Unit 3: DNA, RNA, Protein synthesis, recombinant DNA

Question 1

DNA and its 3 functions

Answer 1

Deoxyribonucleic acid; the molecule that makes up chromosomes

1. Replicates so that exact copies may be passed to the next generation
2. Mutates to provide variability for evolution
3. Stores information to regulate development and metabolism

Question 2

Nucleotide structure and function

Answer 2

Organic molecule; Serves as the monomer that makes up the polymer DNA/RNA.
Structured with 3 parts: a phosphate group, deoxyribose (5-carbon sugar), and a nitrogenous base.

Question 3

Nucleotide’s nitrogenous base (names and pairing)

Answer 3

Two double ring bases (purines): Adenine (A) and Guanine (G)
Two single ring bases (pyrimidines): Thymine (T) and Cytosine (C)
Pairings: A-T with 2 hydrogen bonds and G-C with 3 hydrogen bonds.

Question 4

DNA structure

Answer 4

Double helix structure of repeating nucleotide units.
When the helix is untied, resembles a ladder. The phosphate group and deoxyribose form the backbone and the nitrogenous bases bind together to make up the middle part of the ladder.
The number, order, as well as the type of bases determine what kind of organism will develop.

Question 5

DNA replication (why? where? semiconservative?)

Answer 5

DNA replication is necessary when a cell divides, as each cell requires an exact copy of DNA. Cell division occurs when the body is growing or healing itself.
DNA replication is called semiconservative because each new DNA is composed of an old (parent) strand and a new (daughter) strand.
DNA replication occurs in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotes

Question 6

DNA replication steps: 1st unwinding (helicase)

Answer 6

DNA becomes untwisted as enzymes break the bonds between nucleotides. The “unzipped” two DNA strands now act as a template for the new DNA molecules. The enzyme that breaks the weak hydrogen bonds which held the nitrogenous bases is called the helicase.

Question 7

DNA replication steps: 2nd pairing (DNA polymerase)

Answer 7

New nucleotides from the nucleus move into place and pairs with the complementary bases on the two exposed strands. Enzyme called DNA polymerase assists with the pairing by positioning the incoming nucleotides as well as making sure the correct nucleotides are in place. (Remember, A-T and G-C)

Question 8

DNA replication steps: 3rd joining (ligase)

Answer 8

The adjacent nucleotides join together to form a new chain. Enzyme called ligase seals any breaks in the alternating sugar-phosphate backbone.

Question 9

RNA structure and comparison to DNA

Answer 9

RNA contains the sugar ribose, instead of deoxyribose. The bases are A, C, G, and instead of thymine, it is Uracil (U). RNA is also single stranded and does not form a helix.

Question 10

Types of RNA

Answer 10

• mRNA: messenger RNA; linear structure
• tRNA: transfer RNA; folded structure
• rRNA: ribosomal RNA; globular structure

Question 11

Recombinant DNA (rDNA) (what do you need to make rDNA)

Answer 11

DNA with genes from 2 or more different organisms. Often produced in the laboratory by introducing foreign genes into a bacterial plasmid.
Need:
-a vector, a piece of DNA that can be manipulated
-a plasmid, a small ring of DNA from bacteria that is not part of its chromosome and capable of replicating on their own
-restriction enzyme
-ligase

Question 12

Formation of insulin rDNA (4 steps)

Answer 12

1. Restriction enzyme cleaves both the plasmid DNA as well as the human DNA to extract the insulin gene
2. Ligase seals human gene and plasmid, now forming the recombinant DNA.
3. The host cell, in this case bacteria, take up the recombined plasmid
4. As the cell reproduces itself, multiple cloned insulin gene is made

Question 13

Benefits of rDNA

Answer 13

• Bacteria containing rDNA used to produce human products (insulin, human growth hormone, etc)
• Production of vaccines
• Diagnostic tool to identify diseases
• DNA fingerprinting
• Produce plants that are disease resistant
• Gene mapping

Question 14

DNA & protein (Gene)

Answer 14

DNA is the master copy of instructions for the production of proteins.
Gene: Segment of DNA that contains the genetic information necessary to produce protein

Question 15

Why are messenger RNAs necessary?

Answer 15

Proteins are made in the cytoplasm, but DNA is bounded in the nucleus. Thus, there has to be some kind of mechanism to get the message from DNA to the site of protein synthesis.
This mechanism is done with the aid of a messenger molecule called messenger RNA.

Question 16

Triplet code (codon)

Answer 16

Every 3 nitrogenous bases in a DNA strand accounts for ONE amino acid. Once the code is transcribed onto mRNA, each 3 base set is called a codon.

Question 17

Protein synthesis: Transcription (6 steps) include enzymes helicase, RNA polymerase, and ligase

Answer 17

1. The gene codes in DNA for the protein that will be produced is selected, isolated, and uncoiled by the enzyme helicase. The hydrogen bond between the DNA base pairs is broken to provide the DNA template.
2. Floating RNA nucleotides join the appropriate base pairs of the DNA template with the help of the enzyme RNA polymerase. Uracil base of RNA always joins to adenine of the DNA
3. The enzyme ligase glues the sugar-phosphate backbone of the mRNA together.
4. Enzymes break the temporarily formed hydrogen bond between the newly produced mRNA molecule and the DNA template, releasing the mRNA; we now have a mRNA strand.
5. DNA molecules join back together; mRNA is processed in the nucleus before passing through the nuclear pores into the cytoplasm.
6. DNA coils back up into its double helix shape with the help of enzymes.

Question 18

Transfer RNA function (anticodon)

Answer 18

Molecules that bring amino acids to the ribosomes. tRNA contains a set of 3 bases called the anticodon which match with the 3 bases on the mRNA strand. (if codon is AUG, the anticodon is UAC)

Question 19

What is AUG? Which amino acid corresponds to AUG?

Answer 19

AUG is the most common start codon of mRNAs. Methionine is therefore the first amino acid incorporated into proteins.

Question 20

Protein synthesis: Translation 1st step chain initiation

Answer 20

i) Small ribosomal unit attaches to the mRNA near the start codon AUG.
ii) The anticodon of the initiator tRNA with methionine pairs with the codon AUG
iii) the large ribosomal subunit joins to the small subunit.

Question 21

Protein synthesis: Translation 2nd step chain elongation (translocation)

Answer 21

A ribosome has two binding sites for tRNA.

i) A new tRNA arrives and joins the second binding site. The amino acid (or polypeptide; if this process has been going on) from the tRNA of the first binding site is joined by peptide bonds to the amino acid of the new tRNA.
ii) the first tRNA is released, and the ribosome moves forward one codon. (now the new tRNA is in the first binding spot). This movement of ribosome is called translocation.

Question 22

Protein synthesis: Translation 3rd step chain termination

Answer 22

Termination occurs at one of the three stop codons, which does not code for any amino acid.

i) A release factor binds to the ribosome and the polypeptide is enzymatically cut from the last tRNA.
ii) tRNA and polypeptide leaves the ribosome. The ribosome breaks down into its two subunits.

Question 23

Gene mutation and its 3 causes (examples of mutagens)

Answer 23

A change in the sequence of bases within a gene

1. Errors in Replication: Very rare; as the enzyme DNA polymerase prevents mismatched DNA strands.
2. Mutagens: Environmental influences that cause mutations. i.e., radiation (X-rays, UV radiation) and certain organic chemicals (chemicals in cigarette smoke).
3. Transposons: Specific DNA sequences that are able to move within and between chromosomes. Their movement may alter neighboring genes.

Question 24

Frameshift mutation

Answer 24

Type of gene mutation
When one or more nucleotide is either inserted or deleted from DNA, resulting in a polypeptide that codes for the wrong sequence of amino acids.

Question 25

Point mutation (3 types)

Answer 25

Point mutation: A replacement of a single nitrogen base in DNA with another.

i) silent mutation: When the replacement of a base produces a codon that creates the same amino acid as before (no change) i.e., UAC is changed to UAU, both are code for tyrosine.
ii) nonsense mutation: When the replacement of a base produces a stop codon. i.e., UAC is changed to UAG, a stop codon
iii) missense mutation: When the replacement of a base produces a codon that creates a different amino acid.