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3.1 Protein Synthesis and Common DNA Lecture Notes
1.
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Common DNA
a. DNA is common in all organisms, regardless of species!
b. Inherited from parents (THINK MEIOSIS AND SEXUAL REPRODUCTION!)
i. ½ of DNA from each parent
c. Controls the development and maintenance of organisms
d. The Genetic Code
i. An organisms entire set of genetic instructions
ii. Also called a genome
e. Striking unity of DNA:
i. DNA is the universal genetic language common to all organisms
1. A-C-T-G are present in all organisms
2. Sequence is just slightly different in each.
3. This change in sequence determines organism!
Protein Synthesis
a. DNA contains all the information in the A-C-T-G to build proteins
b. Proteins
i. Run living organisms
ii. Enzymes
1. Control chemical reactions in all living organisms
iii. Provide structure to all living organisms
iv. DNA is in the nucleus and needs to stay there
1. So therefore the instructions to make proteins must be carried outside the
nucleus!
v. Proteins are chains of amino acids made by the protein factory in the cytoplasm---the
ribosomes!
c. In order to get the DNA information from the nucleus to the cytoplasm, we need to transcribe
the DNA into what is called messenger RNA (mRNA)
i. mRNA carries the information out of the nucleus into the ribosome
d.
e. DNA vs RNA
i. RNA contains different nitrogen bases than DNA
1. DNA: A:T-and C:G
2. RNA: A:U and C:G
f. Transcription
i. The process of making mRNA from DNA
ii. A single unwound DNA strand is the template
iii. Match the bases!
1. DNA: A—T—C—G—A—G—T—C—A—T—C—G—A—T—C
2. mRNA: U—A—G—C—U—C—A—G—U—A—G—C—U—A—G
g. How does mRNA code for proteins?
i. mRNA leaves the nucleus
ii. goes to the ribosome in cytoplasm
iii. proteins are built from instructions on the mRNA
iv. mRNA codes for amino acids in triplets!
1. A codon is a block of 3 mRNA bases
v. This means that there are four different letters for each base (4x4x4)=64 possible
combinations for amino acids but only 20 amino acids are present in life, so therefore
some combinations code for the same amino acid
h. Translation
i. The mRNA strand is read by the ribosome in triplets, called the codon
ii. One start codon---AUG—or MET
iii. Three stop codons
iv. A protein will be what lies with the START to STOP codons! (You must always start with
AUG in order to have a protein)
v. The 3 base codon corresponds to a particular amino acid in the amino acid chart
vi. The tRNA carries, or transports, the amino acid that was created by the ribosome and
strings them together to form proteins
1. A block of 3 tRNA bases is called an anti-codon
2.
vii.
viii.
ix.
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xi.
1.
The anticodon carries (transports) the amino acid after its created to string it
together with other amino acids to form proteins
To sum up translation (mRNA to protein)
1. The instructions for the amino acid are coded for in mRNA
2. The ribosome reads the messenger RNA and creates the amino acids
3. The transfer RNA (tRNA) carries the amino acids and helps string them together
to form a protein.
DNA: T-A-C-G-C-A-T-C-G-A-T-C
mRNA: A-U-G-C-G-U-A-G-C-U-A-G
tRNA: U-A-C-G-C-A-U-C-G-A-U-C
Amino Acid: MET-ARG-SER-STOP
III. Genes and Gene Expression
a. Genes are molecular units of heredity in all living organisms!
b. Gene expression is the process by which information from a gene is used in the synthesis of a
functional gene product.
i. These are often proteins
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ii. In other words: Gene expression can be broken down to this:
1. Does the gene show itself or not in an organism
Gene expression is complicated and requires all of the following parts!
a.
Gene expression requires this thing called an operon
a. Operons are segments of DNA where a transcription factor (a protein that binds to specific DNA
sequences, thereby controlling the rate of transcription of genetic information from DNA to
messenger RNA) can bind
b. The operon regulates gene expression!
Control of Gene expression
a. How a gene expresses itself is based off the function of the cell
i. All cells contain same DNA, so all cells have full complement of genes
1. The cell’s function determines how/what genes are expressed
b. 4 levels (stages) where gene expression can be controlled in eukaryotes
i. Transcriptional
1. Determines the rate of transcription or if transcription even occurs
2. Regulated by transcription factors!
ii. Post transcriptional
1. Determines the processing of the mRNA strand
iii. Translational
1. Involves the ability of the mRNA to bind to ribosomes
iv. Post translational
1. Involves changes needed for the polypeptide to become functional
a. Remember: Polypeptide is a long, continuous chain of amino acids!
I.
II.
Mutations
a. Mutations are changes in the DNA that affect genetic information!
b. What causes mutations?
i. Two ways:
1. Inherited from parent to child (sex cells)
2. Acquired
a. Environment
b. DNA replication issues after birth
c. Point Mutation
i. Change in one to three nucleotide base pairs
1. Substitution:
a. THE FAT CAT ATE THE RAT
b. THE FAT HAT AT THE RAT (C in cat changed to H)
2. Insertion:
a. THE FAT CAT ATE THE RAT
b. THE FAT CAT XLW ATE THE RAT (XLW inserted into sequence)
3. Deletion:
a. THE FAT CAT ATE THE RAT
b. THE FAT ATE THE RAT (CAT was deleted)
d. Frameshift Mutation
i. Shifts the way that the sequence is read in the genetic message
ii. May change protein in a way it is not able to perform its function!
1. Insertion
a. THE FAT CAT ATE THE RAT
b. THE FAT HCA TAT ETH ERA T (H inserted before CAT, shifts everything
since codon is read in threes)
2. Deletion:
a. THE FAT CAT ATE THE RAT
b. TEF ATC ATA TET GER AT (H deleted from THE, shifts everything to the
left)
e. Chromosomal Mutations
i. Can change the number of chromosomes
ii. Can change the structure of entire chromosomes
1. Original Chromosome:
a. ABC DEF
2. Deletion
a. AC DEF
3. Duplication
a. ABBC DEF
4. Inversion
a. AED CBF
5. Translocation
a. ABC GHI JKL DEF
Significance of mutations
a. Most are neutral
i. Eye color
b.
c.
ii. Birth marks
Some are harmful
i. Sickle cell anemia
ii. Down syndrome (chromosomal)
Some are beneficial
i. Sickle cell anemia can result in malaria immunity
ii. Immunity to HIV (CCR5-Delta32 gene in northern Europeans)