Name: ___________________________________ Period: ____
Lesson 7.1: From DNA to Proteins
Key Concept
The central dogma of molecular biology can be summed up as DNA → RNA → Protein. Starting in the early 1900s, several researchers made important discoveries about DNA and how it codes for proteins.
Three types of RNA are also involved in protein synthesis: mRNA, rRNA, and tRNA.
Lesson Objectives
• State the central dogma of molecular biology.
• Describe the structure of RNA, and identify the three main types of RNA.
Central Dogma of Biology
1.
DNA is found in________________________________________.
– eukaryotic cells, chromosomes always remain in the nucleus
– proteins are made at ribosomes in the cell
2.
How do the instructions in DNA get to the site of protein synthesis outside the nucleus?
3.
Who coined the phase of the central dogma of biology?
4.
What does the central dogma of biology say?
SIMILARITIES & DIFFERENCES BETWEEN DNA & RNA
Place a check mark in each column that applies indicating what components are found in DNA &
RNA.
Component
Deoxyribonucleic Acid
Ribonucleic Acid
Deoxyribose present
Ribose present
DNA RNA
Phosphate present
Adenine present
Thymine present
Guanine present
Cytosine present
Uracil present
Formed from nucleotides
Double stranded
Single stranded
Remains in nucleus
Moves out of nucleus
Contains a chemical message or code
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List 4 major differences between DNA & RNA in the chart below. Make sure what you list on the lefthand side complements what you list on the right-hand side.
RNA DNA
Three types of RNA and their functions.
Type of RNA Function Picture
Transcription
Using your textbook complete the following questions and activities.
1.
What is transcription?
2.
During transcription, a strand of _____________is made that is complementary to a strand of DNA.
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Figure 1
3.
What nitrogenous base pairs up with adenine in Figure 1 above? _________________
4.
What nitrogenous base pairs up with thymine in Figure 1 above? _________________
Steps of Transcription
1. What are the three steps of transcription?
2. Initiation is the beginning of transcription. It occurs when the enzyme RNA polymerase binds to a region of a gene called the _________________.
3. When RNA polymerase binds to DNA what does DNA do?
4. What is RNA polymerase?
5. What happens during elongation?
6. What happens during the termination step?
Processing mRNA
1.
What other processes, in eukaryotes, must the mRNA go through before it leaves the nucleus?
2.
What does splicing do to the mRNA?
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3.
What are the regions of mRNA called that code for proteins? _____________________
4.
What are the regions of mRNA called that do not code for proteins?
__________________
5.
What does editing do to the mRNA?
6.
What three things does polyadenylation do to the mRNA?
7.
What do a string of A’s at the end of mRNA signal?
Figure 2
The Genetic Code
1.
How is the information in a gene encoded?
2.
How many nitrogenous bases make-up the genetic code? ___________
3.
What is a polynucleotide chain?
4.
Groups of three letters (nitrogenous bases) combine to form code “words” called
_________________.
5.
What does each codon stand for or encode for? _________________________
6.
How many common amino acids are there in proteins? ___________________
7.
How many possible codons are there in the genetic code? _________________
8.
To see how scientists cracked the genetic code, go to this link: http://www.dnalc.org/view/16494-Animation-22-DNA-words-are-threeletters-long-.html
.
a.
Which two scientists cracked the genetic code?
b.
What did they figure out?
c.
What type of bacteria did they use to conduct their studies? _______________ d.
What codon signals the end of transcription? ______________
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9.
What do most academic biology students use to crack the genetic code?
______________________
How to read a Codon Chart and a Codon Wheel
RNA is the instructions for making proteins. Ribosomes use RNA to make amino acid chains that later get folded into proteins. Scientists have developed the Codon Chart and the Codon Wheel to read RNA fragments and figure out what amino acid sequence will be made.
Figure 3
How to read the Codon Chart:
The codon chart gives the same information as the codon wheel. The first letter of the codon is on the left side. Second letter is on the top, and the third letter is on the right side. Where all the points meet, you will find the amino acid that codon represents. A list of the full names for each of the abbreviations given for the amino acids will be given to you when we do the transcription and translation lab.
1.
Looking at the Codon Chart pictured above, try using the chart to read the RNA sequence: AUC-
GUA-AGG. a.
AUC = _____________________ b.
GUA = ____________________ c.
AGG = ____________________
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How to read the Codon Wheel:
Figure 4
Read from the inside out!!! For example, if the RNA sequence is: AUG-CCA-GAU, the codons are
AUG, CCA, and GAU. To read the codon AUG you begin at the center of the Codon Wheel at letter ’A’, then move to the next ring of letters and find the letter ’U’, next move to the next ring and find the letter ’G’, and finally you reach the outermost ring which will provide the name of the amino acid that the RNA sequence coded for. In this case AUG codes for Methionine.
1.
Try and decode the last two codons: CCA and GAU on your own. a.
CCA = ________________________ b.
GAU = _______________________
Reading the Genetic Code
1.
What is the start codon? ______________
2.
What two things does AUG code for? _______________________
3.
What codon establishes the reading frame of mRNA? ____________________
4.
What is the reading frame?
5.
How is the mRNA molecule read or the genetic code?
6.
Which three codons code for stop codons? _____________________________
7.
Do the stop codons also code for amino acids? ______________________
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Characteristics of the Genetic Code
The genetic code has a number of important characteristics.
• The genetic code is universal. All known living things have the same genetic code. This shows that all
organisms share a common evolutionary history.
1.
“The genetic code is universal.” Explain this statement.
• The genetic code is unambiguous. Each codon codes for just one amino acid (or start or stop).
1.
What might happen if codons encoded more than one amino acid?
• The genetic code is redundant. Most amino acids are encoded by more than one codon.
1.
In Figure 4 (the codon wheel on the previous page), how many codons code for the amino acid threonine?
2.
What might be an advantage of having more than one codon for the same amino acid?
Translation
1.
What is the purpose of translation in relationship to the central dogma of molecular biology?
2.
Where does mRNA go after it leaves the nucleus? _______________________
3.
What are ribosomes made up of?
___________________________________________________
4.
What role do the ribosomes play in translation?
5.
What type of RNA brings amino acids to the ribosomes in correct sequence?
____________
6.
Explain the structure of tRNA.
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7.
Codons and anti-codons. Codons code for amino acids; tRNA has an anti-codons for which amino acid it carries which complement codons brought to the ribosomes by mRNA. An anticodon is complementary to the codon for an amino acid. For example, the amino acid lysine has the codon AAG, so the anticodon is UUC. What would be the anti-codon for each of the codons listed below? Remember codons encode for amino acids.
Codon
AUG
Anti-codon Amino Acids
AAA
GUA
8.
Watch the short video at the following link: http://www.youtube.com/watch?v=B6O6uRb1D38&feature=related (1:29).
a.
What codon starts the translation process (give me the three letter codon)? ___________ b.
What codon stops the translation process (give me the three letter codon)? ___________ c.
What type of bonds form between the amino acids? _______________________ d.
In what organelle does translation take place? _________________________
9.
What can happen to a polypeptide chain after it is synthesized?
10.
Where do proteins go to be modified for the specific jobs that they will do?
_____________________
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