Chapter 8: DNA
Fredrick Griffith
• In 1928, ______was studying two forms or strain of a bacterial species: one strain was fatal to mice, while the other strain was harmless.
• When he injected heat-treated bacteria into mice, the mice remained ______.
• Heat kills the deadly strain of bacterium, making it harmless.
• When he injected mice with a mixture of the ______strain and the ______deadly strain, he expected the mice to survive.
• However, the mixture ______the mice. Some of the harmless bacteria had been “transformed”, becoming deadly.
DNA or Protein?????
• After Griffith’s experiment, scientists began to search for the “transforming factor”.
• Attention focused on two types of chemicals: protein and DNA.
• In 1952, biologists ______and ______provided more evidence to distinguish between the two possibilities.
• They conducted a series of experiments using viruses.
Virus
• A virus is package of ______wrapped in a ______.
• Unlike living things, viruses are not made of ______.
• A virus can only reproduce by ______a living cell with its genetic material.
• A virus that infects bacteria is called a ______.
• Phage consists of a protein coat that encloses the genetic material. When a phage infects a bacterium, it inserts its ______into the bacterium, while its coat remains outside.
Hershey and Chase’s Experiment
• In the first experiment, phages with radioactive-labeled ______, infected bacteria.
• In a second experiment, phages with radioactive-labeled ______, infected bacteria.
• In both experiments, bacteria were separated from the phage coats by blending.
• In the first experiment, most radioactivity was found in the ______, while in the second experiment most radioactivity was found in the ______.
• These experiments demonstrated that ______is the genetic material of phage and that protein ______transmit genetic information.
DNA Structure
• The heritable ______of an organism is stored in DNA.
• The DNA molecule is made up of two strands that are held together by ______.
• These strands are ______to each other but run in opposite directions, called ______.
• Each strand of DNA consists of a large number of ______.
DNA Structure
• Each nucleotide is made up of a ______(sugar), a ______group and a ______.
• There are 4 kinds of nitrogenous bases, ______(T), ______(C), ______(A), and ______(G).
• Bases Thymine (T) and Cytosine (C) are single-stranded structure called ______.
• Bases Adenine (A) and Guanine (G) are double-stranded structures called ______.
• In the double stranded DNA, ____ always pairs with ___ and ___ always pairs with ___. This is called complementary base pairing.
DNA Strands
• Nucleotides are joined to one another by ______that connect the sugar of one nucleotide to the phosphate group of the next.
• This repeating pattern of sugar-phosphate is called a ______.
• Knowing the main components of DNA, Watson and Crick tried to figure out how the elements fit together?
• One clue came from X-ray photographs of DNA taken by Rosalind Franklin. These photographs suggested that the structure of DNA was a ______.
DNA Replication: The process of copying the DNA molecule.
• This process can be divided into 3 major parts:
1. Binding of ______to existing DNA
2. ______the double helix
3. ______of a new matching strand for each existing strand
RNA: DNA:
______-stranded ______-stranded
Ribose Deoxyribose
______
Types of RNA:
1. mRNA - ______- carries information from DNA to the ribosome where the protein is made.
2. tRNA - ______- carries amino acids to mRNA at the ribosome to assembly the protein being made.
3. rRNA - ______- major structural component of the ribosome where protein synthesis occurs.
The Central Dogma:
DNA is maintained by ______, DNA is ______into RNA, RNA is ______into protein.
What are proteins?
• We are protein.
• Our hair, our nails, our skin, our blood, our enzymes and hormones are ______;
indeed, our bodies contain some ten thousand to fifty thousand kinds of protein.
Genetic Alphabets:
There are three alphabets involved in the entire process of protein synthesis
1) DNA - ______
2) RNA - ______
3) Protein - ______different ______
• Triplet Code - ______nucleotides code for one amino acid
1. Codon – a triplet in ______, pairs with triplet on a tRNA molecule carrying the correct amino acid.
2. Anticodon – a triplet in ______
The Genetic Code:
• Example #1: mRNA Codon = AUG àààà Amino Acid = ______
• Example #2: CUAGGCAACUUA àààà Amino Acid = ______
• Example #3: UUACGCCGUAAG àààà Amino Acid = ______
Transcription:
• Purpose: to synthesize ______from a ______template
• It starts when the enzyme RNA polymerase attaches to a specific region of the DNA.
• As a result, a single complementary strand of ______is made.
Editing the mRNA message:
• Transcribed mRNA must first be edited before it can leave the nucleus for the cytoplasm.
• The initial RNA transcripts have stretches of ______nucleotides that interrupt nucleotide sequences that actually code for amino acids.
Splicing:
• Splicing - ______are removed and ______are joined together.
• Intron - segment of mRNA which ______code for protein; therefore, it is removed.
• Exon - segment of mRNA which ______code for protein; therefore, it remains for expression in protein.
Translation:
• It is the final step on the way from DNA to protein.
• It is the synthesis of ______directed by a mRNA template.
• ______translates the three-letter codons of mRNA to the amino acids that make up proteins. This happens on ribosomes.
tRNA during Translation:
1. A tRNA molecule must become bound to the appropriate ______.
2. It has to recognize the appropriate ______in the mRNA.
3. During translation, the ______on tRNA recognizes a particular ______on mRNA by using base-pairing rules.
Ribosome:
• A ribosome has two subunits:
– Small subunit: binding site for mRNA
– Large subunit: consist of two binding sites for tRNA
• “P” site: holds the tRNA carrying the growing ______.
• “A” site: holds the tRNA carrying the next ______to be added to the chain.
Steps of Translation:
l First, the ribosome attaches at a specific site on the mRNA. This site is the start codon, ______.
l Next, amino acids are added one by one to the growing chain of amino acids.
l During translation, the ______moves down the mRNA, codon by codon, until translation is completed.
l This process continues until the ribosome reaches a stop codon: ______
Mutation
• A mutation is ______in the nucleotide sequence of DNA.
• Mutations can change the meaning of genes.
• Mutations can involve large regions of a chromosome or just a single nucleotide.
• Mutation can be divided into 2 general categories.
1. Base substitution: ______of one base or nucleotide with another.
· It results in a change that affects the function of a protein.
2. Base insertion or deletion: ______or ______nucleotides.
· It’s usually more disastrous than the effects of base substitutions.
What Causes Mutation?
• May occur when errors are made during ______.
• May occur when errors happen during chromosome ______in meiosis.
• Physical or chemical agents that called mutations are called ______.
• Most common physical mutagen is high-energy radiation. Ex: X-rays
• ______are the ultimate source of genetic diversity in the living world.