Unit 3: Genetics Part 1: Genetic Informaiton Book chapters 12 &13

Learning Goals Describe the overall structure of the DNA molecule Summarize the events of DNA replication Describe how RNA differs from DNA Name 3 main types of RNA Describe the events of transcription and translation Explain the relationship between genes and proteins Explain the 2 types of mutations

The Components of DNA DNA = DeoxyriboNucleic Acid DNA is a nucleic acid made up of nucleotides joined into long strands of chains by covalent bonds

Nucleotides Nucleotides are the building blocks of nucleic acids, like DNA Nucleotides have 3 basic parts: Sugar (Deoxyribose) Phosphate Group Nitrogen Base When nucleotides are bonded together, they form the ladder of DNA

Nitrogen Bases There are 4 different nitrogen bases: Adenine Thymine Cytosine Guanine They are identified by the first letter: A, T, C, G The bases pair up in a strand of DNA: A & T, C & G—this is base pairing The number of A in a strand of DNA will equal the number of T, and the number of G will equal the number of C

DNA Replication Before a cell divides, the DNA must be copied exactly Replication is the process of copying DNA Each original strand of DNA acts as a template to make the new strand. If the original strand is C A T, what is the new strand?

The Replication Process During replication, the DNA separates into 2 individual strands and then produces 2 new complementary strands following the base pairing rule

The Replication Process 1. The strand of DNA unwinds (now it looks like a ladder). 2. DNA helicase unzips the 2 strands by breaking the hydrogen bonds between the bases. The point at which the 2 strands split is called the replication fork

The Replication Process 3. DNA polymerase adds free floating nucleotides to the separated DNA strands. This creates the complementary strand 4. Two new strands of DNA are produced.

DNA Replication Half of the original strand of DNA is used as a template for the new DNA

RNA The discovery of DNA was not enough to answer the question of how a gene works The answer cam from the discovery of RNA (ribonucleic acid) RNA is also a long chain of nucleotides bonded together

RNA There are 3 important differences between DNA and RNA: The sugar in RNA is ribose instead of deoxyribose RNA is generally single stranded not double stranded RNA contains uracil instead of thymine

Types of RNA There are 3 kinds of RNA: Messenger RNA (mRNA) – carry copies of instructions for assembling amino acids into proteins Ribosomal RNA (rRNA) – assemble proteins in ribosomes Transfer RNA (tRNA) – transfers amino acids to the ribosome

Transcription In transcription, segments of DNA serve as templates to produce complementary RNA molecules

TRANSCRIPTION In transcription, the base sequences of the RNA complement the base sequences of the template DNA RNA is produced in the nucleus then moves out to the cytoplasm to help build proteins

RNA POLYMERASE & STEPS OF TRANSCRIPTION RNA polymerase is very similar to DNA polymerase RNA polymerase binds to DNA (at a promoter site) and separates the strands. RNA polymerase uses one strand of DNA as a template to create a complementary strand of RNA

Translation The decoding of an mRNA message into a protein is known as translation After transcription, mRNA leaves the nucleus to travel to a ribosome The ribosome reads the mRNA to know which amino acid is needed The amino acids are carried by a tRNA

Translation RNA contains 4 different bases: Adenine, Uracil, Cytosine, Guanine We call this language the genetic code The genetic code is read three “letters” at a time Each 3 letter “word” in mRNA is known as a codon

Translation How many codons are in this sequence? A G U U G A C C C A U G A U G A G C

Translation Most amino acids can be specified by more than one codon There are codons that signal both the start and stop of translation AUG is the only start codon UAA, UAG, and UGA are the three stop codons

Translation How many codons are in this sequence? A G U U G A C C C A U G A U G A G C