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Chapter 12 •DNA structure and replication •RNA •Transcription •Translation •Protein synthesis •Amino acids Discovery of the Genetic Material • After the rediscovery of Mendel’s work, scientist began to look for the molecule involved in inheritance. • For many years, scientists struggled to determine if DNA or protein was the source of genetic information. Copyright © McGraw-Hill Education Discovery of the Genetic Material Miescher • 1860’s • “nuclein” Griffith • First major experiment searching for the genetic material • Involved transformation between two forms of S. pneumoni Copyright © McGraw-Hill Education Chromosome Structure • To fit into a cell, DNA coils around a group of beadlike proteins • Group together into chromatin fibers • Supercoil to form a chromosome. Copyright © McGraw-Hill Education DNA: The Genetic Material Chromosome Structure • Eukaryotes – DNA in individual chromosomes • Nucleus • Prokaryotes – DNA in Cytoplasm Copyright © McGraw-Hill Education DNA: The Genetic Material DNA Structure James Watson (L) and Francis Crick (R), and the model they built of the structure of DNA. Copyright © McGraw-Hill Education DNA Structure Double helix • X-ray diffraction techniques indicated that DNA was a double helix, or a twisted ladder shape. • Formed by two strands of nucleotides twisted around each other. Copyright © McGraw-Hill Education 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. DNA and RNA are Polynucleotides •Both DNA and RNA are polynucleotides. •Poly = many Nucleotide are made up of smaller molecules called nucleotides. •DNA is made of two polynucleotide strands: •They Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide •RNA is Nucleotide made of a single polynucleotide strand: Nucleotide Nucleotide Nucleotide Nucleotide DNA Structure Nucleotides • Nucleotides are the subunits of nucleic acids, and consist of • 5-carbon sugar • Phosphate group • Nitrogenous base DNA Structure • Pentose Sugar – 5 carbon sugar – DNA – deoxyribose – RNA - ribose DNA Structure • Phosphate Group – Link the sugar of one nucleotide onto the phosphate of the next nucleotide to make a polynucleotide. DNA Structure A Nitrogenous base: • In DNA the • Thymine • Adenine • Cytosine • Guanine four bases are: • In RNA the • Uracil • Adenine • Cytosine • Guanine four bases are: AS Biology. Gnetic control of protein structure and function Four DNA bases •Four kinds of nitrogenous bases: •Purine bases •Pyrimidine bases DNA: Complimentary base pairing •Adenine pairs with Thymine A = T Bond Type = double •Cytosine pairs with Guanine C = G Bond Type = Triple DNA Structure • DNA often is compared to a twisted ladder. • Rails of the ladder are represented by the alternating deoxyribose and phosphate. • The pairs of bases (cytosine-guanine or thymineadenine) form the steps. DNA STRUCTURE VIDEO YUMMY GUMMY DNA DNA Replication (in nucleus) • Matching bases allows DNA to be easily copied Making new DNA •Replication •Copying DNA •DNA starts as a double-stranded molecule •matching bases (A:T, C:G) •then it unzips… DNA Replication •Strands bases “unzip” at the weak bonds between DNA Replication DNA bases in nucleus • Enzyme • DNA polymerase DNA polymerase • adds new bases Copying DNA Build daughter DNA strand use original parent strand as “template” add new matching bases synthesis enzyme = DNA polymerase DNA Polymerase New copies of DNA •Get 2 exact copies of DNA to split between new cells DNA polymerase DNA polymerase Copied & Paired Up Chromosomes centromere Comparing DNA Replication • Eukaryotes and Prokaryotes – Eukaryotic DNA unwinds in multiple areas as DNA is replicated. – In prokaryotes, the circular DNA strand is opened at one origin of replication. Copyright © McGraw-Hill Education 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/1,000,000,000 nt) AS Biology. Gnetic control of protein structure and function 3 Base your answer to the following question on the diagram below which represents a portion of a doublestranded DNA molecule and on your knowledge of biology. The base sequence of strand II is most likely: 1. C-A-C-T-G-G 3. G-T-G-U-C-C 2. G-G-T-C-A-C 4. G-T-G-A-C-C 4 Practice •On your paper, complete the missing DNA strand by adding the complementary bases. •A T C G T T G C C A T C •T A G C A A C G G T A G DNA, RNA & PROTEIN Chapter 12: Section 3 Central Dogma •Investigate how DNA served as a genetic code for the synthesis of proteins. •Geneticists accept that the basic mechanism for reading and expressing genes is from DNA to RNA to protein. •This is referred to as the central dogma of biology: •DNA codes for RNA, which guides the synthesis of proteins. Copyright © McGraw-Hill Education RNA differs from DNA 1. RNA has a sugar ribose DNA has a sugar deoxyribose 2. RNA contains uracil (U) DNA has thymine (T) 3. RNA molecule is single-stranded DNA is double-stranded Central Dogma Three Types of RNA • Messenger RNA (mRNA): long strands of RNA that are formed complementary to one strand of DNA; direct synthesis of a specific protein • Ribosomal RNA (rRNA): associates with proteins to form ribosomes in the cytoplasm • Transfer RNA (tRNA): smaller segments of RNA that transport amino acids to the ribosome Copyright © McGraw-Hill Education Central Dogma Transcription •First step synthesis of mRNA from DNA in a process called transcription. •RNA polymerase moves along the DNA strand in a 3’ to 5’ direction, synthesizing mRNA. Copyright © McGraw-Hill Education Practice •Make the complementary RNA strand for the single strand of DNA below: •A A T C A T C A C G T T •U U A G U A G U G C A A •Make the complementary RNA strand for the single strand of DNA below: •T A C C C G A G G T A G C C G C G T A T T •A U G G G C U C C A U C G G C G C A U A A Reading the genetic code •The genetic code is responsible for building all the proteins in the body using 20 different amino acids. •How many 3 letter words can you make from the letters A,T,G and C? •Answer: 64 The Code •Scientists hypothesized that the instructions from protein synthesis were encoded in DNA. •Experiments during the 1960s demonstrated that the DNA code was a three-base code. •The three-base code in DNA or mRNA is called a codon. Copyright © McGraw-Hill Education DNA, RNA, and Protein Codons •A three letter “word” that specifies an amino acid. A. Messenger RNA (mRNA) start codon mRNA A U G G G C U C C A U C G G C G C A U A A codon 1 protein codon 2 methionine glycine codon 3 serine codon 4 isoleucine codon 5 glycine codon 6 alanine codon 7 stop codon Primary structure of a protein aa1 aa2 aa3 peptide bonds aa4 aa5 aa6 The Code Translation • After synthesis, mRNA moves from the nucleus into the cytoplasm, where it connects to a ribosome. • The mRNA code is read and translated into a protein through a process called translation. Copyright © McGraw-Hill Education DNA, RNA, and Protein The Code Translation • tRNA molecules act as the interpreters of the mRNA codon sequence. • The tRNA is activated by an enzyme that attaches a specific amino acid to the end. • The middle of the folded tRNA contains an anticodon, a complementary sequence to the mRNA codon. Copyright © McGraw-Hill Education DNA, RNA, and Protein The Code The role of the ribosome • Ribosomes provide a site for protein synthesis. • When mRNA leaves the nucleus, the two ribosomal subunits come together to hold the mRNA in place for translation. • The ribosome structure has grooves that hold the mRNA and serve as tRNA sites for amino acid attachment. Copyright © McGraw-Hill Education From DNA to Protein DIFFERENCES DNA RNA • Deoxyribonucleic acid • Ribonucleic acid • Double strand • Single strand • G, C, A, T • G, C, A, U deoxyribose sugar • Inheritance of traits & enzyme production • ribose sugar • • protein synthesis SIMILARITIES NUCLEIC ACIDS C, G, A found inside the nucleus If the cell is a school… •The Nucleus is the school office •The Nucleolus is the principal’s office •The DNA is the principal •Ribosomes are the cafeteria ladies •mRNA is the email from the principal to the cafeteria lady Review/Explain: Types of Nucleic Acids What are the two types of nucleic acids? Ribonucleic Acid (RNA) • Single Stranded Deoxyribonucleic Acid (DNA) • Double Helix • (Twisted Ladder) DNA • Deoxyribose • Base Sugar Pairs A-T G-C • Phosphate • Most Importantly--• Contains the Code for ALL the Proteins in the Body RNA • • • • Ribonucleic Acid Sugar + Phosphate backbone Differs from DNA • Single Stranded • Ribose Sugar • Base Pairs A-U, G-C RNA assists DNA in manufacturing needed proteins Questions •Name one difference between DNA and RNA. •DNA – Double Helix, RNA – Single Stranded •DNA --- A-T, RNA ---A-U •DNA ---Deoxyribose Sugar, RNA--Ribose •What is a similarity of DNA and RNA? •G binds with C in both DNA and RNA •Both have sugar and phosphate backbone Gel Electrophoresis •use to separate DNA fragments • determine relationships • used in forensics Study the diagram on the left side of this slide. Which of the following DNA samples of individuals are most closely related? EXPLAIN. DNA sample 1 & 7 Crime Scene #1 Crime Scene #2 Crime Scene #3 Paternity Paternity #1 Dad 2 Paternity #2 WHO ARE THE PARENTS? WHO ARE THE PARENTS? Child 1 Child 2 Child 3 Child 4 Mom and Dad Mom Mom and Dad Neither