Unit Objectives Describe the structure of DNA Compare and contrast DNA and RNA Understand the processes of transcription, translation and replication Identify types of mutations and causes of mutations
What is DNA? All living things contain proteins called enzymes which are needed for the functions of life. Within the structure of DNA is the information for life- the complete instructions for manufacturing all the proteins for an organism.
The Structure of DNA I DNA is a polymer made of repeating subunits called nucleotides. Nucleotides have 3 parts: a simple sugar, a phosphate group, and a nitrogen base.
The Structure of DNA II The simple sugar in DNA is called deoxyribose.
The Structure of DNA II The phosphate group is composed of one atom of phosphorous and four atoms of oxygen.
The Structure of DNA II A nitrogen base is a carbon ring structure that contains one or more atoms of nitrogen.
There are four possible nitrogen bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
DNA is made of two chains of nucleotides joined together by the nitrogen bases (determined by Watson and Crick).
The two strands twisted together make a shape called a double helix. The bases on one strand determine the bases on the other strand. They can be held together in this way because they are complimentary to each other.
The Structure of DNA III Adenine bonds with thymine and guanine bonds with cytosine. The amount of adenine is always equal to the amount of thymine while the amount of guanine is always equal to the amount of cytosine. These bonded bases are called complementary bases.
Nucleotide Sequences Differences in The closer the relationship between two organisms, the greater the similarity in their order of DNA nucleotides. Scientists use nucleotide sequences to determine evolutionary relationships among organisms, as well as criminal evidence.
Nucleotide Sequences The closer the relationship between two organisms, the greater the similarity in their order of DNA nucleotides. Scientists use nucleotide sequences to determine evolutionary relationships among organisms, as well as criminal evidence.
DNA Replication Copying of DNA in chromosomes Without DNA replication, new cells would have only half the DNA of their parents Species could not survive, reproduce, or grow
How DNA Replicates See pg 292, Copying DNA Inside Story After fertilization of egg, replication begins During replication, each strand serves as a pattern to make a new DNA molecule
How DNA Replicates Enzyme breaks the hydrogen bonds between nitrogen bases that hold the two strands together; unzips DNA Free floating nucleotides attach by base pairing to the individual single strands of DNA
Another enzyme bonds the nucleotide to the strand Continues until entire strand replicates Each new strand is a compliment of one of the original parent strand Result is the formation of two DNA molecules, identical to the original strand
From DNA to Proteins The sequence of nucleotides in DNA contains information for the production of proteins. –These proteins become everything from muscle tissue to walls of blood vessels and enzymes to assist in reactions of body (digestion, respiration)
RNA, like DNA is a nucleic acid RNA differs from DNA in 3 ways –RNA only has 1 strand, DNA has 2 –RNA has Ribose sugar, DNA has deoxyribose –RNA and DNA both contain Adenine, Cytosine, and Guanine. RNA has Uracil instead of Thymine
RNA receives instructions from DNA on how to assemble specific amino acids which go together to make proteins Three types of RNA –Messenger RNA (mRNA) Brings info. From the DNA in the nucleus to the cytoplasm of the cell –Ribosomal RNA (rRNA) contacts the mRNA and uses this info. To place amino acids in the correct order –Transfer RNA (tRNA) transports amino acids to the ribosome to be built into proteins
Transcription The making of RNA from a DNA molecule –See Fig. 11.6 –The nucleotide sequence is the blueprint to build proteins. –There are 20 different amino acids, and every 3 nitrogen bases (ex. AGU = Serine) codes for a different one. This is called a CODON –There are 64 possible codons in the genetic code Some code for “stop” or “start”, others for amino acids
Translation Turns mRNA into a sequence of amino acids which makes up a protein Takes place in the ribosomes mRNA and tRNA meet –Each tRNA carries anticodons, complimentary to codons on mRNA and picks up the correct amino acid and takes it to bond with the previous one. It releases one and goes to get the anticodon for another amino acid. –When a “stop” codon is reached, translation ends and the entire protein is released from the ribosome
Mutations: Mistakes in DNA Nuclear gamma radiation, etc. can alter the molecule if it comes in contact
Mutations: Mistakes in DNA A change in DNA sequence is called a mutation –Affect reproductive cells of an organism Can result in a new trait (+, but rare), a protein that does not correctly function, or an embryo that cannot survive
Types of Mutations UV radiation can change skin cells, which then grow and divide too rapidly causing skin cancer
Types of Mutations A POINT mutation is a change in a single base pair in DNA, which can change an entire protein.
Types of Mutations A FRAMESHIFT mutation adds or deletes a base and causes the entire code to shift up or down one
Chromosomal Mutations Most common in plants Parts of chromosomes can be lost during mitosis or meiosis Albino redwood Two headed kitten
Chromosomal Mutations Affect the distribution of genes to gametes, causing nondisjunction to occur (Down Syndrome trisomy) Few of these mutatations are passed on to next generation because people with these cannot mate
Chromosomal Mutations Most important types are: deletions, insertions, inversions, translocations –See figure 11.11
Causes of Mutations Just happen (spontaneous) Environmental factors –Caused by mutagens like UV, Nuclear and X-Ray radiation, chemicals, asbestos, cyanide, formaldehyde
Review Unit Objectives Describe the structure of DNA Compare and contrast DNA and RNA Understand the processes of transcription, translation and replication Identify types of mutations and causes of mutations