LAST SET OF LECTURES (13-17) Flashcards
what are the two types of nucleic acid
RNA and DNA
what are the funtions of nucleic acid
-storage of info
-transfer of info
- expression of genetic info
-CO-ENZYMES: essential parts of many enzymes, and
necessary for their function
-SIGNALING MOLECULES: cAMP
-TRANSFER OF CHEMICAL ENERGY in all cells: i.e. ATP, GTP and ADP.
how do nucleic acids hold “the instructions” for the creation of one living organsism
protein
synthesis.
How is DNA replicated for cell division
mitosis or
meiosis
What makes up a nucletoide (monomer of nucleic acid)
nitrogenous base, sugar pentose, and one or more phosphate group(s)
what are the nitrogenous bases that make up nucleotides
Pyrimidines
1-ring molecule
Cytosine (has an amino gorup) (both), Thymine (methyl group)
(T in DNA)/Uracil (dbl bonded O) (U in RNA)
Purines
2-ring molecule
Adenine ( amino group and HC) (both) and
Guanine (NH and NH2) (both)
CG AND AT
what are the sugar backbones in nucleic acids. WHat makes them different?
Deoxyribose and Ribose
The only difference between the sugar in DNA and RNA is that DNA lacks an oxygen
atom on the second carbon of its ring.
how do yu differentiate the carbons of the sugar carbons from the attached nitrogenous base?
- the carbons on the sugar ring have a prime (’) after them.
- Therefore, the different carbon is the 2’ carbon and the carbon that sticks up
is the 5’ carbon.
what makes the structural backbone of the nucleic acid
the sugar and phosphate groups of a nucleotide
what is a phosphosiester bond
, the phosphate
group of 1 nucleotide
covalently bonds with the sugar
of another nucleotide. This is a dehydration synthesis rx
T or F each end of a polynucleotude strand is different
True
One side ends with a phosphate group
attached to the 5’ carbon.
The other side ends with a hydroxyl group
attached to the 3’ carbon.
* These are thereby referred to as the 5’ end and
3’ end respectively.
nucleic acid codes are always read in the ___ to ___ direction
5’, 3’ (OH)
what is the main diff between RNA and DNA
RNA
single stranded.It has one strand of
polynucleotides that
twists around itself.
DNA
double stranded. It has 2 strands of polynucleotides
linked together by hydrogen bonds
between their nitrogenous bases.
why is RNA useful ?
RNA is the product of transcription of specific DNA sequences called genes.
Some RNA strands are used
to carry out specific tasks
(e.g. tRNA, rRNA and
ribozymes).
Others are used to determine the
sequence of amino acids that
comprise the primary structure of
a protein (mRNA).
recall two types of RNA
mRNA
A complimentary
RNA strand to a gene (in red)
used to make a protein
tRNA
Facilitate the process of
translation during protein
synthesis
define ribozymes. How can RNA be ribozymes
Ribozyme: Ribonucleic acid enzyme
rRNA in the large subunit of the ribosome
catalyzes peptide bond formation during
translation.
RNA can associate with itself in
complementary base-pairing and fold into
more complex conformations.
- This specific folding is what allows RNA to
serve specific functions in cells such as
ribozymes.
define spliceosomes
Certain ribozymes called spliceosomes
catalyze reactions during RNA splicing
what is particular about the double stranded DNA order?
- Each of DNA’s two
strands have a 5’
and a 3’ end. - The directions of
each strand are
inversed relative to
the other. - The backbones run
in opposite 5’ → 3’
directions.
THE TWI POLYNUCLETOIDES ARE ANTIPARALLEL
how many hydrogen bonds are formed between nitrogebous bases
C and G form 3 H bonds
Thymine and Adenine form 2 H bonds
What was determined by A.Hershey and M. Chase
- when bacteriophages (composed of DNA
and protein), infect bacteria, their DNA
enters the host bacterial cell. - but most of their protein did NOT enter
the host bacterial cell. - served to prove that DNA is the hereditary
material.
What is Chargaff’s rule?
Since A and T always base-pair
together:
% of A is equal to the %
of T
Since G and C always base-pair
together:
% of G is equal to the %
of C
Chargaff’s rule remained unexplained until the discovery of the
double helix structure of DNA.
How did Watson, Crick and Franklin’s discovery of the double-stranded nature of DNA explain this rule
The uniform diameter of the double helix
suggested that purines must be paired with
pyrimidines.
-This finding explained Chargaff’s rule.
Watson and Crick hinted that since DNA bases can form pre-determined pairs, one
strand can be used as a template for creating another a built-in replication
mechanism.
DNA replication is semi-conservative.
Each newly formed daughter strand
is formed from part of the original
strand and is partly new (making it
not fully conservative to semiconservative).
Why do cells replicate DNA
➢ Growth and development
➢ Tissue Renewal (ex: skin cells, red blood cells)
➢ Germ Cell Production
DNA replication is semi conservative. What does this mean?
Semiconservative replication entails the replication of one parental strand to give its complementary strand and the replication of the other parental strand to give its complementary strand; each parental strand then stays with its newly replicated, complementary strand
How many chromosomes are in one somatic cell in humans
46
How do prokaryotes syntheisze new DNA (BRIEF UNDERSTANDING)
- At the origins of replication, short stretches of DNA that have a specific sequence of nucleotides
- proteins that intiiate DNA replication recognize the sequence and attach to the DNA, seperating the two strands and opening at replication “bubble”
- Parent DNA will be copied to both direction from the origin at the same time until the whole chromosome is replicated
- Each end of a replication bubble has a replication fork. Since replication happens in both direction from the origin, there are one at each end of the bubble
- enzymes and other proteins partake in replicating the DNA
define replication fork
, a Y-shaped
region where the parental strands
of DNA are being unwound.
what are the DETAILED steps of prokaryote DNA replication (replication factory)
- Unzipping the double stranded DNA
- Helicase (enzyme): unzips the complementary polynucleotide strands at the origin of replication
-SSBP (sing-stranded building protein)
Adhere to the seperated polynucleotide strands ti prevent reannealing (strands “zipping” back up) - Release the tension (Separation of the polynucleotide
strands leads to supercoiling in
the DNA molecule ahead of the
replication fork. )
- Topoisomerase (enzyme)
Helps relieve this strain by breaking swiverling and rejoining DNA strands. - Synthesizing the new strand
- Primase (enzyme)
synthesize a primer (short chain of RNA) and uses parental DNA as a template
- DNA ploymerase (enzyme)
Catalyzes the polymerization of DNA nucleotides - Synthesize the new complementary DNA strand
- DNA polymerase III (enzyme)
Adds complementary DNA nucleotides to the free 3’ end of the strand. Complementary DNA strands can only be elongated in the 5’ to 3’ direction
- Sliding clamp
Ensures DNA Pol III maintains contact witht he template strand during the polymerization process - The fifth step is to remove the RNA primers and replace them with DNA nucleotides
- Rnase H (enzyme)
Recognizes RNA-DNA hybrid segments and degrades the RNA primer by hydrolyzing its phosphodiester bonds
- DNA polymerase I (enzyme)
adds DNA nucletoides to any exposed 3’ ends on the leading and lagging strands - Gluing of the lagging strands together
- DNA ligase (enzyme)
attaches adjacent fragments of DNA on the newly synthesized strands to make a continuous polynucleotide strand
T or F DNA Polymerase can only add nucleotides to the 3’ end of an
existing polynucleotide strand
T
Because DNA pol III can only
add nucleotides to an open 3’
end, what is the
implications on the two
replication forks:
➢Leading strand
➢Lagging strand
(Each replication fork has a leading
strand and a lagging strand)
- Along one template strand, DNA Pol III can synthesize a complementary strand
continuously in the mandatory 5’ → 3’ direction. This new DNA strand is called
the leading strand. - To elongate the other new strand in the mandatory 5’ to 3’ direction, DNA pol III
must work along the other template strand in the direction away from the
replication fork. The new DNA strand synthesized in this way is called the lagging
strand.
What is pertitnent about a leading strand (STEP 4 replication factory)
- Only one RNA primer is
required for each leading
strand - it will be synthesized
continuously in same the
direction of the
replication fork’s
movement. - As the parent DNA
unwinds, the opening
space in front of the
leading strand allows
continuous adding of
nucleotides to an open 3’
end.
what is pertienent about a lagging strand? (STEP 4 replication factory)
- the lagging strand is
synthesized discontinuously,
as a series of segments. - Lagging strands grow in the
opposite direction from the
movement of the
replication fork. - They are produced in short
segments called Okazaki
Fragments as the parent
template strand is slowly
more and more exposed. - DNA Polymerases can only
add nucleotides to the 3’
end of a polynucleotide
strand which has and
exposed hydroxyl group. - So even though the
replication fork is moving
away from the origin, the
lagging strand can only grow
by Okazaki fragments in the
direction towards the origin
of replication
T or F not every okazaki fragment requires a new primer
F Each Okazaki fragment
requires a new primer.
What is the DNA replication complex
The various proteins that participate in DNA replication actually form a single
large complex, a “DNA replication machine.” Many protein-protein
interactions facilitate the efficiency of this complex.
how does the DNA replication complex move
The DNA replication complex
may not move along the DNA;
rather, the DNA may move
through the complex during
the replication process.
What is the difference between dna replication in eukaryotes and prokaryotes
- Eukaryotic DNA contains many more
base pairs: (6 billion in humans)
compared to prokaryotic DNA (~ 5
million). - Replication therefore takes longer than
for prokaryotes (a few hours in
humans). - Eukaryotic DNA is in multiple linear
strands unlike the circular DNA of
prokaryotes. - The ends of these linear strands are
vulnerable to damage and are
therefore protected by telomeres
(DNA extensions).
what are telomeres
- Telomeres are short repeated DNA
sequences (TTAGGG) at both ends of a
linear DNA strand which contain no
genes.
t or f, telomeres do not get shorter with each replication event
False, they do
* The end of the molecule on each
lagging strand is left un-replicated
and the exposed section on the
parent strand breaks off.
what are the two protective functions of telomeres
➢ Specific associated proteins prevent
the activation of DNA damage
signaling.
➢ Provides some protection against
the organism’s genes shortening.
true or false, telomeres acts as a buffer and completely prevent the erosion of near the ends of chromosome
false
* Telomeres acts as a buffer. However,
telomeres do not completely
prevent the erosion of genes near
the ends of chromosomes; they
merely postpone it.
what is telomerase
Telomerase is an enzyme which
can extend the length of
telomeres.
where is telomerase found
➢ Germ cells (undergo meiosis
to make gametes)
➢ Cells within
embryos/fetuses
➢ Certain tumor cells
fun fact: Stem cells in adults don’t have
telomerase, so the ends of their
DNA get shorter with time.
what is an advantage of normal shortening of telomerase
Normal shortening of telomeres may protect organisms from cancer by limiting the number
of divisions that somatic cells can undergo. Many cancer cells seem capable of unlimited cell
division, as do immortal strains of cultured cells.
