DNA and RNA Chapter 12

Genetic facts in 1900: Both female and male organisms have identical chromosomes except for one pair. Genes are located on chromosomes All organisms have two types of chromosomes: Sex chromosomes Autosomes

Chargaff’s rules The relative amounts of adenine and thymine are the same in DNA The relative amounts of cytosine and guanine are the same. Named after Erwin Chargaff

Rosalind Franklin Used X-Ray diffraction to get information about the structure of DNA:

Structure of DNA Discovered in 1953 by two scientists: James Watson (USA) Francis Crick (GBR) Known as the double-helix model.

WARM UP Write the complementary sequence to the following DNA sequence: The first three have been written for you. (Chargaff’s Rule) T A T T G C A G A T A A C T G A T A Write the complementary sequence to the following RNA sequence: The first three have been written for you. G A T T G C A G A T A A C T G C U A

Homework Write definitions for: DNA replication DNA helicase replication fork DNA polymerase

The double-helix A twisted ladder with two long chains of alternating phosphates and sugars. The nitrogenous bases act as the “rungs” joining the two strands. DNA is called the blueprint of life

How long is the DNA molecule?

Chromosomes & DNA replication The nucleus of one human cell contains approximately 1 meter of DNA. Histones = DNA tightly wrapped around a protein Nucleosome:

Chromosome structure:

DNA replication Must occur before a cell divides. Each new cell needs a copy of the information in order to grow.

DNA replication. Why needed? Before DNA strand can be replicated or copied it must be “unzipped” Helicase (enzyme that unzips) DNA Polymerase Starts at many different points. Why?

Completing the replication After the DNA molecule comes apart, bases of free nucleotides in the nucleus join their complimentary bases.

Proteins carry out the process of replication. DNA serves only as a template. Enzymes and other proteins do the actual work of replication. Enzymes unzip the double helix. Free-floating nucleotides form hydrogen bonds with the template strand. nucleotide The DNA molecule unzips in both directions.

DNA polymerase enzymes bond the nucleotides together to form the double helix. Polymerase enzymes form covalent bonds between nucleotides in the new strand. DNA polymerase new strand nucleotide

DNA replication is semiconservative. Two new molecules of DNA are formed, each with an original strand and a newly formed strand. DNA replication is semiconservative. original strand new strand Two molecules of DNA

Replication is fast and accurate. DNA replication starts at many points in eukaryotic chromosomes. There are many origins of replication in eukaryotic chromosomes. DNA polymerases can find and correct errors.

Complete the complimentary base pairings

Review A twisted ladder with two long chains of alternating phosphates and sugars. The nitrogenous bases act as the “rungs” joining the two strands. DNA is called the blueprint of life

Before DNA strand can be replicated or copied it must be “unzipped” Helicase (enzyme that unzips)

Completing the replication After the DNA molecule comes apart, bases of free nucleotides in the nucleus join their complimentary bases by DNA Polymerase

DNA MODELS 15mins

Due Dates Genetics Quiz - Unit 2 test – Nov 17th/18th DNA Projects – Nov 28th

PROTEIN SYNTHESIS

Pop Quiz 20 mins

RNA Very similar to DNA. Exceptions: Ribose is the 5-carbon sugar Uracil replaces thymine Single-stranded

mRNA (messenger) Copies genetic code of DNA by matching bases. Occurs in the nucleus. DNA changing to RNA

TRANSCRIPTION DNA is copied into mRNA with the aid of RNA polymerase. The RNA polymerase will bind to promoters that act as signals in the DNA sequence to make RNA.

Transcription continued:

Exons and Introns EXONS A segment of DNA in eukaryotic organisms that codes for a specific amino acid INTRONS A segment of DNA that does NOT code for an amino acid.

Confusing genetic terms: Polypeptide = a chain of amino acids. Protein = a complex structure composed of polypeptides Amino acids = smallest structural unit of a polypeptide. Gene = a distinct unit of material found on a chromosome

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

Codons A three letter “word” that specifies an amino acid.

Genetic code:

Practice

tRNA (transfer) approx. 80 nucleotides in length. Cross-like shape At one end an amino acid is attached At the other end there is an anticodon Acts like a truck

Polypeptide assembly Translation = reading or “translating” the RNA code to form a chain of amino acids. Known as protein synthesis Occurs in the cytoplasm. (p.304)

Mutations The source of variation in a genetic sequence. Can be either gene or chromosomal mutations. Point mutations = a change in a single nucleotide in a sequence of DNA.

Frameshift Mutation Inserting an extra nucleotide which, in turn, shifts the entire sequence one way or the other.

Chromosomal mutations Involves a change in the number or structure of the chromosomes. Deletion : when a piece of a chromosome breaks off and is lost. Duplication : when a segment of a chromosome is repeated Inversion : when a segment of a chromosome is reversed.

More chromosomal mutations Translocation : when part of a chromosome breaks off and is attached to a non-homologous chromosome.

Control of gene expression Genes are often like light switches that can be turned off and on. Operon = occur in prokaryotes. (bacteria) different genes that work together to activate gene functions

Factors: Overall gene control is more difficult for eukaryotes because functional genes may be on different chromosomes. Environmental such as chemicals and temperature.