Chapter 10: DNA and RNA

DNA Deoxyribonucleic acid Structure of DNA Made up of four subunits called nucleotides Each nucleotide is made up of a sugar, a phosphate and a base

Four Bases Two Purines Two pyrimidines Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

DNA Double Helix DNA is made of two nucleotide strands that wrap around each other in the shape of a double helix.

DNA Structure Bonds Hold DNA Together Nucleotides along each DNA strand are linked by covalent bonds. Complementary nitrogenous bases are bonded by hydrogen bonds.

Chargaff Amount of adenine equals the amount of thymine and the amount of cytosine equals the amount of guanine A=T C=G

But what does DNA look like? Rosalind Franklin Working in Wilkin’s lab created x-ray pictures of DNA Wilkins shared this information with another pair of scientists without Franklin’s consent

Watson and Crick Watson and Crick discovered that DNA resembles a twisted ladder shape: double helix

DNA Structure Two side of the ladder are made up of alternating sugar and phosphate molecules The rungs of the ladder are pairs of bases (A with T, and G with C): Base pair rule Rungs are anti-parallel (5’->3’ and 3’ ->5’)

Drawing DNA Draw one side of the rung 5’ -> 3’ Start with the sugar Add the phosphate and the base to form your nucleotide Continue adding bases to the 3’ end Determine the matching base for next side When finishing each nucleotide, be sure to draw in the 3’ -> 5’ direction

Making copies: Replication DNA can “unzip” when it needs to replicate (helicase) Occurs prior to cell division so each new cell gets the correct information

Replication DNA molecule separates into two strands Complementary strands form on the template of each of the original sides of the DNA Each new DNA has one old and one new strand (semiconservative replication)

Replication enzymes Helicase Primase DNA polymerase Ligase Unwinds DNA Adds an RNA primer on unzipped DNA DNA polymerase Add new bases to the 3’ end of previous base Ligase Seals fragments after RNA primer removed

Steps of DNA Replication Replication begins with the separation of the DNA strands by helicases. Then, primase adds an RNA primer where replication will occur DNA polymerases form new strands by adding complementary nucleotides to each of the original strands. The new segments of DNA are sealed by ligase

See it in action: http://www.johnkyrk.com/DNAreplication.html http://www.dnareplication.info/images/dnareplication.jpg See it in action: http://www.johnkyrk.com/DNAreplication.html

DNA Replication

DNA Replication Each new DNA molecule is made of one strand of nucleotides from the original DNA molecule and one new strand. This is called semi-conservative replication.

Replication Forks Increase the Speed of Replication

Replication DNA polymerase can only add to a 3’ end Leading strand Runs 5’->3’ Lagging strand Runs 3’->5’ SO can’t add directly Have to replicate in fragments called Okazaki fragments Ligase bonds the fragments together

Single-strand binding protein Overall directions of replication DNA Replication Overview Origin of replication Leading strand Lagging strand Leading strand Lagging strand Single-strand binding protein Overall directions of replication Helicase Leading strand 5 DNA pol III 3 3 Primer Primase 5 Parental DNA 3 Figure 16.17 A summary of bacterial DNA replication DNA polymerase Lagging strand 5 DNA polymerase DNA ligase 4 3 5 3 2 1 3 5

Replication animation http://www.mcb.harvard.edu/Losick/images/TromboneFINALd.swf

Central Dogma Has its exceptions, but gives us a basic idea of how DNA does its job

RNA Single stranded nucleic acid Made up of nucleotides Sugar: Ribose Thymine instead of Uracil Shorter: length of one gene

RNA Structure and Function Types of RNA Cells have three major types of RNA: messenger RNA (mRNA) ribosomal RNA (rRNA) transfer RNA (tRNA)

Activity In pairs, create a chart that will fit in your foldable (no more than 1/8th size of construction paper) that compares and contrasts the different forms of RNA Be sure to include: Name Structure Function Picture

RNA Structure and Function mRNA carries the genetic “message” from the nucleus to the cytosol. rRNA is the major component of ribosomes. tRNA carries specific amino acids, helping to form polypeptides.

Making proteins Cells use a two step process to read each gene and produce the amino acid chain that becomes a protein. These processes are: Transcription Translation http://gslc.genetics.utah.edu/units/basics/transcribe/

Gene 2 Gene 1 Gene 3 DNA template strand mRNA Codon TRANSLATION Fig. 17-4 Gene 2 DNA molecule Gene 1 Gene 3 DNA template strand TRANSCRIPTION Figure 17.4 The triplet code mRNA Codon TRANSLATION Protein Amino acid

Transcription The process of building an RNA copy of a DNA sequence DNA is too big to leave the nucleus mRNA is a copy of the DNA sequence

mRNA Also known as messenger RNA Takes the code out into the cell for protein synthesis

Steps of Transcription Initiation RNA polymerase binds to a promoter (specific nucleotide sequence: TATA box) Elongation RNA polymerase adds free RNA nucleotides that are complementary to the DNA strand Termination RNA polymerase releases at a termination sequence

Steps of Transcription

Completed RNA transcript Promoter Transcription unit 5 3 3 5 DNA Start point RNA polymerase 1 Initiation 5 3 3 5 RNA transcript Template strand of DNA Unwound DNA 2 Elongation Rewound DNA 5 3 3 3 5 Figure 17.7 The stages of transcription: initiation, elongation, and termination 5 RNA transcript 3 Termination 5 3 3 5 5 3 Completed RNA transcript

Genetic Code The nearly universal genetic code identifies the specific amino acids coded for by each three-nucleotide mRNA codon.

Translation Steps of Translation During translation, amino acids are assembled from information encoded in mRNA. As the mRNA codons move through the ribosome, tRNAs add specific amino acids to the growing polypeptide chain. The process continues until a stop codon is reached and the newly made protein is released.

Ribosome Amino acids tRNA with amino acid attached Ribosome tRNA Polypeptide tRNA with amino acid attached Ribosome Trp Phe Gly Figure 17.13 Translation: the basic concept tRNA Anticodon 5 Codons 3 mRNA

Translation: Assembling Proteins

DNA Errors in Replication Changes in DNA are called mutations. DNA proofreading and repair prevent many replication errors. DNA Replication and Cancer Unrepaired mutations that affect genes that control cell division can cause diseases such as cancer.

The Human Genome The entire gene sequence of the human genome, the complete genetic content, is now known. To learn where and when human cells use each of the proteins coded for in the approximately 30,000 genes in the human genome will take much more analysis.