7B

Question 1

2. What are the components of DNA and its three-dimensional structure?
   C-3
   S-6

Answer 1

Components: PO4, deoxyribose, nitrogenous base. Structure: double stranded, double helix, antiparallel, twisted ladder, side of sugar and PO4 (backbone), rungs H bonds between nucleotides

Question 2

3. State the Chargaff’s rul

Answer 2

1. The amounts of thymine and adenine in DNA are the same and the amounts of cytosine and guanin are the same (A=T, G=C). 2. The proportion of adenine and gunaine differs among species.

Question 3

4. What evidence enabled Watson and Crick to decipher the structure of DNA?

Answer 3

Rosalind Franklin’s research in x-ray crystallography revealed the shape of DNA molecule: alpha helix. (final piece of evidence.

Question 4

5. Explain how hydrogen bonds contribute to the structure of DNA.

Answer 4

Connect complementary bases forming the “rungs” of the DNA twisted ladder structure. Strengthen DNA.

Question 5

6. Explain the roles of DNA, RNA, and protein in the central dogma.

Answer 5

Gene expression: A multistep process including transcription and translation, by which genetic information encoded by a gene is converted into a structural or functional part of a cell or body. DNA—>transcribed into mRNA—> translated into Protein.

Question 6

7. Describe the structural differences between RNA and DNA.
   4

Answer 6

Single vs. double strand, Uracil instead of Thymine, Ribose vs. Deoxyribose, RNA smaller than DNA.

Question 7

7. Describe the functional differences between RNA and DNA.

Answer 7

DNA: stores RNA/protein encoding information, transfers information to next generation of cells. RNA: carries protein-encoding information, helps to make proteins, catalyzes some reactions.

Question 8

How does mRNA contribute to protein synthesis?

Answer 8

Carries the information that specifies a protein. Has the information in the form of codons (genetic code word that corresponds to one amino acid.)

Question 9

How does rRNA contribute to protein synthesis?

3

Answer 9

Main component of ribosomes where polypeptide chains are built. Correctly aligns ribosome and mRNA, catalyzes the formation of peptide bonds between amino acids.

Question 10

How does tRNA contribute to protein synthesis?

Answer 10

A “connector”, binds an mRNA codon at one end and a specific amino acid at the other. Delivers the amino acid to the ribosome at the correct spot along the mRNA molecule.

Question 11

9. Where in the cell does transcription occur?

Answer 11

Nucleus

Question 12

What is the role of RNA polymerase in transcription?

Answer 12

Def: Enzyme that uses a DNA template to produce a molecule of RNA. (builds the RNA chain) A catalyst!

Question 13

What are the stages of transcription?

Answer 13

Initiation, elongation, termination

Question 14

What happens during the Initiation stage of transcription?

Answer 14

In the Initiation phase, enzymes unzip the DNA double helix exposing the template strand. RNA polymerase then attaches to a promoter (a DNA sequence that signals the gene’s start.)

Question 15

What happens during the Elongaton stage of transcription?

Answer 15

In elongation, RNA polymerase moves over the gene in a 3’ to 5’ direction, unwinds the DNA helix, reads the base sequence, and joins free RNA nucleotides into a complemetary strand of mRNA.

Question 16

What happens during the Termination stage of transcription?

Answer 16

In termination, a terminator sequence signals the end of the gene, and the RNA, DNA and RNA polymerase separate. DNA becomes a double helix again. A RNA copy of a gene has been produced.

Question 17

10. What are the roles of the promoter sequences in transcription?

Answer 17

The promoter is a DNA sequence that signals the gene’s start. It attracts RNA polymerase and transcription factors so transcription can start.

Question 18

10. What are the roles of the terminator sequences in transcription?

Answer 18

The terminator is a DNA sequence that signals where the gene’s coding region ends. Upon reaching the terminator sequence, the RNA polymerase separates from the DNA template and releases the newly sythesized RNA.

Question 19

11. Explain how mRNA is processed after transcription in eukaryotic cells.

Answer 19

Post transcription modification is a process in which eukaryotic cells tailor their RNA before it leaves the nucleus (pre-mRNA to mature mRNA.) After transcription, a sequence of modified nucleotides called a cap is added to the 5’ end of the mRNA. This cap helps mRNA bind to ribosomes. On the 3’ end, adenines are added forming a poly A tail. This tail determines the longevity of the mRNA. In addition, catalytic RNAs and proteins remove the introns from the mRNA. The remaining exons, which will eventaully be expressed, are spliced together. The mature mRNA leaves the nucleus ready to be translated.

Question 20

12. Define Genetic code.

Answer 20

The correspondence between specific nucleotide sequences and amino acids.

Question 21

13. Where in the cell does translation occur?

Answer 21

Cytoplasm

Question 22

What are the sequences of translation?

Answer 22

Initiation, elongation, termination

Question 23

What happens in the Initiation sequence of translation?

Answer 23

An initiation complex is formed. The leader sequence at the 5’ end of the mRNA molecule binds with a small ribosomal subunit. The start codon of the mRNA (AUG) pairs with the anticodon (UAC) of tRNA, which carries the amino acid Methionine. A large ribosomal subunit attaches to the small subunit to complete initiation.

Question 24

What happens in the Elongation sequence of translation?

Answer 24

Carrying a second amino acid, another tRNA molecule’s anticodon binds to the 2nd codon. The first and second amino acids form a covalent (peptide) bond. With the bond in place, the ribosome releases the first tRNA, which can be reused. The ribosome moves down the mRNA by one codon and a 3rd tRNA enters carrying an amino acid. The amino acid bonds to the 2nd amino acid and the polypeptide chain grows. tRNA brings successive amino acids until the ribosome…

Question 25

What happens in the Termination sequence of translation?

Answer 25

The ribosome encounters a stop codon (UGA, UAG, UAA) and polypeptide synthesis ends. tRNA does not bind to the stop codon. Instead, release factors bind to it and the participants of protein synthesis separate. The ribosome releases the last tRNA, the ribosomal subunits separate and are recycled and the new polypeptide is released into the cytoplasm or rough ER.

Question 26

16.  Explain how bacterial cells use operons to regulate gene expression.

Answer 26

An operon is a group of genes plus a promoter and an operator. Lac operon encodes for lactose degrading proteins which allow the bacteria to utilize lactose. If glucose is present or lactose is absent the bacteria does not use lactose and producing the lactose degrading protein would waste energy. So, a repressor protein binds to the operator preventing RNA polymerase from transcribing the genes for the lactose degrading proteins. If the bacteria needs to use lactose, the lactose will bind to the repressor which changes its shape and the repressor detaches from the DNA. RNA polymerase can now transcibe the genes for the lactose degrading protein and the lactose can be utilized.

Question 27

17.  Describe the points at which eukaryotic cells can regulate gene expression in the nucleus.

Answer 27

In the nucleus, gene expression can be regulated in the DNA or mRNA. Transcription factors, activators or repressors, either initiate or inhibit transcription of the DNA. Gene expression can also be regulated the chemical modification of DNA. DNA methylation compresses chromosomes preventing transcription while histone acetylation unravels the chromosome which promotes transcription. In mRNA, alternative splicing mixes up the gene increasing the variety of proteins. mRNA transport inhibits gene expression - if a mRNA got messed up during processing, then it will not be able to leave the nucleus inhibiting expression.

Question 28

17.  Describe the points at which eukaryotic cells can regulate gene expression in the cytoplasm.

Answer 28

In the cytoplasm, the number of poly a tails on mRNA can inhibit protein production. Micro RNA can also be an inhibitor. If too much mRNA is present then micro RNA will chop it up. Protein processing also regulates expression. A protein must fold correctly to be viable, it must get transported to its destination (Golgi, cell membrane). Processed??

Question 29

18.  How can substitution mutations can alter a protein.

Answer 29

Substitution changes the base triplet. In a silent mutation, the substitution encodes for the same protein as the original version (i.e. CCC and CCU both proline.) In a missense mutation, the substituted amino acid may drastically change the shape of the protein which changes the function also (i.e. sickle cell). In a nonsense mutation, a base triplet specifying a protein is changed into one that specifies a stop codon.

Question 30

18.  How can insertion and deletion mutations can alter a protein.

Answer 30

The addition or deletion of one or more nucleotides to a gene. These cause frameshift mutation which disrupt the codon reading frame. A missense mutation alters the amino acid sequence (the cat ate the rate example). A nonsense mution causes stop codons to be either inserted or deleted.