Unit 4: DNA and the Central Dogma of Biology

Unit 4: DNA and the Central Dogma of Biology

—-----------------------------------------------------------------------------------------------------

1. Chromosomes and Genes

1. What are chromosomes?

• DNA wrapped around proteins called histones 

2. Where are chromosomes found?

• In the nucleus

3. What are sections of DNA called?

• Genes

4. What are identical copies of chromosomes called?

• Chromatids 

5. What holds chromatids together 

• Centromeres

6. What is the difference between eukaryotic and prokaryotic chromosomes?

• In prokaryotes, the circular chromosome is contained in the cytoplasm in an area called the nucleoid. In contrast, in eukaryotes, all of the cell's chromosomes are stored inside a structure called the nucleus.

II. History of DNA

1. Who is Erwin Chargaff?

• A chemist who developed Chargaff’s rules

2. What did Chargaff’s rules state?

• That the bases of DNA are paired together in a specific order (Adenine (A) pairs with Thymine (T); A=T, T=A / Cytosine (C) pairs with Guanine (G); C=G, G=C / The percentage of a bases sample is equal to its pair; i.e. 32% of Guanine = 32% of Cytosine and that equals 64% so that means both Adenine and Thymine are both 18% and a DNA sample has to equal 100%

3. Who is Rosalind Franklin?

• A British female scientist who made a huge contribution to the study of DNA by establishing that it existed in a spiral three-dimensional shape with the use of X-ray diffraction

4. What is the most famous x-ray image of DNA that was taken by Rosalind Franklin in 1952?

• Photo 51

5. How long did it take to get the image and how long did it take to do the calculations for the image 

• 100 hours / 1 year

6. Who was Rosalind Franklin’s boss?

• Maurice Wilkins

7. Who saw her photograph on her desk while attending one of her seminars and built the structures of DNA based on this famous photo which lead to the creation of the first DNA model?

• Watson and Crick

8. Who created the first accurate DNA model with the help of Chargaff and Franklin’s research?

• James Watson and Francis Crick

9. What was the structure they created?

• A double helix with the sides consisting of subunits called nucleotides

10. What does a DNA nucleotide consist of?

• The sugar: Deoxyribose, a phosphate, and a nitrogen base

11. What are the sides of the double helix?

• The alternating sugar and phosphate “backbone”

12.  What are the rungs of the “ladder”?

• Paired nitrogenous bases

13. What holds the two sides together and twists it into the Double Helix Shape?

• Hydrogen bonds

14. How many hydrogen bonds are between the nitrogenous bases?

• Between A and T there are 2 hydrogen bonds

• Between G and C there are 3 hydrogen bonds

15. What types of bonds are hydrogen bonds?

• Weak bonds

16. When are hydrogen bonds helpful?

• During DNA replication

17. Who’s experiments proved that DNA is the molecule for genetics?

• Frederick Griffth’s

18. What was Griffith searching for in this experiment originally?

• A vaccine to two varieties of streptococcus.

19. What were the two varieties?

• One variety of bacteria that had a capsule (like a cell wall) and another without a capsule

20. What was Part 1 of his experiment?

• He injected mice with live encapsulated bacteria which resulted in the mice contracting pneumonia and dying (expected result)

21. What was Part 2 of his experiment?

• He injected mice with live bacteria that had no capsule which resulted in the mice living and their immune system destroying the bacteria (expected result)

22. What was Part 3 of his experiment?

• He injected mice with heat killed encapsulated bacteria which resulted in the mice remaining healthy (expected result)

23. What was Part 4 of his experiment?

• He injected mice with dead encapsulated bacteria and non capsulated bacteria which resulted in the mice contracting pneumonia and dying (unexpected result)

24. How did the mice end up dying?

• The live non capsulated bacteria went through DNA transformation and now they can make a capsule

III. DNA Structure 

1. What is a nucleic acid that is present in ALL living cells?

• DNA (Deoxyribonucleic Acid)

2. What does the DNA molecule contain?

• ALL of the instructions that determine the traits a living organism needs to survive

• It act as a Million Dollar “blueprint” for living organisms

3. What is the length of DNA that almost every cell in the human body has?

• 2 meters of DNA

4. What does DNA give each organism?

• Its unique characteristics

5. What does a DNA nucleotide consist of?

• Sugar deoxyribose, a phosphate, and a nitrogenous base

6. How many strands does DNA have

• 2

• Its double stranded

7. What is DNA often coiled around?

• Proteins called histones

8. Except for being sections of DNA, what is another definition for genes?

• Genes are segments of nucleotides located on the chromosomes that give specific instructions for a certain trait

9. What do DNA chromosomes in prokaryotes form?

• Loose loops within the cell’s cytoplasm

10. As prokaryotes do NOT have a nucleus, where is the DNA loop located?

• The DNA loop is in a part of the cell called the nucleoid region

11. What does the suffix “old” mean and what does it imply?

• “Like”/ that it is like the nucleus because that is where the DNA is found

IV. RNA Structure

1. What is RNA (Ribonucleic Acid)?

• A mirror copy of a segment of DNA (a gene), which then ma be delivered to the ribosome to be converted into a protein

• (A ribosome is  the cellular machinery responsible for making proteins)

2. What on the RNA determines the order of amino acids that will build certain proteins

• The order of the bases on the RNA

3. What are proteins?

• Molecules made up of amino acids that are needed to build and repair body structures.

• They also regulate body processes

• They do ALL their work within the cell

4. What can RNA also make?

• Structures, such as ribosomes (rRNA) and Transfer rna molecules (tRNA)

5. What is the sugar in RNA called?

• Ribose

6. What is Thymine replaced by in RNA)

• The nucleotide Uracil 

7. What is the difference between Thymine and Uracil?

• Uracil has a structure that allows it to leave the nucleus; whereas Thymine cannot leave the nucleus because of its structure

8. What do you follow when pairing the bases of RNA?

• Chargoff’s rules

• (A is now paired with U / C and G are still paired together)

9. How many strands does RNA have?

• One

• RNA is only a single sided strand

V. DNA Replication and Transcription

1. What is a dogma?

• Something that stays the same

2. What is the Dogma of Biology

• How proteins are made within cells and how they stay the same in every single cells

3. What is DNA replication?

• The process by which DNA makes a copy of itself

4. What is the first step to DNA replication?

• A DNA helicase (enzyme) unwinds the DNA.

5. What is the junction (the place where the strands split) between the strands called?

• The replication fork

6. What is DNA polymerase?

• An enzyme that creates DNA by adding nucleotides that pair.

• DNA polymerase “reads” the existing DNA strands to create two new strands that match the existing ones.

7. What is the second step to DNA replication?

• DNA polymerase adds the complementary nucleotides and bins the sugars and phosphates. 

• DNA polymerase travels from the 3’ to the 5’ end.

8. What is the original strand of DNA in a new DNA double helix called?

• Semi conservative

9. What is the third step to DNA replication?

• DNA polymerase adds complementary nucleotides on the other side of the ladder while traveling in the opposite direction

10. What are both sides of the double helix split into?

• The leading strand and the lagging strand 

11. What is the leading strand?

• The side of a DNA molecule, that has been split, that follows the helicase as it unwinds

12. What is the lagging strand?

• The side of a DNA molecule that, that has been split, that moves away from the helicase (in the 5’ to 3’ direction)

13. What is replication called?

• Semi - conservative

14. Why?

• Because one half of the original strand is always saved, or “conserved”

15. What is the problem created during DNA replication?

• It reaches the replication fork, but the helicase is moving in the opposite direction It stops, and another polymerase binds farther down the chain

16. What does this process create?

• Several fragments, called Okazaki Fragments, that are bound together by DNA ligase.

17. What is being synthesized at the same time during replication?

• Many points along DNA

18. Why are multiple points opened up at the same time?

• It would take forever to go from one end to the other

• It is more efficient to open up several points at one time

19. What does transcription mean?

• The process of making a working copy of an original

20. What is transcription the first step of?

• Making a protein

21. How does transcription begin?

• By making a mirror copy of a gene on the DNA strand in the nucleus.

22. What is this copied gene called?

• Messenger RNA (mRNA)

23. Where does mRNA move once it is created?

• It moves through the nuclear membrane to a ribosome to synthesize a specific protein

24. What do primer’s do?

• It tells where the DNA polymers go. 

VI. Translation

1. Where does mRNA travel once it is made? (pretty much same as previous question)

• Outside of the nucleus to a ribosome (protein factory)

2. What has to happen to mRNA?

• It has to be translated by a molecule called transfer RNA (tRNA)

3. How does tRNA work

• Like a translator from English to SPanish or vice versa; the tRNA has to read the code on the mRNA and pair it with the appropriate amino acid it interprets for.

4. How is mRNA fed through the ribosome?

• Like a ribbon, three at a time

5. What are three nitrogenous bases grouped together called?

• A codon 

6. What is the code for one amino acid?

• Three bases (a codon) on the RNA

7. What does This create?

•  diversity in life

8.  what is diversity

•  the differences of a sequence of amino acids that combine to make a protein

9. whatt is the job of TRNA 

• To bring amino acids from inside the cell to make the protein 

10.  Where do these amino acids come from

•  from the foods (protein) that we eat and have been broken down by digestive system and delivered to the cells through the circulatory and cardiovascular systems 

11. What is the basic building block of a protein 

•  an amino acid

12. When do amino acids chemically combine together?

• When the tRNA matches the three base codes on the mRNA 

• If the base code on the mRNA is ACG, the complementary base codes on the tRNA need to be used UGC to deliver and correct amino acid…. in this codon’s case it is cytosine

13. What are the codes that are on the TRNA and complement the MRNA called?

•  Anticodons

14.  What does the growing chain of amino acids become?

•  the desired protein

VIII. Mutations

1. What is a mutation? 

•  a change in the nucleotide-base sequence of a gene

2.  Why are mutations caused by?

•  mutagens

3.  What is a mutagen?

•  any physical or chemical agent that changes the DNA sequence

4.  what are the six examples of mutagens

•  ultraviolet radiation (UV radiation) from the Sun, cigarette smoke, alcohol in excess, viruses, car exhaust, chemicals (laboratory, pesticides, insecticides poisons) 

5. What are the six types of chromosomal mutations

•  Deletions = a base is left out of the “copying”

•  Insertion =  a base pair is added during the “copying”

•  Substitution =  a base pair is replaced during the “copying”

•  Translocation =  a part of one chromosome breaks off and attaches to another

•  Duplication =  produces an extra copy of all or part of a  if the mutation occurs in the part of the DNA sequence that is not in control of that particular solar function chromosome 

• Inversion =  reverses the direction of parts of a chromosome

6.  What is an example of a substitution mutation?

•  for example, with sickle cell anemia and a is replaced with a t ( The amino acid changes from glutamic acid to valine.. look at your codon chart)

7.  what are the three types of gene mutations

•  point mutation -  substitute one base for ( original:  A T A C A C → Mutant: T T A C A C

•  frameshift mutation -  a base is either added or removed which causes a shift in the reading frame.  Many genes are affected. (Original: A T A C A C A A G C C A → Mutant: A T T A C A C A A G C C A) 

•  silent mutation -  a base is changed but the resulting amino acid is the same as in the non-mutant DNA.  no outward changes ((Original: A A A C A G→ Mutant:A A G C A G)

•  nonsense mutation -  a codon is changed to stop a codon (Original:A T A C C C A A A → Mutant:A T T C C C A A A)

8. What are the three possible consequences to a mutation?

•  An “improved” trait occurs i.e. This mutation may help the organism survive in the changing environment

•  a “no change” in a trait occurs i.e. If the mutation occurs and the part of the DNA sequence that is not in control of the particular cellular function, there will be no problem.

•  a “harmful trait” occurs i.e.  The mutation occurs in the sequence of DNA that does control the cell's function and the organism may have some disability or defect.

9. What do cells make that detect e mutations and try to correct the mistake?

•  proteins

10. When an error is found, it is corrected ,but occasionally the error, if not fixed correctly, may become part of the organisms what?

• Genetic makeup

11. Where must a mutation occur for it to be passed from one generation to the next?

• In the gametes (sperm or egg)

12. Most people have some genetic mutations as a part of their own genetic makeup. Why do they not affect us too much?

- They're not all harmful