Chapter 10: Nucleic Acids and Protein Synthesis

DNA DNA (Deoxyribonucleic acid) –Stores and transmits genetic information –Double stranded molecule (looks like a spiral staircase or twisted rope ladder)

DNA Structure Double helical nature discovered in 1953 by Watson and Crick DNA is made of two strands of nucleotides that wrap around each other to form a double spiral or double helix

DNA Structure DNA is made of nucleotide sub-units 3 Parts of DNA nucleotide a. Deoxyribose (pentose sugar) b. Phosphate group c. Nitrogenous bases (A,T,G,C)

Nitrogenous Bases in DNA Adenine (A) pairs with Thymine (T) Guanine (G) pairs with Cytosine (C) Adenine and Guanine are purines- these are 2-ringed bases Thymine and Cytosine are pyrimidines- they are 1-ringed bases

Nitrogenous Bases The nitrogenous bases make up the “rungs” of the DNA ladder The bases are held together by Hydrogen bonds

DNA Replication Process of making a copy of the DNA Steps of DNA replication (Possible essay) 1.Helicase enzymes separate two strands of nucleotides (break the H-bonds that hold bases together) -the point at which the 2 strands of DNA separate is called the replication fork

2.Another enzyme (DNA polymerase) binds to separated strands and starts moving along originalDNA 3.DNA polymerase assembles a complementary strand from free nucleotides that are found in the nucleoplasm

4.Nucleotides are joined to new chain by covalent bonds b/t phosphate group and deoxyribose sugar and are joined to original DNA strand by H-bonds Ex: Original DNA sequence: ATTCCG DNA polymerase builds new strand that is complementary or TAAGGC

Replication Summary Replication does not begin on one end and move to other Instead, it starts and occurs simultaneously at different sites along DNA molecule (Ex: replication occurs at 6,000 different sites in fruit fly DNA) Allows for faster replication End result of replication- 2 identical DNA molecules, each consisting of one new strand and one from original DNA molecule

Accuracy of Replication Replication is very accurate (1 error per every 10,000 nucleotides) Errors in DNA are called mutations These changes in DNA sequence can have serious effects Enzymes proofread nucleotide sequence reducing error rate to 1 per 1 billion nucleotides

Other Agents that Damage DNA Chemicals Radiation (i.e. UV from sunlight) These can lead to mutations that could result in cancer

RNA RNA (Ribonucleic acid) Responsible for moving genetic info. from DNA in the nucleus to the site of protein synthesis in cytosol

RNA Structure Similar to DNA in that both are made of nucleotide sub-units Parts of an RNA nucleotide: a. Ribose (sugar) b. Phosphate group c. Nitrogenous base

Differences between DNA & RNA DNA 1. Sugar is Deoxyribose 2. Double-stranded molecule 3. Bases include: A, T, G, and C RNA 1.Sugar is Ribose 2.Single-stranded molecule 3.No T, replaced with Uracil (U)—Uracil is a pyrimidine

Types of RNA 1.Messenger RNA (mRNA) -single, uncoiled strand of RNA nucleotides *Carries the genetic info. from DNA in nucleus to cytosol of cell

RNA types (continued) 2.Transfer RNA (tRNA) -single chain of about 80 nucleotides -hairpin shape that binds to specific amino acids– helps form polypeptide chains

RNA types (continued) 3. Ribosomal RNA (rRNA) -RNA nucleotides in a globular form, joined by proteins makes up ribosomes -most abundant type of RNA Ribosomes are site of protein synthesis

Transcription -Process by which genetic information from DNA is copied to RNA (Possible Essay)

Steps of Transcription 1.RNA polymerase binds to specific region of DNA called a promoter (beginning of DNA strand that will be transcribed) -once the RNA polymerase bonds to the promoter, DNA will separate -one strand of DNA will be used for transcription

Transcription 2.RNA polymerase bonds to first DNA nucleotide of template strand -begins adding complementary RNA nucleotides to newly forming RNA molecule -follows complementary base pairing rules except Uracil pairs with Adenine

Transcription 3.RNA polymerase keeps adding nucleotides to RNA strand until it reaches a DNA region called the termination signal -once termination signal is reached, RNA polymerase releases DNA and newly formed RNA molecule

Transcription DNA strands will rejoin and the mRNA will leave the nucleus via a nuclear pore and head to the cytoplasm where it can direct protein synthesis All 3 types of RNA are made via transcription and all 3 will play a role in protein synthesis

Protein Synthesis Proteins are made of amino acid sub-units linked together by covalent peptide bonds 20 different amino acids Sequence of amino acids determines the type of protein that will be made Function of protein depends on structure

The Genetic Code Sets of 3 nucleotides in an mRNA strand that code for amino acid sequence in a protein Every 3 nucleotides in mRNA is called a codon Each codon codes for a specific amino acid

The Genetic Code There are 64 codons AUG is start codon (methionine) signals ribosome to start translating mRNA molecule 3 Stop codons: UAA UAG UGA

Translation Process of assembling proteins from information encoded in mRNA Happens on ribosomes Ribosomes attached to E.R. make membrane proteins and proteins that will be exported (i.e. insulin) Ribosomes in cytoplasm make proteins that are used within cell

Translation Shape of tRNA impacts function Anticodons of tRNA are complementary to mRNA codons

Translation Pairing of anticodons of tRNA with mRNA codons ensures that amino acids are added in the correct order

Steps of Translation 1.Ribosome attaches to start codon (AUG) on mRNA strand--Start codon pairs with anticodon (UAC) of a tRNA 2.Ribosome continues to move along mRNA and each codon pairs with a corresponding anticodon of tRNA

Translation 3. Ribosome keeps moving along mRNA strand until a stop codon is reached