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Complete the following table:

nucleotide DNA RN

B5. Describe DNA replication

1) Label each base given in the diagram below and describe the 4 primary characteristics of DNA.

2) Identify the site of DNA replication within the cell. Nucleus

3) Explain the three major steps, and all of the enzymes involved, in semi-conservative replication of DNA. What is meant by semi-conservative replication?

1. Helicase “unzips” DNA strand 2. DNA polymerase joins DNA bases that are complementary to the template strand. One strand is the original / old one while the other strand is new. = semiconservative replication. Covalent bonds between the backbone and H-bonds between strands are added 3. Proof reading enzyme checks for mistakes

• semiconservative replication means that there is one new and one original strand of DNA

4) Describe the purpose of DNA replication. To make a copy of the DNA for the new cell during cell division

Section  1  Workbook  (unit  2)  ANSWERS      Name:  ____________  

 -­‐Deoxyribose  sugar,  phosphate  group  and  one  of  nitrogen  bases  making  up  a  nucleotide.  

-­‐Double  helix  shape  

-­‐Two  strands  held  together  by  hydrogen  bonds  between  the  nitrogen  bases  

Sugar  phosphate  backbone  

                               A            G                  T                    C      

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5) If a cell is exposed to acidic conditions during cell division, how would this affect the cell’s

ability to divide? Why? Enzymes are proteins so a specific shape is needed in order to function. The change in pH would cause the enzymes, such as helicase and polymerase to denature. When these enzymes denature, they change shape and therefore, will not function anymore so cell division cannot occur.

6) How does the amount of:

a. Adenine compare to the amount of thymine in DNA? Same amount, A pairs with T b. Guanine compare to the amount of cytosine in DNA? Same amount, G pairs with C c. Purines compared to the number of pyrimidines? Same amount

7) How are DNA and RNA chemically similar? Different?

Similar: polymers of nucleotides, phosphate groups, nitrogen bases AGC, & pentose sugar

Different: DNA has thymine while RNA has uracil. RNA single stranded while DNA double stranded with hydrogen bonds, DNA – deoxyribose sugar, RNA – ribose sugar.

B6. Describe recombinant DNA (rDNA)

8) Describe recombinant DNA. Include the enzymes required for the formation of rDNA. Use a diagram to help your explanation. 1. DNA from human – gene of interest is isolated and removed with restriction enzyme (cuts

DNA) 2. Plasmid from bacteria removed and cut with same restriction enzyme 3. Gene put into plasmid = recombined into a single DNA strand = rDNA 4. Put into bacteria – bacteria divide & give off product such as insulin.

9) Describe at least three uses for recombinant DNA.

• Make insulin, human growth hormone, TPA • Create disease resistant plants • Add nutrient to food crop (Golden rice)

 

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B7. Demonstrate an understanding of the process of protein synthesis 10) Complete the following table:

Describe both processes. Use diagrams to help in your explanation

Transcription

1. Helicase opens DNA where gene located 2. RNA polymerase adds complementary RNA bases to create mRNA

molecule – from initiation site to termination site. (DNA serves as template for mRNA)

3. mRNA molecule leaves through nuclear pores to cytoplasm – linear so it fits through the nuclear pores.

Translation

11) Which process, transcription or translation, is depicted here? Label the molecules.

12) Complete the following table:

Describe each molecules’ role in Protein Synthesis

DNA Has instructions on how to make a protein = code

mRNA Copies instructions and takes them to ribosome

tRNA Brings AA to ribosome to be added to polypeptide chain

ribosomes Builds polypeptide chain – site for codons & anticodons to meet

1. Initiation – 2 halves of ribosome (large & small subunits) come around the mRNA molecule and the start codon (AUG) turns on translation

2. Elongation – tRNA brings AA to ribosome. Codon on mRNA matches with anticodon on tRNA (A with U & G with C) and AA left to be added to the polypeptide chain with peptide bonds.

3. Termination - elongation continues until a stop codon is reached (3 of these) which turns off translation. Ribosome separates releasing mRNA & primary protein structure to be bent and folded into its functional shape

ribosome  

Amino  acids  

mRNA   tRNA  

Translation  is  shown  here  

 

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13) Of the 5 nitrogen bases, which one is X in the below diagram? How do you know (support your answer)?

14) Label the following in the diagram below: mRNA (3 times), ribosome, anticodon, tRNA, DNA, amino acid, codon, primary protein, nucleus, cytoplasm.

 

Adenine  has  2  hydrogen  bonds  and  is  a  purine  (double  ring)  

Since  molecule  X  is  on  an  mRNA  molecule,  and  RNA  does  not  have  thymine,  the  pyrimidine  molecule  is  uracil.  

Adenine  

mRNA  

Nucleus  

 

 

cytoplasm  

DNA  

tRNA  

ribosome  

Amino  acid  

anticodon  

codon  

Primary  protein  

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15) Use the aa codon chart to determine the amino acid sequence produced by the section of an mRNA molecule below and determine the DNA strand that provided the instructions.

mRNA= CGC – UAU - UGG DNA= __ GCG – ATA - ACC__

Amino Acids: = Arg – Tyr - Try

16) Use the aa codon chart to predict the amino acid sequence produced by this sequence of bases on a DNA molecule and label transcription and translation

DNA= TAC-GAA-CTT-GGG-TCC

mRNA= AUG -CUU-GAA-CCC-AGG

Amino Acids = ___ Met – Leu – Glu – Pro - Arg

17) What anti-codon would be present on the tRNA that is complementary to the mRNA codons

given? Anti-codon on tRNA always complements mRNA codon

AUG _UAC_

AGA UCU__

UAA _AUU__

CGU GCA___

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18) Explain what would occur during translation of the following DNA sequence if ACG underwent a mutation and was converted to ACT.

Unmutated DNA: GCA CCT ACG GGA ACC DNA mutation: GCA CCT ACT GGA ACC

mRNA: CGU GGA UGA CCU UGG AA sequence: Arg – Gly - stop

Explanation: The mutation causes a stop codon to occur early in the synthesis of the protein. Therefore, the protein will be incomplete and not be able to function.

19) Production of mRNA is called ______transcription_____

20) Production of a protein is called ____translation_________

21) Given the following tRNA sequence, find the DNA strand and polypeptide chain created: tRNA: UAC ACC GCC CUA CCC AAA

mRNA: AUG UGG CGG GAU GGG UUU DNA: TAC ACC GCC CTA CCC AAA AA: Met trp arg asp gly phe

22) In an experiment conducted to study proteins synthesis, radioactive thymine and radioactive uracil were added to a culture of human cells. A few hours later, the culture was analyzed and radioactive mRNA was found.

a. Explain how an mRNA molecule is produced: TRANSCRIPTION • Helicase opens DNA where gene located • RNA polymerase adds complementary RNA bases to create mRNA molecule – from

initiation site to termination site. (DNA serves as template for mRNA) • mRNA molecule leaves through nuclear pores to cytoplasm – linear so it fits

through the nuclear pores.

b. Explain why the mRNA produced is radioactive Because uracil was incorporated into the mRNA molecule causing it to be radioactive.

c. In a different experiment, radioactive uracil was added to a culture of human cells undergoing

DNA replication. What will be the characteristic of the resulting DNA in terms of radioactivity? Explain.

DNA does not have uracil therefore it would not be incorporated into the DNA molecule. So the DNA would NOT be radioactive

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B8. Explain how mutations in DNA affect protein synthesis 23) Give examples of two environmental mutagens that can cause mutations in humans. How do

they cause a mutation?

• Biological: viruses and bacteria that increase the chance of a mutation • Chemical: food additives, hallucinogenic drugs, asbestos, DDT, pesticides, manufactured

chemicals…. affect enzymes of DNA replication, increasing the chance of mutation • Radiation: UV & cosmic rays - increasing the chance of mutation

24) Define transgenic organisms. Give an example. An organism that has the DNA of another organism inserted into it is called a transgenic organism. Example: bacteria with the human insulin gene

25) Use the examples to explain how mutations in DNA change the sequence of amino

acids in a polypeptide chain, and as a result, may lead to genetic disorders. a. point mutations, sickle cell anemia

Changes the amino acid glutamate into valine. This results in abnormal hemoglobin molecule that causes the red blood cell to have a sickle shape that can clog blood vessels and lead to pain.

b. gene mutation, hemophilia / cystic fibrosis A gene mutation that causes a lack of or minimal amount of clotting factors to be produced resulting in excessive bleeding.

c. chromosomal mutation, Trisomy 21

An extra chromosome #21 results in Down’s syndrome. This causes high levels of purines in the blood which leads to mental deficiencies.

26) Define gene therapy. What is its purpose?

= alteration of afflicted individuals’ genes (of the same species) • could help with genetic diseases like cystic fibrosis, Alzheimer’s, some cancers, AIDS

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Types  of  gene  mutations  Here is a section of DNA before a mutation.

DNA: TAC GGG CTC TAG CGA GAT ATT

mRNA: AUG CCC GAG AUC GCU CUA UAA

AA’s: Met Pro Glu Ile Ala Leu stop

27) Insertion mutation - What would happen to the AA sequence above if one extra base (a G at the start of the 3rd codon) were added to the original DNA sequence?

Inserted DNA TAC GGG GCT CTA GCG AGA TAT T Resultant mRNA AUG CCC CGA GAU CGC UCU AUA Mutated AA Met Pro Arg Asp Arg Ser Ile a. What conclusions can you draw regarding the effect of insertion mutations on the polypeptide

chain that would be produced? They cause an incomplete protein to be made – there is an extra base that does not make up a codon. Frameshift mutation compared to the original strand, every aa after the insertion changes.

b. Do you think that insertion mutations would likely improve or negatively impact the intended function of the protein produced? Negative impact

28) Deletion mutation - What would happen to the AA sequence if one base (the 1st G in the 2nd codon) were deleted from the original DNA sequence?

DNA TAC GGC TCT AGC GAG ATA TT

mRNA AUG CCG AGA UCG CUC UAU AA

AA Met Pro Arg Ser Leu Tyr

a. What conclusions can you draw regarding the effect of deletion mutations on the polypeptide chain that would be produced?

There is an incomplete codon because only 2 bases at the end. Frameshift mutation compared to the original strand, every aa after the deletion changes.

b. Do you think that deletion would likely improve or negatively impact the intended function of the

protein produced? Negative impact

29) Substitution mutation - What would happen to the AA produced if a base were substituted for another base in the original DNA strand? (The substituted bases are highlighted below)

DNA TAC CGG CTC TAG CGG GAT ATT

mRNA AUG GCC GAG AUC GCC CUA UAA

AA Met Ala Glu Ile Ala Leu Stop

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a. What can you conclude about the effect of substitution mutations on the polypeptide produced from a strand of DNA?

You can get a complete protein made unlike the other types of point mutations. The amino acid may not even change so the same protein could still be made – having no affect on the organism.

b. Would substitutions improve or negatively impact the intended function of the protein produced? Why? They could negatively impact the function of the protein by changing the amino acid, thereby changing the protein. They could have no impact because the amino acid does not change resulting in the same protein

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