Download GENETICS and the DNA code NOTES BACKGROUND DNA is the

GENETICS and the DNA code NOTES
BACKGROUND
DNA is the hereditary material of most organisms. It is an organic compound made of two
strands, twisted around one another to form a double helix. Each strand is composed of repeating
units of nucleotides, which themselves are composed of deoxyribose sugar, a phosphate group, and
a nitrogen base. There are four nitrogen bases in DNA – adenine (A), thymine (T), cytosine (C), and
guanine (G). The sequence of these nitrogen bases is the genetic code. Every three bases, or
“letters,” codes for an amino acid, the building block of proteins.
Like DNA, RNA is a nucleic acid made of repeated nucleotides. An RNA nucleotide consists of
ribose sugar, a phosphate group, and a nitrogen base. RNA is very similar to DNA, but differs in a few
important structural details: in the cell, RNA is usually single stranded, while DNA is usually double
stranded; RNA nucleotides contain ribose, while DNA contains deoxyribose (a type of ribose that
lacks one oxygen atom); and RNA has the nucleotide uracil, rather than thymine, which is present in
DNA.
Through the processes of transcription and translation, the cell makes proteins using the code
from DNA. Transcription takes place in the nucleus and involves transferring the information in DNA
through messenger RNA (mRNA). The mRNA is a single strand that is the complement of the
template DNA, except that it uses uracil (U) instead of thymine (T). Once the mRNA is formed, it
leaves the nucleus and goes into the cytoplasm.
Translation takes place in the cytoplasm and is the process of creating a polypeptide from the
information carried on the mRNA. The mRNA binds with a ribosome, which is the site where protein
synthesis takes place. The mRNA moves through the ribosome three nitrogen bases at a time; these
three nitrogen base segments are called a codon, and each codon codes for a particular amino acid.
The transfer RNA (tRNA) has an anticodon that is the complement of the codon and carries the
appropriate amino acid for that codon. This process of adding amino acids continues until there is a
stop codon, signaling the end of the polypeptide. This polypeptide is then folding to make a protein.
Some proteins are made of a single polypeptide, while others are made up of multiple polypeptides
bonded together.
Mutations are changes in a gene in the DNA, which may cause the protein to not form
correctly. These changes can be passed on from a parent, or they can occur during an individual’s
lifetime. The impact of the mutation depends on where and when the change occurs. Some changes
occur in non-coding regions or involve a change that still codes for the same amino acid sequence,
since multiple nitrogen base combinations can code for the same amino acid. These are called silent
mutations and are considered to be neutral. Other mutations can change the protein structure, which
will change the traits of an organism. These changes can be either positive or negative for the
organism.
RNA
DNA
# strands
Nitogen bases
Sugar
Location
In nucleus and cytoplasm
Primary function
Trasnfers genetic information
to aid cell in protein synthesis
Long-term storage of genetic
information; codes fro
proteins
Replication: in nucleus
1. Unzip DNA helix by breaking hydrogen bonds
2. Add DNA nucleotides to exposed strands
Transcription: in nucleus
1. Unzip section of DNA to copy
2. And RNA nucleotides to one side of DNA exposed
3. Modify mRNA by cutting out introns (noncoding mRNA) leaving only exons (coding mRNA)
4. Mature mRNA leaves nucleus
Translation: in cytoplasm
1. Ribosome reads mRNA code at START codon
2. tRNA with anitcodon that complements mRNA brings correct amino acid
3. Ribosome attaches amino acids together
4. Ribosome release mRNA and complete amino acid chain when hits STOP codon
Use the information above to help complete the activity.
Turn the DNA sequence into an amino acid chain. Also include the tRNA anitcodon.
1.
Complimentary DNA
Original DNA
3’
T A C T C G G G G C G C A T C C A A G A G 5’
mRNA codons
Amino acid sequence
tRNA anticodon
2.
Complimentary DNA
Original DNA
3’
T A C G A T C G A T A G C T A G C T A G C 5’
3’
T A C A C G T A T C T T G G C T A G C T A 5’
mRNA codons
Amino acid sequence
tRNA anticodon
3.
Complimentary DNA
Original DNA
mRNA codons
Amino acid sequence
tRNA anticodon
Mutations NOTES
Identify each type of DNA mutation: point, frameshit (insertion), frameshift (deletion)
Which type of mutation (point or frameshift, causes more damage? Why?
Identify each type of chromosomal mutation: insertion, deletion, substitution, inversion, translocation
How are the chromsomal mutations above different from the effects of nondisjunction?
Identify the mutations as: silent muation, missense mutation, nonsense mutation, stop codon
mutation
1. ______________: results in same amino acid; same function
2. ______________: results in code for different amino acid; affects range (ex. Sickle cell
anemia
3. ______________: results in early stop codon; harmful affects (ex. Cystic fibrosis)
4. ______________: results in stop codon turned into another amino acid (chain gets too big);
harmful affects (ex. Familial British dementia)
Name _________________________ Period _____ date _______
DNA Replication and Central Dogma
Identify each figure below: replication, transciption, translation
1.
2. Where does replication occur? ________________________
3. Where does transciption occur? ________________________
4. Where does tranlation occur? ________________________
5. Which process results in amino acid chains? ________________________
6. Which process results in mRNA? _________________________
7. Which process results in more DNA for cellular division? _______________________
Making complimentary DNA (cDNA) strands:
8.
3’
AATTCGCCGGTATTAGACGTT
9.
3’
TATCCCGGAGAGGTCCAATGC
10. 3’ A T C G G G G A A T T A C C C G T T A A
5’
5’
5’
11. What is a codon? ________________________________________________________________
12. What codon means start? ________________________________________________
13. What 3 codons act as termination signals? ________________________________________
14. List ALL of the codons for leucine. __________________________________________________
15. Name one amino acid that has more than one codon. __________________________
16. Name an amino acid that has only one codon __________________________
If the DNA sequence is --- AAA TAT CCG TAG CAA ATG, write the mRNA sequence, tRNA anticodon
sequence, and the six amino acids for this.
DNA:
AAA
TAT
CCG
TAG
CAA
ATG
17. mRNA:__________________________________________________________________
18. Amino acids: __________________________________________________________________
19. tRNA: __________________________________________________________________
20. Given the following three mRNA sequences, 2 code for the same protein. Which two? Circle the
correct sequences
a) AGU UUA GCA ACG AGA UCA
b) UCG CUA GCG ACC AGU UCA
c) AGC CUC GCC ACU CGU AGU
21. A geneticist found that a particular mutation had no effect on the protein coded by a gene. What do
you think is the most likely type of mutation in this gene? Why?
22. Look at the following sequence: THE FAT CAT ATE THE RAT. Delete the first H and regroup the
letters in groups of three- write out the new groups of three. Does the sentence still make sense?
What type of mutation is this an example of?
Below is the base sequence for the normal protein for normal hemoglobin and the base sequence for the
sickle cell hemoglobin.
Normal GGG CTT CTT TTT
Sickle GGG CAT CTT TTT
23. Transcribed and translate the normal and sickle cell DNA.
Normal
Sickle Cell
24. Is sickle cell caused by a point or frameshift mutation. Explain.
25. If the base sequence read GGG CTT CTT AAA instead, would this result in sickle cell hemoglobin?
Explain why or why not.
Fill in the Chart
cDNA
strand
20.
ORIGINAL
DNA triplet
mRNA codon
tRNA anticodon
AAG
21.
GGC
22.
CAG
23.
UUA
24.
AAA
25.
GTA
26.
CUC
27.
ACA
28.
TAT
29.
AGC
30.
AUU
31.
CCA
32.
GGC
mRNA
CODON CHART
for
Amino Acids
Amino Acid