DNA, RNA, and Protein Synthesis

Chapter 10

DISCOVERY OF DNASection 1

Griffith’s Experiments

• Fredrick Griffith studied bacteria that cause pneumonia– Some strains, or types, were harmful and

caused pneumonia in mammals (smooth)– Other strains were harmless and did not

cause pneumonia (rough)

Griffith’s Experiments

• Used the two strains of bacteria in four experiments

• Discovered that genetic material can be transferred from one cell to another and change those cells

• He called this transformation

Griffith’s Experiments

Avery’s Experiments

• Oswald Avery wanted to find out what factor caused the transformation in Griffith’s experiments

• Discovered that the factor was DNA

Hershey-Chase Experiment

• Experimented with bacteriophages – viruses that infect bacteria

• Confirmed that DNA is the hereditary molecule

Hershey-Chase Experiment

DNA STRUCTURESection 2

DNA Double Helix

• Structure of DNA discovered in 1953 by James Watson and Francis Crick

• Used Maurice Wilkins and Rosalind Franklin’s x-ray picture of DNA to help

DNA Nucleotides

• Made of two long strands of nucleotides– Each nucleotide contains three parts

• Five-carbon sugar (deoxyribose)• Phosphate group• Nitrogenous base

DNA Nucleotides

Bonds Hold DNA Together

• Structure is similar to a spiral staircase– Alternating sugar and

phosphate molecules = side handrails of the staircase

– Base pairs = steps of the staircase

Nitrogenous Bases

• Four kinds of bases– Adenine– Guanine– Thymine – Cytosine

Complementary Bases

• Base-pairing rules: • cytosine always pairs with guanine• adenine always pairs with thymine

Complementary Bases

• What is the complementary sequence of bases for the following strand of DNA?

• ACCTGTGAGAC• TGGACACTCTG

DNA REPLICATIONSection 3

DNA Replication

• DNA replication is the process by which DNA is copied in a cell before a cell divides

Steps of DNA Replication

1. Enzymes called helicases separate the DNA strands

Steps of DNA Replication

2. Enzymes called DNA polymerases add complementary nucleotides to each of the original strands

Steps of DNA Replication

3. DNA polymerases finish replicating the DNA and fall off– Result is two separate

and identical DNA molecules

DNA Errors in Replication

• DNA replication is usually very accurate– Only about one error occurs for every billion

nucleotides• When mistakes occur, a change in the

nucleotide sequence results in a mutation

PROTEIN SYNTHESISSection 4

Flow of Genetic Information

• DNA RNA protein

RNA Structure and Function

• RNA is very similar to DNA – long strand of nucleotides

RNA Structure and Function

• RNA is different from DNA in the following ways:– Contains the sugar ribose instead of

deoxyribose– Contains uracil instead of thymine– Single-stranded– Much shorter than DNA

Types of RNA

• There are three major types of RNA that each play a different role in protein synthesis

Types of RNA

• Ribosomal RNA (rRNA) – makes up part of the ribosome

Types of RNA

• Messenger RNA (mRNA) – carries the message from DNA in the nucleus to the ribosomes in the cytoplasm

Types of RNA

• Transfer RNA (tRNA) – transfers amino acids to the ribosome to make a protein

The Genetic Code

• The genetic code is the rules for how a sequence of bases codes for a particular amino acid

• Each group of three nucleotides is called a codon and codes for an amino acid

The Genetic Code

Transcription

• Instructions for a gene coded in DNA are rewritten into an RNA molecule

Translation

• Translation = the making of a protein

Steps of Translation

1. mRNA is fed through a ribosome three bases at a time

Steps of Translation

2. Molecules of tRNA translate the mRNA code by picking up a specific amino acid from the cytoplasm

Steps of Translation

3. In the ribosome, bases on the tRNA match with bases on the mRNA like pieces of a puzzle

Steps of Translation

4. tRNA releases their amino acids and they become linked in a chain