Cellular respiration is an ATP-producing catabolic process in which the ultimate electron acceptor is an inorganic molecule, such as oxygen. It is the release of energy from organic compounds by metabolic chemical oxidation in the mitochondria within each cell. Carbohydrates, proteins, and fats can all be metabolized as fuel, but cellular respiration is most often described as the oxidation of glucose, as follows:
C6H12O6 + 6O2 → 6CO2 + 6H2O + 686 kilocalories of energy/mole of glucose oxidized
Cellular respiration involves glycolysis, the Krebs cycle, and the electron transport chain. Glycolysis is a catabolic pathway that occurs in the cytosol and partially oxidizes glucose into two pyruvate (3-C). The Krebs cycle is also a catabolic pathway that occurs in the mitochondrial matrix and completes glucose oxidation by breaking down a pyruvate derivative (Acetyl-CoA) into carbon dioxide. These two cycles both produce a small amount of ATP by substrate-level phosphorylation and NADH by transferring electrons from substrate to NAD+ (Krebs cycle also produces FADH2 by transferring electrons to FAD). The electron transport chain is located at the inner membrane of the mitochondrion, accepts energized electrons from reduced coenzymes that are harvested during glycolysis and Krebs cycle, and couples this exergonic slide of electrons to ATP synthesis or oxidative phosphorylation. This process produces 90% of the ATP.
Cells respond to changing metabolic needs by controlling reaction rates. Anabolic pathways are switched off when their products are in ample supply. The most common mechanism of control is feedback inhibition. Catabolic pathways, such as glycolysis and the Krebs cycle, are controlled by regulating enzyme activity at strategic points. A key control point of catabolism is the third step of glycolysis, which is catalyzed by an allosteric enzyme, phosphofructokinase. The ratio of ATP to ADP and AMP reflects the energy status of the cell, and phosphofructokinase is sensitive to changes in this ratio. Citrate and ATP are allosteric inhibitors of phosphofructokinase, so when their concentration rise, the enzyme slows glycolysis. As the rate of glycolysis slows, the Krebs cycle also slows since the supply of Acetyl-CoA is reduced. This synchronizes the rates of glycolysis and the Krebs cycle. ADP and AMP are allosteric activators for phosphofructokinase, so when their concentrations relative to ATP rise, the enzyme speeds up glycolysis, which speeds of the Krebs cycle.
Cellular respiration is measure in three manners: the consumption of O2 (how many moles of O2 are consumed in cellular respiration?), production of CO2 (how many moles of CO2 are produced in cellular respiration?), and the release of energy during cellular respiration.
PV = nRT is the formula for the inert gas law, where P is the pressure of the gas, V is the volume of the gas, n is the number of molecules of gas, R is the gas constant, and T is the temperature of the gas in degrees K. This law implies several important things about gases. If temperature and pressure are kept constant then the volume of the gas is directly proportional to the number of molecules of the gas. If the temperature and volume remain constant, then the pressure of the gas changes in direct proportion to the number of molecules of gas. If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume. If the temperature changes and the number of gas molecules is kept constant, then either pressure or volume or both will change in direct proportion to the temperature.
Hypothesis:
The respirometer with only germinating peas will consume the largest amount of oxygen and will convert the largest amount of CO2 into K2CO3 than the respirometers with beads and dry peas and with beads alone. The temperature of the water baths directly effects the rate of oxygen consumption by the contents in the respirometers (the higher the temperature, the higher the rate of consumption).
Materials:
The following materials are necessary for the lab: 2 thermometers, 2 shallow baths, tap water, ice, paper towels, masking tape, germinating peas, non-germinating (dry) peas, glass beads, 100 mL graduated cylinder, 6 vials, 6 rubber stoppers, absorbent and non- absorbent cotton, KOH, a 5-mL pipette, silicon glue, paper, pencil, a timer, and 6 washers.
Methods:
Prepare a room temperature and a 10oC water bath. Time to adjust the temperature of each bath will be necessary. Add ice cubes to one bath until the desired temperature of 10oC is obtained.
Fill a 100 mL graduated cylinder with 50 mL of water. Add 25 germinating peas and determine the amount of water that is displaced. Record this volume of the 25 germinating peas, then remove the peas and place them on a paper towel. They will be used for respirometer 1. Next, refill the graduated cylinder with 50 mL of water and add 25 non-germinating peas to it. Add glass beads to the graduated cylinder until the volume is equivalent to that of the expanded germinating peas. Remove the beads and peas and place on a paper towel. They will be used in respirometer 2. Now, refill the graduated cylinder with 50 mL of water. Determine how many glass beads would be required to attain a volume that is equivalent to that of the germinating peas. Remove the beads. They will be used in respirometer 3. Then repeat the procedures used above to prepare a second set of germinating peas, dry peas and beads, and beads to be used in respirometers 4,5,and 6.
Assemble the six respirometers by obtaining 6 vials, each with an attached stopper and pipette. Then place a small wad of absorbent cotton in the bottom of each vial and, using the pipette or syringe, saturate the cotton with 15 % KOH. Be sure not to get the KOH on the sides of the respirometer. Then place a small wad of non-absorbent cotton on top of the KOH-soaked absorbent cotton. Repeat these steps to make the other five respirometers. It is important to use about the same amount of cotton and KOH in each vial.
Next, place the first set of germinating peas, dry peas and beads and beads alone in vials 1,2, and 3. Place the second set of germinating peas, dry peas and beads, and glass beads in vials 4,5, and 6. Insert the stoppers in each vial with the proper pipette. Place a washer on each of the pipettes to be used as a weight.
Respirometer
Temperature
Contents
1
Room
Germinating Peas
2
Room
Dry Seeds + Beads
3
Room
Beads
4
10oC
Germinating Peas
5
10oC
Dry Seeds + Beads
6
10oC
Beads
Make a sling using masking tape and attach it to each side of the water baths to hold the pipettes out of the water during the equilibration period of 10 minutes. Vials 1,2, and 3 should be in the bath containing water at room temperature. Vials 4, 5, and 6 should be in the bath containing water that is 10oC. After the equilibration period, immerse all six respirometers into the water completely. Water will enter the pipette for a short distance and stop. If the water does not stop, there is a leak. Make sure the pipettes are facing a direction from where you can read them. The vials should not be shifted during the experiment and your hands should not be placed in the water during the experiment.
Allow the respirometers to equilibrate for three more minutes and then record the initial water reading in each pipette at time 0. Check the temperature in both baths and record the data. Every five minutes for 20 minutes take readings of the water’s position in each pipette, and record.
Results:
Table 1: Measurement of O2 Consumption by Soaked and Dry Pea Seeds at Room Temperature and 10˚C Using Volumetric Methods
Beads Alone
Germinating Peas
Dry Peas and Beads
Reading at time X
Diff.
Reading at time X
Diff.
Corrected Diff.∆
Reading at time X
Diff.
Corrected Diff.∆
Initial-0
1.38
1.35
1.47
0-5
1.38
0
1.16
.19
.19
1.46
.01
.01
5-10
1.38
0
1.04
.31
.31
1.44
.03
.03
10-15
1.38
0
0.93
.42
.42
1.43
.04
.04
15-20
1.38
0
0.57
.78
.78
1.42
.05
.05
Initial-0
1.40
1.32
1.40
0-5
1.39
.01
1.20
.12
.11
1.40
0
.01
5-10
1.38
.02
1.11
.21
.19
1.40
0
.02
10-15
1.38
.02
1.00
.32
.30
1.39
.01
.01
15-20
1.38
.02
0.95
.37
.93
1.38
.02
0
In this activity, you are investigating both the effects of germination versus non-germination and warm temperature versus cold temperature on respiration rate. Identify the hypothesis being tested on this activity. The rate of cellular respiration is higher in the germinating peas in cold than in the beads or non-germinating peas; the cooler temperature in the cold water baths slows the process of cellular respiration in the both germinating and non-germinating peas.
This activity uses a number of controls. Identify at least three of the controls, and describe the purpose of each. The constant temperature in the water baths yielding stable readings, the unvarying volume of KOH from vial to vial leading to equal amounts of carbon dioxide consumption, identical equilibration periods for all the respirometers, precise time intervals between measurements, and glass beads acting as a control for barometric pressure all served as controls.
Describe and explain the relationship between the amount of oxygen consumed and time. There was a constant, gradual incline in the amount of oxygen consumed over precise passage of time.
Condition
Calculations
Rate in mL O2/ minute
Germinating Peas/ 10 oC
(1.40-1.38)
20 min.
.001
Germinating Peas/ 20 oC
(1.35-.57)
20 min.
.040
Dry Peas/ 10 oC
(1.40-1.38)
20 min.
.001
Dry Peas/ 20 oC
(1.47-1.42)
20 min.
.003
Why is it necessary to correct the readings from the peas with the readings from the beads? The beads served as a control variable, therefore, the beads experienced no change in gas volume.
Explain the effects of germination (versus non-germination) on pea seed respiration. The germinating seeds have a higher metabolic rate and needed more oxygen for growth and survival. The non-germinating peas, though alive, needed to consume far less oxygen for continued subsistence.
Above is a sample graph of possible data obtained for oxygen consumption by germinating peas up to about 8 oC. Draw in predicted results through 45oC. Explain your prediction. Once the temperature reached a certain point, the enzymes necessary for cellular respiration denatured and germination (and large amounts of oxygen consumption) was inhibited.
What is the purpose of KOH in this experiment? The KOH drops absorbed the carbon dioxide and caused it to precipitate at the bottom of the vial and no longer able to effect the readings.
Why did the vial have to be completely sealed under the stopper? The stopper at the top of the vial had to be completely sealed so that no gas could leak out of the vial and no water would be allowed into the vial.
If you used the same experimental design to compare the rates of respiration of a 35g mammal at 10 oC, what results would you expect? Explain your reasoning. Respiration would be higher in the mammal since they are warm-blooded and endothermic.
If respiration in a small mammal were studied at both room temperature (21 oC) and 10 oC, what results would you predict? Explain your reasoning. Respiration would be higher at 21 degrees because it would be necessary for the animal to maintain a higher body temperature. The results would proliferate at 10 degrees because the mammal would be required to retain its body temperature at an even lower temperature in comparison to room temperature.
Explain why water moved into the respirometer pipettes. While the peas underwent cellular respiration, they consumed oxygen and released carbon dioxide, which reacted with the KOH in the vial, resulting in a decrease of gas in the pipette. The water moved into the pipette because the vial and pipette were completely submerged into the bath.
Design an experiment to examine the rates of cellular respiration in peas that have been germinating for 0, 24, 48, and 72 hours. What results would you expect? Why? Respirometers could be set up with respirometer 1 containing non-germinating peas, respirometer 2 holding peas that have been germinating 24 hours, 3 would contain the peas that germinated 48 hours, and 4 would hold the peas that germinated 72 hours. All the respirometers should have the KOH added to the bottom in the same manner as in lab described earlier. The respirometers should be placed in baths with the same temperature for all the respirometers. The seeds that have not begun germination would consume very little oxygen. The peas that have been germinating for 72 hours will have the greatest amount of oxygen consumption, while the other two samples will consume a medium (in comparison to respirometers 1 and 4 results) amount of oxygen.
Error Analysis:
Numerous errors could have occurred throughout the lab. The temperature of the baths may have been allowed to fluctuate, the amounts of peas, beads, KOH, and cotton may have varied from vial to vial damaging the results, and these problems would have occurred only during set up. Air may have been allowed to creep into the vial via a leaky stopper or poorly sealed pipette. Timing for the equilibration of the respirometers and the five-minute time intervals may have been erroneous. It was somewhat difficult to read the markings on the pipettes and so errors are always likely. Mathematical inaccuracies may have taken place when filling out the table and finding the corrected difference by using the formula provided.
Discussion and Conclusion:
The lab and the results gained from this lab demonstrated many important things relating to cellular respiration. It showed that the rates of cellular respiration are greater in germinating peas than in non-germinating peas. It also showed that temperature and respiration rates are directly proportional; as temperature increases, respiration rates increase as well. Because of this fact, the peas contained by the respirometers placed in the water at 10 oC carried on cellular respiration at a lower rate than the peas in respirometers placed in the room temperature water. The non-germinating peas consumed far less oxygen than the germinating peas. This is because, though germinating and non-germinating peas are both alive, germinating peas require a larger amount of oxygen to be consumed so that the seed will continue to grow and survive.
In the lab, CO2 made during cellular respiration was removed by the potassium hydroxide (KOH) and created potassium carbonate (K2CO3). It was necessary that the carbon dioxide be removed so that the change in the volume of gas in the respirometer was directly proportional to the amount of oxygen that was consumed. In the experiment water will moved toward the region of lower pressure. During respiration, oxygen will be consumed and its volume will be reduced to a solid. The result was a decrease in gas volume within the tube, and a related decrease in pressure in the tube. The respirometer with just the glass beads served as a control, allowing changes in volume due to changes in atmospheric pressure and/or temperature.
Overview: In this experiment, you will work with seeds that are living but dormant. A seed contains an embryo plant and a food supply surrounded by a seed coat. When the necessary conditions are met, germination occurs, and the rate of cellular respiration greatly increases. In this experiment you will measure oxygen consumption during germination. You will measure the change in gas volume in respirometerscontaining either germinating or non-germinating pea seeds. In addition, you will measure the rate of respiration of these peas at two different temperatures.
Objectives: Before doing this laboratory you should understand:
how a respirometer works in terms of the gas laws; and
the general processes of metabolism in living organisms.
After doing this laboratory you should be able to:
calculate the rate of cell respiration from experimental data.
relate gas production to respiration rate; and
test the effect of temperature on the rate of cell respiration in ungerminated versus germinated seeds in a controlled experiment.
Introduction: Cellular respiration is the release of energy from organic compounds by metabolic chemical oxidation in the mitochondria within each cell. Cellular respiration involves a series of enzyme-mediated reactions. The equation below shows the complete oxidation of glucose. Oxygen is required for this energy-releasing process to occur.
C6H12O6 + 6O2 —–> 6 CO2 + 6 H2O + 686 kilocalories of energy / mole of glucose oxidized
By studying the equation above, you will notice there are three ways cellular respiration could be measured. One could measure the:
1. Consumption of O2 ( How many moles of oxygen are consumed in cellular respiration?)
2. Production of CO2 ( How many moles of carbon dioxide are produced by cellular respiration?)
3. Release of energy during cellular respiration.
In this experiment, the relative volume of O2 consumed by germinating and non-germinating (dry) peas at two different temperatures will be measured.
Background Information: A number of physical laws relating to gases are important to the understanding of how the apparatus that you will use in this exercise works. The laws are summarized in the general gas law that states:
PV = nRT
where
P is the pressure of the gas,
V is the volume of the gas,
n is the number of molecules of gas,
R is the gas constant ( its value is fixed), and
T is the temperature of the gas (in K0).
This law implies the following important concepts about gases:
1. If temperature and pressure are kept constant, then the volume of the gas is directly proportional to the number of molecules of gas.
2. If the temperature and volume remain constant, then the pressure of the gas changes in direct proportion to the number of molecules of gas present.
3. If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume.
4. If the temperature changes and the number of gas molecules is kept constant, then either pressure or volume ( or both ) will change in direct proportion to the temperature.
It is also important to remember that gases and fluids flow from regions of high pressure to regions of low pressure.
In this experiment, the CO2 produced during cellular respiration will be removed by potassium hydroxide (KOH) and will form solid potassium carbonate (K2CO3) according to the following reaction.
CO2 + 2 KOH —-> K2CO3 + H2O
Since the carbon dioxide is being removed, the change in the volume of gas in the respirometer will be directly related to the amount of oxygen consumed. In the experimental apparatus if water temperature and volume remain constant, the water will move toward the region of lower pressure. During respiration, oxygen will be consumed. Its volume will be reduced, because the carbon dioxide produced is being converted to a solid. The net result is a decrease in gas volume within the tube, and a related decrease in pressure in the tube. The vial with glass beads alone will permit detection of any changes in volume due to atmospheric pressure changes or temperature changes. The amount of oxygen consumed will be measured over a period of time. Six respirometers should be set up as follows:
Respirometer
Temperature
Contents
1
Room
Germinating seeds
2
Room
Dry Seeds and Beads
3
Room
Beads
4
100C
Germinating Seeds
5
100C
Dry Seeds and Beans
6
100C
Beads
Procedure: 1.Prepare a room-temperature bath (approx. 25 degrees Celsius) and a cold-water bath (approx. 10 degrees Celsius).
2.Find the volume of 25 germinating peas by filling a 100mL graduated cylinder 50mL and measuring the displaced water.
3.Fill the graduated cylinder with 50mL water again and drop 25 non-germinating peas and add enough glass beads to attain an equal volume to the germinating peas.
4.Using the same procedure as in the previous two steps, find out how many glass beads are required to attain the same volume as the 25 germinating peas.
5.Repeat steps 2-4. These will go into the 10-degree bath.
6.To assemble 6 respirometers, obtain 6 vials, each with an attached stopper and pipette. Number the vials. Place a small wad of absorbent cotton in the bottom of each vial and, using a dropper, saturate the cotton with 15% KOH (potassium hydroxide). It is important that the same amount of KOH be used for each respirometer.
7.Place a small wad of dry, nonabsorbent cotton on top of the saturated cotton.
8.Place the first set of germinating peas, dry peas & beads, and glass beads in the first three vials, respectively. Place the next set of germinating peas, dry peas & beads, and glass beads in vials 4, 4, and 6, respectively. Insert the stopper with the calibrated pipette. Seal the set-up with silicone or petroleum jelly. Place a weighted collar on each end of the vial. Several washers around the pipette make good weights.
9.Make a sling of masking tape attached to each side of the water baths. This will hold the ends of the pipettes out of the water during an equilibration period of 7 minutes. Vials 1, 2, and 3 should be in the room temperature bath, and the other three should be in the 10 degree bath.
10.After 7 min., put all six set-ups entirely into the water. A little water should enter the pipettes and then stop. If the water continues to enter the pipette, check for leaks in the respirometer.
11.Allow the respirometers to equilibrate for 3 more minutes and then record the initial position of the water in each pipette to the nearest 0.01mL (time 0). Check the temperature in both baths and record. Record the water level in the six pipettes every 5 minutes for 20 minutes.
Table 5.1: Measurement of O2 Consumption by Soaked and Dry Pea Seeds at Room Temperature (250C) and 100C Using Volumetric Methods.
Temp
(oC)
Time
(min)
Beads Alone
Germinating Peas
Dry Peas and Beans
Reading at time X
Diff*
Reading at time X
Diff*
Corrected Diff. ^
Reading at time X
Diff*
Corrected diff ^
Initial – 0
0-5
5- 10
10 -15
15-20
Initial – 0
0-5
5- 10
10 -15
15-20
* difference = ( initial reading at time 0) – ( reading at time X )
^ corrected difference = ( initial pea seed reading at time 0 – pea seed reading at time X) – ( initial bead reading at time X).
Analysis of Results: 1. In this investigation, you are investigating both the effect of germination versus non-germination and warm temperature versus cold temperature on respiration rate. Identify the hypothesis being tested in this activity.
5. From the slope of the four lines on the graph, determine the rate of oxygen consumption of germinating and dry peas during the experiments at room temperature and 100C. Recall that rate = delta Y/delta X.
Table 5.2
Condition
Show Calculations Here
Rate in ml.O2 / min
Germinating Peas/100C
Germinating peas /Room Temperature
Dry peas/100C
Dry Peas /Room Temperature
6. Why is it necessary to correct the readings from the peas with the readings from the beads?
10. If you used the same experimental design to compare the rates of respiration of a 25 g. reptile and a 25 g. mammal, at 100C, what results would you expect/ Explain your reasoning.
4. What are the repeating subunits called that make up DNA?
5. Name the 3 parts of a DNA nucleotide.
6. Sketch and label a DNA nucleotide.
7. Name the 4 nitrogen bases on DNA.
8. What is the difference between a purine & a pyrimidine?
9. Name 2 purines.
10. Name 2 pyrimidines.
11.Who is responsible for determining the structure of the DNA molecule & in what year was this done?
12. The model of DNA is known as a ____________________________ because it is composed of two ___________________ chains wrapped around each other.
13. What makes up the sides of a DNA molecule?
14. What makes up the “steps” of a DNA molecule?
15. How did Rosalind Franklin contribute to determining the structure of DNA?
16. What type of bonds holds the DNA bases together? Are they strong or weak bonds?
17. What makes up the “backbone” of the DNA molecule?
18. On DNA, a ____________________ base will always pair with a __________________ base.
19. What is the most common form of DNA found in organisms?
20. How many base pairs are in a full turn or twist of a DNA molecule?
21. Name the complementary base pairs on DNA.
22. How many hydrogen bonds link cytosine & guanine? adenine & thymine?
23. How does the nucleotide sequence in one chain of DNA compare with the other chain of DNA?
24. Why must DNA be able to make copies of itself?
25. Define DNA replication.
26. What is the first step that must occur in DNA replication?
27. What acts as the template in DNA replication?
28. What is a replication fork?
29. What enzymes help separate the 2 strands of nucleotides on DNA? What bonds do they break?
30. What is the function of DNA polymerases?
31. ____________________ are joined to replicating strands of DNA by ________________ bonds.
32. If the sequence of nucleotides on the original DNA strand was A – G – G – C – T – A, what would be the nucleotide sequence on the complementary strand of DNA?
33. Does replication of DNA begin at one end and proceed to the other? Explain.
34. Why does DNA replication take place at many places on the molecule simultaneously?
35. When replication is complete, how do the 2 new DNA molecules compare to each other & the original DNA molecule?
36. Is DNA replicated (copied) before or after cell division?
37. Sketch & label DNA replication. (Figure 10-5, page 188)
38. What is the error rate in DNA replication? What helps lower this error rate to 1 in 1 billion nucleotides?
39. What is a mutation?
40. Name several things that can cause DNA mutations.
Section 10-2 RNA
41. What sugar is found on DNA?
42. What base is missing on RNA, & what other base replaces it?
43. Uracil will pair with what other on DNA?
44. Is RNA double or single stranded?
45. Name the 3 types of RNA and tell the shape of each.
46. Which type of RNA copies DNA’s instructions in the nucleus?
47. Which type of RNA is most abundant?
48. What does tRNA transport?
49. What 2 things make up ribosomes?
50. Define transcription.
51. In what part of a cell are proteins made?
52. What is RNA polymerase & tell its function.
53. What are promoters?
54. Where does RNA polymerase bind to the DNA it is transcribing?
55.What makes the beginning of a new gene on DNA in eukaryotes?
56. What do promoters mark the beginning of on prokaryotic DNA?
57. When a promoter binds to DNA, What happens to the double helix?
58. Are both strands of DNA copied during transcription?
59. As RNA polymerase moves along the DNA template strand, what is being added?
60. What bases pair with each other during transcription?
61. What is the termination signal?
62. What happens when RNA polymerase reaches the termination signal?
63. What are the products of transcription called?
64. Transcripts are actually ____________________________ molecules.
65. In transcription, ________________________’s instructions for making a protein
are copied by _______________________.
66. Which RNA molecules are involved in the synthesis (making) of a protein?
67. What happens to the newly made mRNA molecule following transcription in the nucleus?
Section 10-3 Protein Synthesis
68. What makes up proteins, what are the subunits called, & what bonds them together?
69. How many different kinds of amino acids make up proteins?
70. What determines how protein polypeptides fold into 3-dimensional structures?
71. Why does a protein need a 3-dimensional structure?
72. What is the genetic code & why is it important?
73. What is a codon & what does each codon code for?
74. How many codons exist?
75. Name the amino acid coded for by each of these codons:
a. UUA
b. AUU
c. UGU
d. AAA
e. GAG
f. UAA
76. What codon starts protein synthesis?
77. What codons stop protein synthesis?
78. Proteins are synthesized (made) at what organelle in the cytosol?
79. Sketch and label a tRNA molecule & tell its function.
80. Define translation & tell how it starts.
81. Where are amino acids found in a cell & how are they transported?
82. What is an anticodon & where is it found on tRNA?
83. What codon on mRNA would bind with these anticodons: (use table 10-1, page 194)
a. AAA
b. GGA
c. UAC
d. CGU
84. What are ribosomes made of and in what 2 places can they be found in a cell?
85. What is the difference between proteins made by free ribosomes & those made by attached, membrane proteins on the ER?
86. How many binding sites are found on the ribosomes and what does each site hold?
87. To start making a protein or _________________________________, a ribosome attaches to the ______________________________ codon on the __________________ transcript.
88. The start codon, AUG, pairs with what anticodon on a tRNA molecule?
89. What amino acid does the start codon always carry?
90. What type of bonds are the ones that attach amino acids to each other in a growing polypeptide?
91. __________________________ are linked to make proteins as a ______________________ moves along the mRNA transcript.
92. What ends translation?
93. Can more than one ribosome at a time translate an mRNA transcript? Explain.
94. What determines the primary structure of a protein?
95. What would the translation of these mRNA transcripts produce?
