The Structure and Function of DNA Chapter 10

I. DNA: Structure and Replication A. DNA and RNA Structure DNA=deoxyribonucleic acid RNA=ribonucleic acid

A. DNA and RNA Structure DNA and RNA are nucleic acids, made up of monomers called nucleotides Each nucleotide consists of 3 components: a nitrogenous base, a phosphate group, and a sugar

A. DNA and RNA Structure The sugar in DNA is deoxyribose The 4 bases in DNA are: Thymine (T), cytosine (C), adenine (A), and guanine (G)

A. DNA and RNA Structure The sugar in RNA is ribose The 4 bases in RNA are: Uracil (U), cytosine (C), adenine (A), and guanine (G)—the same as DNA, except RNA has uracil instead of thymine

B. Watson and Crick: The double helix Watson and Crick proposed that DNA molecules consisted of 2 individual polymers of linked nucleotides in the shape of a double helix –In each strand the phosphate of one nucleotide bonds to the sugar of the next –The bases protrude from the sugar-phosphate backbone

B. Watson and Crick: The double helix They also discovered that the nitrogenous bases pair together between strands (like the rung of a ladder) in a consistent pattern: –In DNA, A-T, and C-G –In RNA, A-U and C-G

B. Watson and Crick: The double helix There are no restrictions on the order of the nucleotides along the length of the DNA strand, however

DNA REPLICATION

C. DNA replication When a cell or whole organism reproduces, a complete set of genetic material must pass on from one generation to the next For this to occur, there must be a means of copying the instructions This is referred to as DNA replication

C. DNA replication Replication produces 2 identical double helices which are passed on to the daughter cells

DNA Replication Base pairing is the foundation for DNA replication Recall: adenine on one strand pairs to thymine on the other, and cytosine on one strand pairs with guanine on the other –ATG pairs with TAC Each strand has all the information to construct complementary strand

C. DNA replication DNA helicase pulls apart parental DNA double helix at the replication fork, forming a replication bubble (next slide) DNA polymerase moves along each separated parental DNA, matching bases on the strand with complementary free nucleotides as well as connects the nucleotide one with each other to form the new strand

C. DNA replication

After replication parent strand and daughter stand wind together Process is called semiconservative replication because result is a parental strand with a newly formed daughter strand

Checkpoint 1. Compare and contrast the chemical components of DNA and RNA. –Both are polymers of nucleotides. A nucleotide consists of sugar + a nitrogenous base + a phosphate group. In RNA, the sigar is ribose; in DNA it is deoxyribose. Both DNA and RNA have the bases A, G, and C; for a 4 th base, DNA has T and RNA has U

Checkpoint 2. Along one strand of a DNA double helix is a nucleotide sequence GGCATAGGT. What is the sequence of the other DNA strand? –CCGTATCCA

Checkpoint 3. How does complimentary base pairing make the replication of DNA possible? –When the 2 strands of the double helix separate, each serves as a template on which nucleotides can be arranged by specific base pairing into new complimentary strands

Checkpoint 4. What is the function of DNA polymerase in DNA replication? –The enzyme covalently connects nucleotides one at a time to on end of a growing daughter strand as the nucleotides line up along a template strand according to the base-pairing rules

The Flow of Genetic Information from DNA to RNA to Protein

II. The Flow of Genetic Information from DNA to RNA to Protein What exactly are the instructions carried by the DNA, and how are these instructions carried out?

This can be broken down into 2 stages: TRANSCRIPTION (the transfer of genetic info from DNA into an RNA molecule); and TRANSLATION (the transfer of the info in the RNA into a protein)

A. Transcription, a closer look: From DNA to RNA Transcription is the transfer of genetic information from DNA to RNA

A. Transcription: From DNA to RNA The DNA strands separate (as in replication) Only one strand serves as a template The RNA bases then take their appropriate place along the DNA template (A-U, C-G) The enzyme that links these nucleotides is called RNA polymerase

A. Transcription, a closer look: From DNA to RNA The RNA strand that is synthesized on the DNA template PEELS OFF the template, and then goes on for TRANSLATION

A. Transcription, a closer look: From DNA to RNA This RNA that is sent to the cytoplasm is called messenger RNA, or mRNA

A. Transcription, a closer look: From DNA to RNA 1. the RNA transcript has a tail and a cap added; this helps keep the strand from attack and helps ribosomes recognize the RNA

A. Transcription, a closer look: From DNA to RNA 2. Introns—those noncoding regions of the RNA—are removed

A. Transcription, a closer look: From DNA to RNA 3. Exons—those regions that code— are spliced together (called RNA splicing)

A. Transcription, a closer look: From DNA to RNA 4. Now the RNA, called mRNA, is sent to the cytoplasm, where the coding sequence on the mRNA is ready for translation

B. TRANSLATION: the transfer of the info in the RNA into a protein TRANSLATION is the 2 nd step of the process: the transfer of this information into a protein

B. TRANSLATION (the transfer of the info in the RNA into a protein) Remember that the RNA strand is made up of a series of nucleotides, for example, UUUAGACCG

B. TRANSLATION (the transfer of the info in the RNA into a protein) The nucleotides actually exist as TRIPLETS of bases/nucleotides called codons ex. AAA, AGG, ATC

B. TRANSLATION (the transfer of the info in the RNA into a protein) These codons each correspond to, or code for, a specific amino acid This is called the GENETIC CODE

B. TRANSLATION (the transfer of the info in the RNA into a protein) The GENETIC CODE is a set of rules relating nucleotide sequence/codons to amino acid sequence

B. TRANSLATION (the transfer of the info in the RNA into a protein) Almost all of the genetic code is shared by ALL organisms—from bacteria to plants to animals: it is UNIVERSAL

B. TRANSLATION (the transfer of the info in the RNA into a protein) In review: –One DNA codon (three nucleotides)  one RNA codon (three nucleotides)  one amino acid

Checkpoint 2. How many nucleotides are necessary to code for a polypeptide that is 100 amino acids long? –300

Checkpoint 3. An RNA molecule contains the nucleotide sequence CCAUUUACG. Using the Genetic Code, translate this sequence into corresponding amino acids –Pro-Phe-Thr

B. TRANSLATION (the transfer of the info in the RNA into a protein) There are 3 “players” in translation: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomes

B. TRANSLATION (the transfer of the info in the RNA into a protein) mRNA: –This is produced first by transcription and sent to the cytoplasm –Next, it needs to be translated by tRNA and ribosomes

B. TRANSLATION (the transfer of the info in the RNA into a protein) tRNA: –This RNA serves to translate, or convert, the 3 letter words (codons) of nucleic acids to the one-letter, amino acid words of proteins –tRNA molecules match amino acids to the appropriate codons to form the new polypeptides –The anticodon is a special triplet of bases at one end of the RNA. It recognizes a codon on the mRNA. At the other end of the tRNA is a site where an amino acid can attach

B. TRANSLATION (the transfer of the info in the RNA into a protein) Ribosomes –Ribosomes are the organelles that coordinate the functioning of the mRNA and tRNA and actually make polypeptides –The ribosome connects the amino acids to the growing polypeptide

II. Viruses: Genes in Packages A virus is a bit of nucleic acid with a protein coat They can only survive by infecting a living cell with genetic material, and therefore making more viruses

A. Bacteriophages Bacteriophages are viruses that infect bacteria A bacteriophage latches onto a bacteria cell and inserts its DNA into the bacteria Then the bacteria go to reproduce, all with this viral DNA inside

B. Plant viruses Viruses that infect plant cells can stunt plant growth and diminish crop yields Generally, a plant must be damaged for a virus to enter

C. Animal viruses Viruses are common in animals Many viruses have RNA instead of DNA as their genetic material RNA viruses include the common cold, measles, mumps, and polio DNA viruses include hepatitis, chicken pox, and herpes

D. HIV, the AIDS virus HIV is a retrovirus, an RNA virus that reproduces by means of a DNA molecule; that is, it synthesizes DNA on an RNA template