LIFE-102 EXAM 4

What is the double helix?

The double helix is the twisted ladder structure of DNA, made of two strands coiled around each other.

What are Chargaff’s Rules?

In DNA, %A = %T and %C = %G (base pairing consistency).

What is the structure of DNA?

Two strands of nucleotides with a sugar-phosphate backbone and nitrogenous bases (A, T, C, G).

What are base pairing rules?

A pairs with T, C pairs with G

What does “complementary” mean?

Each DNA strand matches the other via base pairing

What does “anti-parallel” mean?

Strands run in opposite directions (5’→3’ and 3’→5’).

What is semiconservative replication?

Each new DNA molecule has one old strand and one new strand.

What are origins of replication?

Specific DNA sequences where replication begins.

What is helicase?

Enzyme that unwinds DNA

What is DNA polymerase?

Enzyme that builds new DNA strands.

What is primase?

Enzyme that lays down RNA primers.

What is ligase?

Enzyme that joins DNA fragments.

What are primers?

Short RNA sequences that start DNA synthesis.

Why are primers necessary?

DNA polymerase cannot start synthesis on its own.

What are Okazaki fragments?

Short DNA pieces made on the lagging strand.

What direction does DNA replication occur?

5’ → 3’

What is the leading strand?

Continuously synthesized strand.

What is the lagging strand?

Discontinuously synthesized strand.

What are telomeres?

Protective ends of chromosomes that prevent DNA loss.

What is the central dogma?

DNA → RNA → Protein

What is the template strand?

DNA strand used to make RNA.

Relationship between DNA and mRNA?

mRNA is complementary to DNA (U replaces T).

What enzyme transcribes DNA into RNA?

RNA polymerase

What happens in transcription initiation?

RNA polymerase binds promoter.

What happens in elongation?

RNA strand is built.

What happens in termination?

RNA polymerase releases RNA.

What is a promoter?

DNA sequence where transcription starts.

What is a terminator?

DNA sequence signaling transcription stop.

What is translation?

Process of making proteins from mRNA.

Role of mRNA?

Carries genetic code.

Role of tRNA?

Brings amino acids to ribosome.

What is the genetic code?

Rules for translating mRNA into protein.

What is a codon?

Three-base mRNA sequence coding for an amino acid.

Why is the genetic code redundant?

Multiple codons can code for the same amino acid.

What is the start codon?

AUG (methionine)

What are stop codons?

UAA, UAG, UGA

What is an anticodon?

tRNA sequence complementary to a codon.

What are introns?

Non-coding regions removed from RNA.

What are exons?

Coding regions kept in RNA.

What is splicing?

Removal of introns and joining of exons.

What is a point mutation?

Change in a single nucleotide.

What is a frameshift mutation?

Insertion/deletion that shifts reading frame.

What is a silent mutation?

No change in amino acid.

What is a missense mutation?

Changes one amino acid.

What is a nonsense mutation?

Creates a stop codon.

Why are viruses acellular?

They are not made of cells.

Steps of viral replication?

Attachment → Entry → Replication → Assembly → Release

What is a capsid?

Protein coat around viral genome.

What is an envelope?

Lipid membrane surrounding some viruses.

What molecules store viral genetic info?

DNA or RNA

What is host range?

Types of cells a virus can infect.

What is tissue tropism?

Specific tissues a virus targets.

Lytic cycle?

Virus replicates and lyses host cell.

Lysogenic cycle?

Viral DNA integrates into host genome.

What is reverse transcriptase?

Enzyme that makes DNA from RNA.

What are prions?

Infectious misfolded proteins.

What are restriction enzymes?

Proteins that cut DNA at specific sequences.

Role of ligase?

Joins DNA fragments.

What is cDNA?

DNA made from mRNA using reverse transcriptase.

What is gel electrophoresis?

Technique to separate DNA by size using electricity.

How does gel electrophoresis work?

Smaller fragments move farther in gel.

What is a nucleic acid probe?

Labeled DNA/RNA used to detect sequences.

What is PCR?

Technique to amplify DNA.

What enzyme is used in PCR?

Taq polymerase

What are cloning vectors?

DNA molecules used to carry foreign DNA.

What are GMOs?

Organisms with altered DNA.

What is gene therapy?

Treatment by inserting genes into cells.

Applications of genetic engineering?

Medicine, agriculture, forensics, research

Thymine (T) makes up 14% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of nucleotides in this sample will be Guanine (G)?

36%

The two strands that make up a molecule of DNA are described as being “antiparallel”. What does this mean?

The 5’ to 3’ direction of one strand runs counter to the 5’ to 3’ direction of the other strand

Because the two strands of a DNA molecule are ________ to each other, either one can be used as a template to reconstruct the other.

Complementary.

After DNA replication is complete, each strand of the original molecule is bound to a newly-synthesized strand. This process is known as

semiconservative replication

During replication, which enzyme unwinds the DNA double helix?

DNA helicase

During DNA replication, each new strand begins with a short __________.

RNA primer

Suppose a new species of bacterium is discovered. It contains a form of DNA polymerase III that can add new nucleotides to either the 5' end or the 3' end of an existing strand. All other properties of the enzyme remain unchanged. How would DNA replication in these bacteria differ from normal replication?

Both new strands could be synthesized continuously like the leading

strand

If a short sequence of DNA is 5' AATTGCCGT 3', its complementary DNA strand’s sequence is __________.

3' TTAACGGCA 5'

The shortening of chromosomes occurs in which types of cells?

Only eukaryotic cells

DNA affects the traits of an organism by providing the instructions for synthesizing _______.

Proteins

During protein synthesis in eukaryotes, which molecule passes from the nucleus to the cytoplasm and specifies the sequence of amino acids in the new polypeptide?

mRNA

During _________, nucleotide sequence information is changed into amino acid sequence information.

Translation

If the sequence of bases in the template strand of a DNA molecule is 3' ATCGCTCC 5', what is the sequence of bases in the RNA that is transcribed from this molecule?

5' UAGCGAGG 3'

Eukaryotic mRNA molecules may contain non-coding sequences that must be removed before translation. These are called __________.

Introns

Anticodons are part of the molecular structure of ___________.

tRNA

The genetic code is redundant. What does this mean?

More than one codon can specify the addition of the same amino acid.

All of the following components listed below are required in order for a gene to be fully-expressed into a protein. Which of the following components is not required during the process of translation?

DNA

Refer to the genetic code. What would the anticodon be for a tRNA that transports Glycine (Gly) to a ribosome?

CCC

The mRNA that codes for a particular eukaryotic protein is shown below:

5’ ACC-AGU-UAA-AUG-UUU-AGA-CUA-GGG-UAG-AAA 3’

What will be the amino acid sequence of this particular protein?

Met-Phe-Arg-Leu-Gly

If the AUG codon shown above in question 19 mutates into AUA, what is the result?

There will not be any of this protein made at all

The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following?

A gene from any organism can theoretically be expressed by any other organism.

Eukaryotic and prokaryotic organisms differ in how they process genetic information. Which statements best explain one of these differences?

In prokaryotes, translation of the mRNA begins before transcription is complete. In eukaryotes, transcription and modification of the mRNA is completed before translation begins.

In a eukaryotic cell, transcription takes place in the __________, and translation takes place in the __________.

Nucleus; Cytosol

Given the sentence "THE FAT CAT ATE THE RED RAT," which of the following would represent a frameshift mutation?

THE FAC ATA TET HER EDR AT

Viruses are self-replicating but the replication is much faster in a host cell.

False

Can a virus be killed?

No, viruses are non-living and cannot die

What best describes whether a virus is likely to infect a particular cell?

A virus will only infect host cells with the correct surface receptors

Your pet cat has just come down with a viral infection that is impacting his upper respiratory tract. What is the most likely reason that your pet dog has not become infected with the same virus?

The host range of the virus does not include dogs.

Retroviruses are unique because they are a combination of RNA and DNA.

False

The direction of genetic information transfer in a retrovirus (such as HIV) is

RNA to DNA to mRNA to protein

Will treating a viral infection with antibiotics affect the course of the infection?

No; antibiotics work by inhibiting enzymes specific to bacteria. Antibiotics have no effect on eukaryotic or virally encoded enzymes.

Prions are

infectious proteins with no associated nucleic acid