Macromolecules of the Cell - Nucleic Acids, Structure & Function Flashcards
What does DNA stand for?
DeoxyriboNucleic Acid.
The main role of DNA in the cell is the long-term storage of …………….. .
Information.
All known cellular life and all known viruses contain DNA - true or false?
False. All known cellular life does contain DNA, but only some viruses contain DNA.
In vertebrates, which cells do not contain DNA, because their nuclei are lost when the cells are made?
Erythrocytes (red blood cells).
What are the five nitrogenous bases found in DNA?
Cytosine, thymine, uracil (in RNA), adenine and guanine.
What are the two categories of nitrogenous bases? What are the differences between the two?
Pyramidines - one ring in the atom.
Purines - two rings in the atom.
Name the three pyramidine nitrogenous bases.
Hint: CUt The PYe!
Cytosine, uracil and thymine.
Name the two purine nitrogenous bases.
Hint: PURe As Gold!
Adenine and guanine.
Besides the nitrogenous base, what are the two other components of DNA?
Phosphate and deoxyribose.
Deoxyribose is a …………. sugar with … -group on the second carbon atom.
Pentose, hydrogen.
A nitrogenous base linked to a sugar is known as a ……………. ?
Nucleoside.
What sort of linkages join nitrogenous bases to deoxyribose in a nucleoside?
N-glycosidic linkages.
Which carbon of deoxyribose is a nitrogenous base bonded to with an n-glycosidic linkage in a nucleoside?
C 1’.
Where are phosphates added to nucleosides to form nucleotides?
At C 5’ of the sugar (top of the pentagon).
Name some biochemical uses of nucleotides.
- Chemical energy - ATP is a nucleotide.
- It is a product of phosphorylation and cellular respiration.
- Used in motility and cell division.
- Signal transduction pathways and secondary messenger systems.
In the DNA structure, the two strands run antiparallel - what does this mean?
They run in opposite directions - one from the 5’ to the 3’ end and one from the 3’ to the 5’ end.
True or false? One strand of DNA has purines (adenine and guanine), the other side has pyramidines (thymine and cytosine).
True.
Which DNA bases always pair together?
Adenine / thymine.
Cytosine / guanine.
How many hydrogen bonds are there between adenine and thymine?
Two.
How many hydrogen bonds are there between cytosine and guanine?
Three.
What implications does the difference in the number of hydrogen bonds between adenine and thymine (two) and cytosine and guanine (three) have?
Although the H-bonds are relatively easy to break, it is slightly easier to break the two bonds between adenine and thymine than it is to break the three bonds between cytosine and guanine.
By convention, DNA base pairs are always written from which end?
From the 5’ end to the 3’ end.
True or false? Watson and Crick’s 1953 paper was the first time genes and DNA were known about?
False. They discovered DNA’s double helix structure, but genes and DNA were alreaday known about prior to 1953.
What is the minor groove and the major groove?
The minor groove is where the turns of the DNA doube helix are closer together; the major groove is where they are further apart.
What is being described here?
Formed from DNA and protein, they resemble ‘beads on a string’ when viewed under an electron microscope.
The ‘beads’ are nucleosomes made of DNA wrapped around a protein core.
Chromatin.
What is Chargraff’s First Rule?
That in any dsDNA molecule, the amount of guanine equals the amount of cytosine and the amount of adenine equals the amount of thymine.
Are there always equal amounts of cytosine / guanine to adenine / thymine in a dsDNA molecule?
Not necessarily, no.
What happens if a dsDNA molecule has a higher proportion of cytosine / guanine than of adenine / thymine?
It is more difficult to pull apart because there are more of the triple hydrogen bonds that hold cytosine and guanine together.
As genomes, DNA can take three forms - name them.
- Single stranded DNA (ssDNA). Found in some viruses.
- Double stranded loop (dsDNA). In bacteria, viruses, mitochondria and chloroplasts.
- Double stranded linear (dsDNA). In most eukaryotic cells.
True or false - the size and complexity of an organism depends on the number of genes that it has. The bigger and more complex the organism, the more chromosomes there are in its genome.
False. The size and complexity of an animal has no bearing on the number of chromosomes it has.
What is DNA complexed with to form nucleosomes, the next level of chromosome structure?
Histones. Each nucleosome consists of eight histone proteins. The DNA wraps around these 1.65 times.
What is a chromatosome formed of?
A nucleosome plus the H1 histone.
Chromatosomes are folded, looped, compressed and tightly coiled to form the tightly condensed DNA in a ……………. ?
Chromatid.
Put the levels of chromosome structure in the correct order:
Histone
Nucleosome
Chromatosome
Chromosome
Chromatin
H1 Histone
Chromatid.
- Chromatin.
- Histone + nucleosome.
- Nucleosome + H1 histone.
- Chromatosome.
- Chromatid.
- Chromosome.
How much of the DNA of animals and plants is in the nucleus? Where in the cell is the rest found?
99% of the DNA of animals and plants is found in the nucleus. The rest is found in the mitochondria (of animals) and the chloroplasts (of plants).
Where is the DNA of bacteria found?
Free-floating in the cytoplasm.
How does the structure of RNA differ from DNA?
The sugar in RNA is ribose intead of deoxyribose - the hydrogen atom on C 2’ is replaced by an OH.
Thymine bases are replaced by uracil.
Is RNA more or less stable than DNA?
RNA is less stable than DNA. Because of the OH group on C 2’ of the sugar, it is susceptible to hydrolysis.
This is why vaccines based on RNA are cold-sensitive.
RNA is ……………. -stranded. This means that it can …………. into a variety of different …………. .
Single, fold, shapes.
What are the three types of RNA?
Ribosomal RNA (rRNA), transfer RNA (tRNA) and messenger RNA (mRNA).
Which RNA is this?
Many hundreds of different types in each cell.
Only a few copies of each type.
Very few uncommon bases.
Heterogenous size population 6S to 25S.
mRNA.
Which RNA is this?
The smallest RNA.
Contains 10% uncommon bases.
Many dfferent types in each cell.
Multiple copies of each different type within the cell.
Commonly has a clover leaf structure.
tRNA.
Which RNA is this?
Few types.
Occurs in very high numbers.
Very few uncommon bases.
Sizes in bacteria: 5S, 13S and 23S.
Sizes in mammalian cytoplasm: 5S, 7S, 18S and 28S.
Sizes in mammalian mitochondria: 16S, 18S.
Sizes in plant cytoplasm: 5S, 8S, 24S-28S.
Sizes in plant chloroplasts: 5S, 16S, 23S.
rRNA.
What are Svedberg numbers (S)?
Svedberg numbers are used to describe the size of RNA - the higher the Svedberg number, the larger the molecule.
Svedbergs are calculated using sedimentation in a centrifuge.
