DNA Flashcards
What is A Genome?
the totality of genetic information that is encoded in the DNA or RNA for some viruses.
why do we have different characteristics?
Each one of us has his own genetic information (DNA)
All living things are grouped into three domains:
Eukaryotes,Prokaryotes and Archea
what does (eu)(karyotes) mean?
eu means true, and karyotes stands for nucleus so true nucleus (in eukaryotes Dna is contained in a nucleus)
what does (Pro)(Karyotes) mean?
Pro means before, and karyotes stands for nucleus so before nucleus (in prokaryotes Dna is not contained in a nucleus)
what is generally more advanced, a Eukaryotic cell or a Prokaryotic cell?
Eukaryotic cell
what separates the nucleus from the rest of the cell (cytoplasm)?
a membrane called nuclear envelope
define chromosomes
structures that are considered carriers of genetic material
the genetic material is distributed along one chromosome or multiple chromosomes?
multiple chromosomes, with the number of chromosomes varying from species to another.
is eukaryotic DNA linear ?
Yes
what is the name of the proteins that are complexed within eukaryotic DNA?
histones
what does DNA stand for
Deoxyribonucleic acid
what is the term used to describe the structure of DNA
Double-helix
what is the main role of DNA
the long term storage of genetic instructions used in the development and functioning of all known living organisms and some
viruses
what is the double helix derived from
two polynucleotide chains that coil around each other
what is DNA often compared to?
DNA is often compared to a set of blueprints or a recipe, or a code, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules.
how many chromosomes do humans have in each cell
46
what are genes
DNA segments that carry genetic information.
what is a nucleotide
A nucleotide is the basic building block of nucleic acids (RNA and DNA)
what are the 3 things that make up a nucleotide
pentose sugar (Ribose in RNA and Deoxyribose in DNA), nitrogenous base and phosphate group.
what is a nucleoside
a nucleotide that has had all its phosphate groups removed
what are the 4 bases in DNA
adenine, guanine, cytosine, thymine
what are the 4 bases in RNA
adenine,guanine,cytosine, Uracil
how does uracil differ from thymine
it is lacking a methyl group on its ring
what type of bases are adenine and guanine
purines (fused five and six membered heterocyclic compounds)
what type of bases are cytosine and thymine
pyrimidines( six membered rings)
In living organisms, does DNA typically exist as a single molecule or as a pair of tightly held molecules?
DNA does not usually exist as a single
molecule, but instead as a pair of molecules that are held tightly
together.
What shape do the two long strands of DNA form when held together?
double helix
In a double helix, how is the direction of the nucleotides in one strand oriented compared to the other strand?
In a double helix the direction of the nucleotides in one strand
is opposite to their direction in the other strand: the strands are
antiparallels with asymmetric ends.
What is the term used to describe the opposing orientation of DNA strands in a double helix?
the strands are said to be antiparallel
What are the asymmetric ends of DNA strands called?
they are called the 5’ and 3’ ends
What group is found at the 5’ end of a DNA strand, and what group is found at the 3’ end?
the 5’ end having a terminal phosphate group and
the 3’ end a terminal hydroxyl group.
What is the term for the specific bonding between one type of base on one DNA strand and its corresponding base on the other strand?
complimentary base pairing
Which type of base forms hydrogen bonds with pyrimidines in complementary base pairing?
purines
In complementary base pairing, which base does adenine (A) bond with, and which base does cytosine (C) bond with?
with A bonding only
to T, and C bonding only to G.
What is the arrangement of two nucleotides binding together across the double helix called?
base pair
Why can hydrogen bonds between base pairs be broken and rejoined relatively easily?
they are not covalent bonds
Why are DNA’s two strands considered complementary to each other?
because the nucleotide sequence
of one strand determines the sequence of another strand
How does the nucleotide sequence of one DNA strand determine the sequence of the other strand?
due to complimentary base pairing
If one DNA strand has the sequence 5’-ACT-3’, what is the sequence of the complementary strand?
3’ -TGA- 5’
What base pairing rule do DNA strands follow, specifically with A
and C
pairings?
Note that they obey the (A:T) and (C:G) pairing rule.
Why does a DNA database only need to store the sequence of one strand?
because If we
know the sequence of one strand, we can deduce the sequence
of another strand.
By convention, which strand’s sequence is referred to in a DNA database, and in which direction is it written?
5’ to 3’ strand (left to right).
When is a DNA sequence referred to as the “sense” strand?
A DNA sequence is called “sense” if its sequence is the
same as that of a messenger RNA copy that is translated
into protein
What is the sequence on the opposite strand of the “sense” strand called?
The sequence on the opposite strand is called
the “antisense” sequence.
what is transcription
it is the process in which DNA is copied or is converted to mRNA
what is translation
the process by which a cell makes proteins using the genetic information carried in messenger RNA (mRNA)
What is the process called when DNA is twisted like a rope?
This process is called DNA supercoiling.
In its “relaxed” state, how often does a DNA strand circle the axis of the double helix?
In its relaxed state, a DNA strand circles the axis once every 10.4 base pairs.
What is positive supercoiling, and how does it affect the DNA?
Positive supercoiling occurs when the DNA is twisted in the same direction as the helix (counterclockwise), causing the bases to be held more tightly together.
What is negative supercoiling, and how does it affect the DNA?
Negative supercoiling happens when the DNA is twisted in the opposite direction of the helix, which makes the bases come apart more easily.
What type of supercoiling is most common in nature, and which enzymes introduce it?
Most DNA in nature has slight negative supercoiling, which is introduced by enzymes called topoisomerases.
What is the biological function of negative supercoiling in DNA?
Negative supercoiling helps facilitate the separation of DNA strands, which is important during processes like transcription and replication.
Why is negative supercoiling advantageous for DNA replication?
Negative supercoiling is advantageous because it makes DNA easier to unwind, which helps in replication. Positive supercoiling, being more condensed, would make separation more difficult.
What role do topoisomerases play in DNA transcription and replication?
Topoisomerases help by unwinding the DNA helix, making it easier for the DNA to undergo transcription and replication.
What do all the functions of DNA depend on?
All the functions of DNA depend on interactions with proteins.
How can protein interactions with DNA occur?
Protein interactions with DNA can be non-specific, or the protein can bind specifically to a single DNA sequence.
What type of proteins can bind specifically to a single DNA sequence?
Certain proteins can bind specifically to a single DNA sequence.
What is an example of an enzyme that binds to DNA?
An example of an enzyme that binds to DNA is polymerase.
What do polymerases do when they bind to DNA?
Polymerases copy the DNA sequence during transcription and DNA replication.
What holds DNA within chromosomes?
DNA is held in complexes with structural proteins within chromosomes.
What do structural proteins do to DNA
Structural proteins organize DNA into a compact structure called chromatin.
How is DNA organized in eukaryotes?
In eukaryotes, DNA binds to small basic proteins called histones, forming chromatin.
How does DNA organization differ between eukaryotes and prokaryotes?
In eukaryotes, DNA binds to histones, while in prokaryotes, multiple types of proteins are involved in organizing DNA.
What is the structure formed by histones and DNA?
Histones form a disk-shaped complex with DNA called a nucleosome.
How do histones bind to DNA?
Histones bind to DNA through non-specific interactions, where the basic residues of histones form ionic bonds with the acidic sugar-phosphate backbone of DNA.
What type of interaction occurs between histones and DNA?
The interaction is non-specific and involves ionic bonds between the basic residues in histones and the acidic sugar-phosphate backbone of DNA. This allows histones to organize and compact the DNA.
What is the basic structural unit of DNA packaging in eukaryotes?
The basic structural unit of DNA packaging in eukaryotes is the nucleosome.
What is the structure of a nucleosome?
A nucleosome consists of a segment of DNA wound around eight histone proteins.
What is chromatin?
Chromatin is the complex combination of DNA and proteins that makes up chromosomes.a
Where is chromatin found?
Chromatin is found inside the nuclei of eukaryotic cells.
What are the major components of chromatin?
The major components of chromatin are DNA and histone proteins.
What is the function of chromatin?
The function of chromatin is to package DNA into a smaller volume so it can fit inside the cell.
What is chromatin during cell division?
Chromatin is the substance that becomes visible as chromosomes during cell division.
What is the basic unit of chromatin?
The basic unit of chromatin is the nucleosome, which is composed of 146 base pairs (bp) of DNA and eight histone proteins.
How does the structure of chromatin change?
The structure of chromatin changes dynamically, at least in part, depending on the need for transcription.
What happens to chromatin during the metaphase of cell division?
During metaphase, chromatin condenses into visible chromosomes.
What is the state of chromatin when the cell is not dividing?
When the cell is not dividing, chromatin is less condensed.
What is heterochromatin?
Heterochromatin is a tightly packed form of chromatin that is generally transcriptionally inactive, meaning it is not usually involved in gene expression.
What is euchromatin?
Euchromatin is a loosely packed form of chromatin that is transcriptionally active, allowing for gene expression.
How do heterochromatin and euchromatin differ in their structure?
Heterochromatin is more condensed, making it tightly packed, while euchromatin is less condensed and more open.
What are histones?
Histones are proteins closely associated with DNA molecules.
What is the function of histones?
Histones have two main functions: they play a role in the structure of chromatin and are important in the regulation of gene expression.
How many types of histones have been identified?
Five types of histones have been identified: H1 (or H5), H2A, H2B, H3, and H4.
What role do H1 and H5 histones play?
H1 and its homologous protein H5 are involved in the formation of higher-order chromatin structures.
What role do the other four types of histones play?
The other four types of histones (H2A, H2B, H3, and H4) associate with DNA to form nucleosomes.
How are histones organized into superclasses?
Histones are organized into two superclasses: core histones (H2A, H2B, H3, and H4) and linker histones (H1 and H5).
What types of amino acids are abundant in histones?
Histones contain a high proportion of basic amino acids, specifically arginine and lysine, which help facilitate binding to the negatively charged DNA molecule.
What is the role of linker histones?
Linker histones (H1 and H5) bind to the DNA that enters and exits the nucleosome and help shift the equilibrium of chromatin toward a more condensed, higher-order structure.
Which histones are considered core histones, and what is their function?
Core histones include H2A, H2B, H3, and H4. They associate with DNA to form nucleosomes, the basic units of chromatin.
How do linker histones affect chromatin structure?
Linker histones promote the formation of more condensed, higher-order chromatin structures, which play a role in chromatin organization and gene regulation.
How is a nucleosome core particle formed?
Two of each core histone (H2A, H2B, H3, and H4) assemble to form a nucleosome core particle by wrapping 146 base pairs of DNA around the histone proteins in a 1.65 left-handed super-helical turn.
What is the role of the linker histone H1?
The linker histone H1 binds the nucleosome and the entry and exit sites of the DNA, locking the DNA in place and allowing the formation of higher-order chromatin structures.
how many base pairs of DNA are wrapped around the nucleosome core particle?
146 base pairs of DNA are wrapped around the nucleosome core particle.
What structural change does the linker histone H1 facilitate?
The linker histone H1 facilitates the formation of higher-order chromatin structures by locking the DNA into place around the nucleosome.
What is a chromosome?
A chromosome is an organized structure of DNA and protein found in cells.
What does a chromosome contain?
A chromosome contains a single piece of coiled DNA that includes many genes, regulatory elements, and other nucleotide sequences.
What role do DNA-bound proteins play in chromosomes?
DNA-bound proteins in chromosomes serve to package the DNA and control its functions.
What type of chromosome do prokaryotes typically have?
Prokaryotes, including bacteria and archaea, typically have a single circular chromosome.
Are there variations in prokaryotic chromosomes?
Yes, there are many variations of prokaryotic chromosomes.
How does the size of prokaryotic chromosomes vary?
The size of prokaryotic chromosomes differs from species to species, measured in base pairs.
