10.1 How genes work: DNA RNAprotein
1. Differentiate between phenotype and genotype
2. Explain how the information in DNA is transformed into something we can observe. Given a DNA
sequence, you will be able to write out what it is transcribed into as an mRNA and then, with a codon
table, write out the resulting amino acid sequence. As well, with examples you will be able to describe
how the presence of a translated protein could result in some observable characteristic (called a
Readings: Chapters 8: 197-205, 206-208
See animation here www.youtube.com/watch?v=6dMlde9akBk or another animation in the course vista wk10
Introductory Exercise to thinking like a geneticist:
Before class describe 3 things about yourself, such as eye colour, hairy toes, dimples, or the ability to touch
your knee with your chin without bending your legs, etc. Then consider whether you think these
characteristics are controlled by your genes or by the environment (outside influences) or both.
You have just been describing aspects of phenotype, the observable or detectable characteristics of an
Phenotype may be easily visible characteristics such as shape, form, colour, texture, size, or length. It could
also be a biochemical property such as the ability to digest lactose or the ability to metabolize alcohol or
regulate blood sugar through insulin. Phenotype could also be aspects of behaviour such as the ability of
animals to make specific mating calls, the ability of plants to turn their leaves towards light. Virtually every
aspect of an organism that you can describe, measure, or detect in some way is an example of its phenotype.
Often completely dependent on our genetic makeup
Majority of phenotype is also determined by both genetics and environment (example: skin color)
Genotype is an organism’s genetic makeup, presented as the DNA sequence for a gene (or genes), that affects
a particular phenotype (characteristic) of the organism.
Phenotype is controlled by both genotype (inherited characteristics) and the environment.
If we look around this room we will notice differences in hair colour phenotypes among individuals. If we
survey the class we will find some people who can digest milk sugar and some people who are lactose
intolerant, two different phenotypes.
The phenotypes of human eye colour and lactose intolerance are both controlled (almost) entirely by
genotype. There are differences in the DNA sequences between individuals, but how do the DNA sequence
differences manifest into the characteristics we see?
A gene is a specific sequence of DNA that codes for (with instruction to construct) a functional protein (only
a small percentage of of genomic DNA is actually coding sequence).
Difference between DNA chromosome and gene: Gene is a specific section of the DNA in the
Chromosome. DNA is a chemical composition of a long molecule which contains information and instructions;
it is the chemical component which carries instruction or information. When DNA condenses into a visible
form under a microscope it is a chromosome. Genes are positions on DNA molecules which contain
instructions to code for proteins. Chromosomes are a long string of DNA which condenses into a physical
structure. DNA (gene) RNA (mRNA) protein (mostly enzymes)
DNA and RNA are composed of nucleic acids/nucleotides held together in chains FYI:RNA nucleotides are
slightly different because they have an extra oxygen which DNA lacks (RNA = ribonucleic acid DNA =
deoxyribonucleic acid) See Fig 8.1 in your textbook (abbreviated below)
DNA must be transcribed to RNA
DNA in nucleus
Manufacturing of protein is in the cytoplasm
RNA – messenger RNA carries information from the DNA in the nucleus to the cytoplasm to help manufacture
4 nucleotides in DNA ACGT4 nucleotides in RNA ACGU
Proteins are composed of amino acids held together in chains
(20 types of amino acids)
represented like this
but looks more like this in reality
Proteins may serve as structures (e.g., microtubules, receptors on cell surfaces, keratin – the protein which
makes your hair)
Proteins may be involved in chemical reactions (e.g., enzymes). Enzymes are proteins that facilitate chemical
reactions. Often they transform one chemical molecule into another.
Proteins can be muscles (physical strength) or enzymes (biochemical reactions)
Must be folded into specific shape in order to function properly—this is done with amino acids
In all cases the shape of a protein is the key to its function. The shape of a protein is determined by the
specific sequence of amino acids that make up the protein molecule.
It occurs in the nucleus of eukaryotic cells (or in the cytoplasm
Things to remember: of prokaryotes, which do not have a nucleus);
DNA is double stranded and A=T, C=G
RNA is single stranded and A=U, C=GIt involves copying a segment of DNA (gene) into mRNA
RNA is synthesized by using one DNA strand as a guide (template)
T A C C A C T G strand
A A U G G U G A C T C C G A
G G A T T G
G G C T A
A T A A C
Non-template G A A T G G T G A G
strand U A A C
transcription start site termination site
1a. The transcription occurs when RNA polymerase (manufactures RNA in the nucleus of the cell) is able to
bind to the promoter in the regulatory region. Specific proteins can bind to this region to either inhibit or
activate RNA polymerase.
be regulated by proteins such as repressors or activators which bind to the promoter region.nto mRNA) can