in RNA is ribose.

Structure of a nucleotide Composed of 3 parts 1. Pentose Sugar 2. Phosphate Group 3. Nitrogenous Base

Structure of a nucleotide Composed of 3 parts 1. Pentose Sugar 2. Phosphate Group 3. Nitrogenous Base

Nitrogenous Base • A Nitogenous base • In DNA the four bases are: – – Thymine Adenine Cytosine Guanine • In RNA the four bases are: – – Uracil Adenine Cytosine Guanine P Nit Base Sugar

Base pairing • The Nitrogenous Bases pair up with other bases. For example the bases of one strand of DNA base pair with the bases on the opposite strand of the DNA.

Complementary base pairing Adenine Guanine Thymine Cytosine In RNA the following substitution Adenine Uracil Guanine Cytosine

The Rule: • Adenine always base pairs with Thymine (or Uracil if RNA) • Cytosine always base pairs with Guanine. • This is beacuse there is exactly enough room for one purine and one pyramide base between the two polynucleotide strands of DNA.

Structure of DNA Molecules

Replication

Section 12 -2 DNA Replication New strand Original strand DNA polymerase Growth Replication fork Nitrogenous bases Replication fork New strand Go to Section: Original strand

Replication of DNA and Chromosomes • Speed of DNA replication: 3, 000 nucleotides/min in human 30, 000 nucleotides/min in E. coli • Accuracy of DNA replication: Very precise (1 error/1, 000, 000 nt)

DNA Replication Step 1 Unwinding 1. The DNA must be unwound and bonds between the bases broken so that the two strands become separated. . 2. An enzyme helicase unzips and separates the two strands.

DNA Replication Step 2 Complimentary Base Pairing 1 Each strand serves as a template for the synthesis of a new strand. 2 DNA polymerase adds nucleotides to match to the nucleotide present on the template strand. A is paired with T and G with C.

DNA Main Ideas • DNA is coded information • Contains four kinds of bases (represented by A, G, C, and T). • Is replicated by unwinding and adding complimentary bases.

A replicating Drosophila chromosome

1. Which type of compound is found in every DNA molecule? (1. ) starch (2. ) nitrogenous base (3. ) lipid (4. ) amino acid 2. In a DNA molecule, a base pair could normally be composed of (1. ) adeninethymine (2. ) adenine-uracil (3. ) thymine-guanine (4. ) adenine-guanine 3. The deoxyribose part in the name deoxyribonucleic acid refers to the (1. ) rungs of the sugar ladder (2. ) bonds that hold the two strands together (3. ) sugar component of DNA (4. ) type of helical arrangement 4. A nucleotide of DNA could contain (1. ) adenine, ribose, and phosphate (2. ) nitrogenous base, phosphate, and glucose (3. ) phosphate, deoxyribose, and thymine (4. ) uracil, deoxyribose and phosphate 5. A molecular group consisting of a sugar molecule, a phosphate group, and a nitrogen base is a (1. ) nucleoprotein (2. ) amino acid (3. ) nucleic acid (4. ) nucleotide

6. Which statement concerning nucleic acids is FALSE? (1. ) DNA is a single stranded molecule. (2. ) DNA forms a twisted helix. (3. ) RNA contains ribose sugar. (4. ) RNA may contain uracil. 7. A nucleotide would least likely contain the element (1. ) carbon (2. ) nitrogen (3. ) phosphorus (4. ) sulfur 8. Which nitrogenous bases is NOT found in DNA? (1. ) thymine (2. ) uracil (3. ) adenine (4. ) guanine (5. ) cytosine 9. During the replication of the DNA molecule, bonds are broken between the (1. ) nitrogenous bases (2. ) phosphate groups (3. ) pentose sugars (4. ) sugars and phosphates 10. After the replication of the DNA molecule is completed, each of the two daughter cells is usually composed of (1. ) fragments from both strands of the parent DNA molecule (2. ) one nucleotide strand exactly like the parent nucleotide strands (3. ) nucleotides slightly different from the parent DNA molecule (4. ) nucleotides like the parent DNA molecule except that thymine is substituted for uracil

11. In nucleotides, the letters A, G, C, and T represent (1. ) phosphate groups (2. ) nitrogenous bases (3. ) deoxyribose sugars (4. ) ribose sugars 12. In a portion of a gene, the nitrogenous base sequence is T-C-G-A-A-T. Which nitrogenous base sequence would normally be found bonded to this section of the gene? (1. ) A-C-G-T-A-A (2. ) A-G-C-T-T-A (3. ) A-C-G-U-U-A (4. ) U-G-C-A-A-U 13. How would the complementary strand of DNA appear if the original strand of DNA contained the bases T-A-G-C in that order? (1. ) U-A-C-G (2. ) G-C-A-T (3. ) T-A-C-G (4. ) A-T-C-G

Protein Synthesis How do we get from To

Section 12 -3 Concept Map RNA can be Messenger RNA also called which functions to m. RNA Go to Section: Ribosomal RNA Carry instructions also called which functions to r. RNA Combine with proteins from to to make up DNA Ribosomes Transfer RNA also called which functions to t. RNA Bring amino acids to ribosome

Protein Synthesis Transcription The genetic code is transcribed to form a compliment m. RNA strand Translation The modified genetic code is transcribed into specific proteins

Function of DNA • DNA provides genetic code needed by cells to produce proteins. • Proteins make structures and form enzymes which control cellular functions and traits.

DNA vs RNA DNA • Deoxyribose • Thymine • Double chain RNA • Ribose • Uracil is substituted for Thymine A-U, C-G • Single chain

Types of RNA m. RNA – Messenger RNA t. RNA – Transfer RNA r. RNA – ribosomal RNA

Section 12 -3 Concept Map RNA can be Messenger RNA also called which functions to m. RNA Go to Section: Ribosomal RNA Carry instructions also called which functions to r. RNA Combine with proteins from to to make up DNA Ribosomes Transfer RNA also called which functions to t. RNA Bring amino acids to ribosome

Types of RNA m. RNA Carries DNA message from DNA in nucleus to sites of protein synthesis in the cytoplasm on ribosomes.

Types of RNA m. RNA Carries DNA message from DNA in nucleus to sites of protein synthesis in the cytoplasm on ribosomes. t. RNA • brings specific amino acid to a specific place on m. RNA • 3 -base code (triplet) is an “anticodon” Protein molecule Attached amino acid that is carried from cytoplasm to ribosomes

Types of RNA m. RNA Carries DNA message from DNA in nucleus to sites of protein synthesis in the cytoplasm on ribosomes . t. RNA brings specific amino acid to a specific place on m. RNA r. RNA holds m. RNA and t. RNAs in place to form chains of peptides

Steps for Protein Synthesis Transcription steps 1 -3 Translation steps 4 -6

DNA Transcription • DNA must be copied to messenger RNA (m. RNA) • m. RNA goes from nucleus to the ribosomes in cytoplasm • m. RNA complements known as codons – Only 3 nucleotide “letters” long • Remember RNA has uracil (U) instead of thymine (T)!

Section 12 -3 Transcription Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNA polymerase RNA Go to Section: DNA

Steps for Protein Synthesis 1. DNA in nucleus unzips and provides template for m. RNA.

Transcription Step 1 making a m. RNA copy of DNA • The part of the DNA molecule (the gene) that the cell wants the information from to make a protein unwinds to expose the bases. • Free m. RNA nucleotides in the nucleus base pair with one strand of the unwound DNA molecule.

Steps for Protein Synthesis 1. DNA in nucleus unzips and provides template for m. RNA. 2. Transcription: DNA is transcribed to form a compliment m. RNA strand which leaves the nucleus

Transcription Step 2 • The m. RNA copy is made with the help of RNA polymerase. This enzyme joins up the m. RNA nucleotides to make a m. RNA strand. • This m. RNA strand is a complementary copy of the DNA (gene) • The m. RNA molecule leaves the nucleus via a nuclear pore into the cytoplasm

Steps for Protein Synthesis 1. DNA in nucleus unzips and provides template for m. RNA. 2. Transcription: DNA is transcribed to form a compliment m. RNA strand which leaves the nucleus 3. m. RNA binds to a ribosome in the cytoplasm.

Animal Cell Nucleolus Nucleus Ribosome (attached) Nuclear envelope Ribosome (free) Cell Membrane Mitochondrian Smooth endoplasmic reticulum Rough endoplasmic reticulum Centrioles Golgi apparatus Animal Cell

Transcription Reminders • The template strand is the DNA strand being copied • The m. RNA strand is the same as the DNA strand except Us have replaced Ts

Protein Translation • Modified genetic code is “translated” into proteins • Codon code is specific, but redundant! – 20 amino acids – 64 triplet (codon) combinations

Translation Section 12 -3 Nucleus Messenger RNA is transcribed in the nucleus. Phenylalanine t. RNA The m. RNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the m. RNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the t. RNA that binds methionine. The ribosome also binds the next codon and its anticodon. Ribosome Go to Section: m. RNA Transfer RNA Methionine m. RNA Lysine Start codon

Translation (continued) Section 12 -3 The Polypeptide “Assembly Line” The ribosome joins the two amino acids— methionine and phenylalanine—and breaks the bond between methionine and its t. RNA. The t. RNA floats away, allowing the ribosome to bind to another t. RNA. The ribosome moves along the m. RNA, binding new t. RNA molecules and amino acids. Lysine Growing polypeptide chain Ribosome t. RNA m. RNA Completing the Polypeptide m. RNA Go to Section: Ribosome Translation direction The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

Translation Step 4. For each codon on the m. RNA, a specific t. RNA, with its anticodon, is brought in with an amino acid bound to it.

t. RNA structure • • 3 -base code (triplet) is an “anticodon” ONLY THREE NUCLEOTIDES LONG Protein molecule Attached amino acid that is carried from cytoplasm to ribosomes

t. RNA in cytoplasm has a codon attached to an amino acid

Translation Step 4. For each codon on the m. RNA, a specific t. RNA, with its anticodon, is brought in with an amino acid bound to it. Step 5. Translation: As the ribosome reads each codon, new t. RNA molecules are brought it to form a polypeptide. (assembly line)

Translation m. RNA to Polypeptide

Translation Step 4. For each codon on the m. RNA, a specific t. RNA, with its anticodon, is brought in with an amino acid bound to it. Step 5. Translation: As the ribosome reads each codon, new t. RNA molecules are brought it to form a polypeptide. Step 6. The chain becomes a polypeptide chain, which can fold in specific ways to become proteins. Proteins become structures and enzymes, which control cellular functions and traits.

The Genetic Code Go to Section: