Download DNA: The Molecule Of Life

DNA: The Molecule Of Life
Introductory Concepts
-One unique set of DNA in an organism is termed its genome (link to fig 1-3)
-DNA is the main component of chromosomes
-Humans are diploid organisms, with each somatic cell containing 46 chromosomes.
What Is DNA Made Of?
-DNA stands for deoxyribonucleic acid
-DNA is made up of three basic chemical components:
Phosphate.
Deoxyribose (a sugar).
Two Pyrimidines Cytosine and Thymine.
Two Purines Guanine and Adenine.
Important experiments relating to DNA
-Avery et al. discovered that DNA was the transforming principle in bacteria in 1944
-Hershey and Chase showed that DNA is the genetic material in 1952
-James Watson and Francis crick elucidated the structure of DNA in 1953.
The Structure of DNA
-Is composed of two strands in shape of a double helix.
-The strands are arranged in an anti-parallel fashion.
-The backbone of DNA is composed of a repeating phosphate deoxyribose polymer
- Bases are bonded to the 1' carbon of each molecule of deoxyribose
-The strands are held together by hydrogen bonds
Terminology
-Nucleoside- A base bonded to a sugar
-Nucleotide- A nucleoside bonded to a phosphate group
-Nucleotides form phosphodiester bonds in the 5' ---> 3' direction to make a molecule of DNA
What is a gene?
-a gene is a region of the DNA molecule which is made up of:
Regulatory region
Coding region (exons)
Non-coding region (introns)
Transcription termination sequence
The Structure of genes
The Regulatory region
-All genes have a region which is not transcribed and acts to regulate transcription, termed the regulatory region
Introns and exons
-Introns - regions of a gene which are transcribed but removed before translation
-Exon - the coding region of DNA which is translated
Structure Reflects Function
-Three requirements for heriditary material:
Replication
Information content
Periodic change
Structure of Chromosomes
-One way of viewing a cell's set of chromosomes is using a karyotype
-The region to which the spindle fibres attach during cell division is called the centromere
-Chromosomes can be classified as telocentric, acrocentric, or metacentric depending on the position of the centromere
Histone Proteins
-An animation explaing the packaging of DNA into chromosomes
-The material that makes up chromosomes is called chromatin
-complexes of DNA coiled around histones are called nucleosomes and look like a "beaded necklace"
-when the nucleosome is further coiled it is referred to as a solenoid
Gene Function
Recap:
-Structure and organization of DNA
-Structure determines function of DNA
What we are about to learn :
-Information exchange: DNA to protein
CENTRAL DOGMA OF GENETICS :
DNA
RNA
PROTEIN
Life processes
Think of the dogma like this:
-
DNA = blueprint
-
RNA carries instructions from the blueprint
-
PROTEINS = machines made from blueprint instructions
Look at Chapter overview before proceeding!
But what is RNA?
- Nucleic acid (like DNA)
-Single stranded (not like DNA)
-Ribose instead of deoxyribose (not like DNA)
-Adenine, Guanine, and Cytosine bases (like DNA)
-Uracil instead of Thymine (not like DNA)
Why do we need U and T?
-Can fold into many shapes
-Bring information from DNA to protein-making machinery
-Help build protein from DNA information
And what is protein?
-Large molecules made of chains of amino acids
-3 or 4 levels of structure
-The workhorses of the cell!!! Many functions
-structure determines function
So when the cell needs a job done it:
-Gets instructions from DNA
-Sends instructions through dispatcher (RNA)
-Machinery makes the right protein for the job
-Protein performs its function inside or outside of cell
Naming the Process!
Transcription = information from DNA passed to RNA
Translation = information from RNA used to make protein
Transcription
DNA
Translation
RNA
PROTEIN
Life processes
What are the instructions in DNA?
-How does DNA sequence (4 different nucleotides) = Protein sequence (20 different amino acids)?
-How is a gene sequence specific to one protein?
-How do protein-making machines read the instructions from DNA?
-The answers are found in THE GENETIC CODE!!!
What is the Genetic Code?
-Each gene contains a specific sequence of nucleotides
-Every three nucleotides (a codon) code for one amino acid
-Code is unambiguous
-Code is degenerate
-Code is (almost) universal
-organelles (mitochondria and chloroplast) have separate genomes
Why U’s instead of T’s in the genetic code?
- The code is based on the messenger RNA, not DNA
- Here’s how it works:
- DNA gene sequence is transcribed to form messenger RNA
-Complementary base pairing means RNA sequence = DNA sequence
-Remember both U and T bind to A!! Functionally the same!!!
- Protein-making machine (ribosome) reads messenger RNA sequence
-Carriers bring the amino acids to the ribosome by base-pairing to each codon
-Wobble hypothesis
-Special codons start and stop protein making (translation)
What we learn next
- Mutations
- Genotype vs phenotype
- Why peas are wrinkly or smooth!
Questions E-mail Lisa or Josh