Nucleic Acids Flashcards
1
Q
Two Types of Nucleic Acids:
A
1- DNA: Deoxyribonucleic Acid: Found within cell nucleus
Storage and transfer of genetic information
Passed from one cell to other during cell division
2- RNA: Ribonucleic Acid: Occurs in all parts of cell
Primary function is to synthesize the proteins
2
Q
Polymers in which repeating unit is nucleotide
A
Nucleic Acids
3
Q
A Nucleotide has three components:
A
Pentose Sugar
Phosphate Group (PO43-)
Nitrogenous Base
4
Q
Structural difference between Pentose Sugars ribose or 2-deoxyribose
A
OH group present on carbon 2’ in ribose
H atom in 2-deoxyribose
5
Q
pyrimidine
A
thymine (T), cytosine (C), and uracil (U)
6
Q
pyrimidine
A
thymine (T), cytosine (C), and uracil (U)
7
Q
purine
A
adenine (A) and guanine (G)
8
Q
Nucleotide units are linked through phosphate and sugar bonds called….
A
phosphodiester bonds
9
Q
Sugar-phosphate groups are referred to as nucleic acid——
A
backbone
10
Q
Sugar-phosphate groups are referred to as nucleic acid——
A
backbone
11
Q
Backbone in Nucleic acids
A
Phospahate-Sugar
12
Q
Backbone in proteins
A
Peptide bonds
13
Q
Nucleic acids have ——— and ——– structure
A
secondary and tertiary
14
Q
Weak Forces Stabilize the Double Helix
A
(1) Hydrophobic effects.
(2) Stacking interactions.
(3) Hydrogen bonds.
(4) Charge-charge interactions.
15
Q
————- enzymes that can alter the topology of DNA helixes by:
(1)
(2)
(3)
A
Topoisomerases
(1) Cleaving one or both DNA strands
(2) Unwinding or overwinding the double helix by rotating the strands
(3) Rejoining ends to create (or remove) supercoils
16
Q
DNA is complexed with proteins (———) to form chromatin material (————).
A
histones
chromosomes
17
Q
————–DNA plus various proteins that package the DNA in a more compact form
A
Chromatin
18
Q
————–DNA plus various proteins that package the DNA in a more compact form
A
Chromatin
19
Q
Histones
A
the major proteins of chromatin
Eukaryotes contain five small, basic histone proteins containing many lysines and arginines: H1, H2A, H2B, H3, and H4
Positively charged histones bind to negatively-charged sugar-phosphates of DNA
20
Q
———– are DNA-histone complexes on a “string” of double-stranded DNA
A
Nucleosome
21
Q
Each nucleosome is composed of:
A
Histone H1(1 molecule) Histones H2A, H2B, H3, H4 (2 molecules each)
~200 bp of DNA
22
Q
Replication
A
Process by which DNA molecules produce exact duplicates of themselves
Old strands act as templates for the synthesis of new strands
The newly synthesized DNA has one new DNA strand and old DNA strand
23
Q
Enzymes that checks the correct base pairing and catalyses the formation of phosphodiester linkages
and can only function in the 5’-to-3’ direction
A
DNA polymerase
24
Q
———– grows continuously in the direction of unwinding
The ———- grows in segments (Okazaki fragments) in the opposite direction
A
leading strand
lagging strand
25
chromosomes have similar, but not identical, DNA base sequences
Homologous chromosomes
Both code for the same traits (genes) but for different forms of the trait (genes)
Example - blue eyes versus brown eyes.
26
Proteins are responsible for the formation of
skin, hair, enzymes, hormones, and so on
27
Protein synthesis can be divided into two phases.
Transcription – synthesis of messenger RNA
Translation – ribosomal protein synthesis
28
Types of RNA molecules
- Heterogeneous nuclear RNA (hnRNA)
- Messenger RNA
- Small nuclear RNA
- Ribosomal RNA (rRNA)
- Transfer RNA (tRNA)
29
Transcription
A process by which DNA directs the synthesis of mRNA molecules
Two-step process - (1) synthesis of hnRNA and (2) editing to yield mRNA molecule
30
Gene
A segment of a DNA base sequence responsible for the production of a specific hnRNA/mRNA molecule
Most human genes are ~1000–3500 nucleotide units long
31
Genome
All of the genetic material (the total DNA) contained in the chromosomes of an organism
Human genome is about 20,000–25,000 genes
32
Steps in the Transcription Process
1- Unwinding of DNA double helix to expose some bases (a gene)
The unwinding process is governed by RNA polymerase
2- Alignment of free ribonucleotides along the exposed DNA strand (template) forming new base pairs
3- RNA polymerase catalyzes the linkage of ribonucleotides one by one to form mRNA molecule
4- Transcription ends when the RNA polymerase enzyme encounters a stop signal on the DNA template
The newly formed RNA molecule and the RNA polymerase enzyme are released
33
Post-Transcription Processing: Formation of mRNA
Involves conversion of hnRNA to mRNA
- Splicing
- Alternative splicing
34
Excision of introns and joining of exons
Splicing
35
A process by which several different protein variants are produced from a single gene
Alternative splicing
36
Characteristics of genetic code:
- The genetic code is highly degenerate
- There is a pattern to the arrangement of synonyms in the genetic code table.
- The genetic code is almost universal
- An initiation codon exists
37
Two important features of the tRNA structure
1. The 3 end of tRNA is where an amino acid is covalently bonded to the tRNA
2. The loop opposite to the open end of tRNA is the site for a sequence of three bases called an anticodon
38
Translation
a process in which mRNA codons are deciphered to synthesize a protein molecule
39
rRNA–protein complex - serves as the site of protein synthesis
Ribosome
40
There are five general steps to the translation process:
1) Activation of tRNA,
2) Initiation,
3) Elongation,
4) Termination, and
5) Post-translational processing.
Activation of tRNA: addition of specific amino acids to the 3’-OH group of tRNA
41
Termination
The polypeptide continues to grow via translocation until all necessary amino acids are in place and bonded to each other.
Appearance of one of three stop codons (UAA, UAG, or UGA) in the A-site of the ribosome terminates the process because no tRNA has an anticodon that can base-pair with these stop codons.
This leads to cleavage of polypeptide from the tRNA through hydrolysis
42
Post-translational processing
gives the protein the final form it needs to be fully functional
- (Met) residue is removed by hydrolysis
- covalent modifications include formation of disulfide bridges between cysteine residues
Allows for proper folding of proteins
43
----------- releases the polypeptide chain from its tRNA carrier
Hydrolysis
44
polysomes
several ribosomes bind to a single mRNA
45
Which of the following is a major function of nucleic acids?
A) storage and transfer of genetic information
B) storage and intracellular transfer of energy
C) catalysis of virtually all biochemical reactions
D) structural support in both plants and animals
E) long term storage of energy
A) storage and transfer of genetic information
46
Chromatin is
A) nuclear material composed of DNA and histones.
B) the portion of a chromosome that codes for a specific trait.
C) a protein found on the surface of a cell.
D) the fluid part of a cell that surrounds the organelles.
E) a component of cell membranes.
A) nuclear material composed of DNA and histones.
47
DNA is primarily located in what part of the cell?
A) cytoplasm
B) mitochondrion
C) nucleus
D) ribosome
E) cell membrane
C) nucleus
48
What is the repeating unit in nucleic acids?
A) monosaccharides
B) amino acids
C) nucleotides
D) nucleosides
E) nitrogen bases
C) nucleotides
49
The chemical combination of ribose and one of the five nitrogen bases results in formation of a
A) nucleotide.
B) nucleoside.
C) DNA molecule.
D) chromosome.
E) gene.
B) nucleoside.
50
When a β-N-glycosidic bond forms between guanine and deoxyribose, the resulting
molecule is called
A) riboguanine.
B) deoxyriboguanine.
C) deoxyriboguanosine.
D) guanosine.
E) deoxyguanidine.
C) deoxyriboguanosine.
51
A chromosome is a(an)
A) complex of DNA and histones formed in a cell nucleus before cell division.
B) segment of DNA that directs synthesis of a specific peptide or protein.
C) list of locations of markers that relate to inheritable traits.
D) set of identical copies of DNA segments from a single ancestor.
E) ordered list of the nucleotides in a segment of DNA.
A) complex of DNA and histones formed in a cell nucleus before cell division.
52
A nucleotide is composed of a ________ with a ________ added to it.
A) pentose; phosphate group
B) pentose; nitrogen base
C) nucleoside; nitrogen base
D) nucleoside; phosphate group
E) phosphate group; nitrogen base
D) nucleoside; phosphate group
53
A nucleotide is a(an)
A) amide of a nitrogen base and a fatty acid.
B) amide of a nucleoside and a fatty acid.
C) ester of a nucleoside and a fatty acid.
D) 5'-monophosphate ester of a nucleoside.
E) polymer of alternating ribose and purine or pyrimidine units.
D) 5'-monophosphate ester of a nucleoside
54
All of the following are components of nucleotides except
A) aldopentoses in the form of five-membered rings.
B) heterocyclic nitrogen bases consisting of six-membered rings.
C) heterocyclic nitrogen bases consisting of two fused rings.
D) phosphate group
E) metal ions.
E) metal ions.
55
Which base is normally found in RNA but not in DNA?
A) thymine
B) adenine
C) guanine
D) uracil
E) cytosine
D) uracil
56
Which base is normally found in DNA but not in RNA?
A) thymine
B) adenine
C) guanine
D) uracil
E) cytosine
A) thymine
57
Which of the following is a nitrogen base found in nucleic acids?
A) thymidine
B) adenine
C) guanosine
D) pyridine
E) ammonia
B) adenine
58
Which of the following is a nucleoside which would be found in DNA?
A) adenosine triphosphate
B) UMP
C) deoxyguanosine
D) deoxyribose
E) deoxythymidine diphosphate
C) deoxyguanosine
59
The most characteristic feature of all the bases found in either DNA or RNA is ________.
A) they are all nitrogen containing aromatic compounds.
B) they are all six membered rings
C) they are all fused five and six membered rings
D) they all bond to the sugar ring through the number 1 carbon of the base
E) they all have at least one corbonyl group attached to the six-membered ring
A) they are all nitrogen containing aromatic compounds.
60
The purine bases are
A) fused 5 and 6 membered ring systems containing 4 ring nitrogens.
B) 6 membered ring systems containing 2 ring nitrogens.
C) 6 membered ring systems containing 4 ring nitrogens.
D) fused 5 and 6 membered ring systems containing 2 nitrogens.
E) none of the above
A) fused 5 and 6 membered ring systems containing 4 ring nitrogens.
61
The pyrimidine bases are
A) 6 membered ring systems containing 2 ring nitrogens.
B) fused 5 and 6 membered ring systems containing 4 ring nitrogens.
C) 6 membered ring systems containing 4 ring nitrogens.
D) fused 5 and 6 membered ring systems containing 2 nitrogens.
E) none of the above.
A) 6 membered ring systems containing 2 ring nitrogens.
62
The sugar found in an RNA nucleotide is ________.
A) D-ribose
B) 2-deoxy-D-ribose
C) D-rhamnose
D) D-raffinose
E) all of the above
A) D-ribose
63
The backbone of a nucleic acid molecule consists of
A) alternating sugar and phosphate groups linked by phosphate ester bonds.
B) alternating sugar and nitrogen base groups linked by amide bonds.
C) alternating nitrogen bases and phosphate groups linked by amide bonds and
4
strengthened by hydrogen bonds.
D) sugar molecules bonded from the #3 carbon of one molecule to the #5 carbon of the
other by glycosidic linkages.
E) complementary bases joined by hydrogen bonds.
A) alternating sugar and phosphate groups linked by phosphate ester bonds.
64
Which statement does not correctly describe structural differences between DNA and RNA?
A) RNA contains uracil instead of thymine.
B) RNA molecules have a lower molecular mass than DNA molecules.
C) RNA molecules are generally single-stranded.
D) The sugar in RNA has one more hydroxyl group than the sugar in DNA.
E) All of the statements are correct.
E) All of the statements are correct.
65
In a molecule of DNA, the sugar of one nucleotide binds through its ________ hydroxyl
group to the ________ hydroxyl group of the next nucleotide by forming a phosphate ester.
A) 3', 5'
B) 3', 3'
C) 5', 5'
D) 1', 3'
E) 1', 5'
A) 3', 5'
66
The number of hydrogen bonds between adenine and thymine in DNA is ________.
A) 0
B) 1
C) 2
D) 3
E) 4
C) 2
67
The number of hydrogen bonds between cytosine and guanine in DNA is ________.
A) 0
B) 1
C) 2
D) 3
E) 4
D) 3
68
One pair of nitrogen bases in DNA is
A) adenine and thymine.
B) adenine and guanine.
C) adenine and uracil.
D) adenine and cytosine.
E) none of the above
A) adenine and thymine.
69
One pair of nitrogen bases in DNA is
A) guanine and adenine.
B) guanine and thymine.
C) guanine and cytosine.
D) guanine and uracil.
E) none of the above
C) guanine and cytosine
70
The number of hydrogen bonds between guanine and adenine in DNA is ________.
A) 0
B) 1
C) 2
D) 3
E) 4
A) 0
71
In DNA, a DNA sequence complementary to the strand shown below is
C-G-G-T-T-A-G
A) G-C-C-A-A-T-C.
B) C-G-G-T-T-A-G.
C) A-T-T-G-G-C-T.
D) G-C-C-U-U-U-C.
E) G-C-C-U-U-A-C.
A) G-C-C-A-A-T-C.
72
What is the complementary strand for a single DNA strand with the sequence TCGA?
A) TGCA
B) AGCT
C) CTAC
D) GATC
E) TCGA
B) AGCT
73
The number of hydrogen bonds between cytosine and thymine in DNA is ________.
A) 0
B) 1
C) 2
D) 3
E) 4
A) 0
