DNA, RNA and protein synthesis Flashcards
What are the components of nucleotides?
A pentose sugar , either ribose or deoxyribose, a nitrogenous base, and a negatively charged phosphate group
Is ribose found in RNA or in DNA?
In RNA
Is deoxyribose found in DNA and RNA?
In DNA
What are the bases found in DNA?
Adenine, thymine, guanine, cytosine
What structure do purines have?
A double ring structure
Give some examples of purines
Adenine and guanine
What is the structure of a pyrimidine?
A single ring structure
What are some examples of pyrimidines?
Thymine and cytosine and uracil
What are the bases found in RNA?
Adenine, uracil, guanine and cytosine
What base replaces rhymine in RNA?
Uracil
What bond forms between the phosphate group of one nucleotide and the hydroxyl group on the carbon 3 of the other nucleotide?
A phosphodiester bond
What bond forms between the phosphate group of one nucleotide and the hydroxyl group on the carbon 3 of the other nucleotide? i.e 2 nucleotides
A phosphodiester bond
What is released when a phosphodiester bond forms?
Water and so this is a condensation reaction
what elements do nucleotides contain?
carbon, hydrogen, oxygen, nitrogen, and phosphorous
Draw a nucleotide
answer in book
How can a phosphodiester bond be broken?
By adding water in a hydrolysis reaction
Is DNA a polynucleotide?
yes
Is RNA a polynucleotide?
yes
how many polynucleotide strands does DNA consist of?
2
What’s on the outside of the polynucleotide strands in DNA?
A sugar-phosphate backbone
what’s on the inside of DNA’s polynucleotide chains?
bases , which are joined together by hydrogen bonds
the bases on one strand are ……. to the bases on another strand?
complementary
what does guanine pair with?
cytosine
what does adenine pair with?
thymine
what do purines pair with?
pyrimidines
are the 2 polynucleotide strands in DNA parallel or anti-parallel?
anti-parallel, which means they run in opposite directions
do different base pairs form the same number of hydrogen bonds?
no they form different numbers of hydrogen bonds
how many hydrogen bonds do guanine and cytosine form?
3
how many hydrogen bonds do adenine and thymine form?
2
why are the proportions of guanine and cytosine always the same as one another?
because of complementary base pairing
why are the proportions of adenine and thymine always the same as one another?
because of complementary base pairing
20% of the nucleotides in a sample of DNA contained the base guanine. Calculate the proportions of the other nucleotides?
20% cytosine, 30% adenine, 30% thymine
what is the shape of a DNA molecule called?
a double helix
what does RNA contain instead of thymine?
uracil
does RNA contain thymine?
no
where is DNA found?
in chromosomes in the nucleus
where is RNA found?
in the cytoplasm
Which molecule is longer, DNA or RNA?
DNA
How many polynucleotide strands does DNA contain?
1
What happens to the DNA in a cell every time a cell undergoes cell division?
all of its DNA is copied via a process called DNA replication
What are the steps or DNA replication?
- the enzyme DNA helicase attaches to the DNA molecule. DNA helicase causes the hydrogen bonds between complementary bases to break. This causes the 2 polynucleotide strands to separate from each other
-free nucleotides line up with their complementary bases on the DNA strands. At this stage, the free nucleotides are only held in place by hydrogen bonds between complementary bases, not phosphodiester bonds. The nucleotides are called activated nucleotides, as they have 3 phosphate groups
-the second enzyme, DNA polymerase, moves up and down the polynucleotides and catalyses the formation of phosphodiester bonds between the activated nucleotides. This is a condensation reaction. When the phosphodiester bonds form, the activated nucleotides lose their extra 2 phosphate groups and this provides the energy for the reaction.
what is the second step of DNA replication?
free nucleotides line up with their complementary bases on the DNA strands. At this stage, the free nucleotides are only held in place by hydrogen bonds between complementary bases, not phosphodiester bonds. The nucleotides are called activated nucleotides, as they have 3 phosphate groups
what is the third step of DNA replication?
the second enzyme, DNA polymerase, moves up and down the polynucleotides and catalyses the formation of phosphodiester bonds between the activated nucleotides. This is a condensation reaction. When the phosphodiester bonds form, the activated nucleotides lose their extra 2 phosphate groups and this provides the energy for the reaction.
Why is DNA replication an example of semi-conservative replication?
because each DNA molecule contains one strand from the original DNA molecule and one strand which is brand new
how many DNA molecules are produced in DNA replication?
2
What is it called when a DNA sequence is changed from the insertion of an incorrect base?
a mutation
mutations occur r……… and s………
randomly , spontaneously
who discovered the process of semi-conservative replication in DNA?
Meselson and Stahl
what is conservative replication?
where a DNA double helix is formed containing 2 new strands. The DNA molecule contains more of the original DNA
Do the bases in DNA all contain nitrogen?
yes
what are the 2 main isotopes of nitrogen atoms?
Nitrogen-14 and Nitrogen-15
What is the most common isotope of nitrogen?
Nitrogen-14, with over 99% of nitrogen atoms being nitrogen 14
which isotope of nitrogen is heavier, nitrogen-14 or nitrogen-15?
nitrogen-15
What does the position of the DNA band determine?
How heavy the DNA is
Is the DNA in prokaryotes circular or linear?
Circular with no free ends
Is the DNA in eukaryotes circular or linear?
Linear with 2 free ends
Is the DNA in prokaryotes bound to histone proteins?
No (doesn’t exist as chromosomes)
Is the DNA in eukaryotes bound to histone proteins?
Yes (forms chromosomes)
Are DNA molecules in prokaryotes long or short?
Relatively short
Are DNA molecules in eukaryotes long or short?
Long
How many copies of the DNA molecule are present after DNA replication?
2
Is it true that in semi conservative replication, each of the DNA molecules contains one strand from the original DNA molecule and one strand which is brand new?
Yes
What happens during a mutation?
An incorrect base is inserted into the growing polynucleotide strand. This changes the DNA sequence
Are mutations in the DNA sequence random?
Yes
Do mutations in the DNA sequence occur spontaneously?
Yes
What happens to the chromosomes in a cell before a cell divides?
All the chromosomes are copied. These 2 copies remain attached at a point called the centromere. The chromosomes then condense and the DNA and histones form densely packed loops and coilsand the chromosomes become visible in the cell
Is it true that a lot of DNA found in chromosomes doesn’t code for polypeptides?
Yes
What are the 2 main steps of protein synthesis?
Transcription and translation
In which part of the cell does DNA transcription take place?
In the nucleus
Describe all the steps of DNA transcription
1) DNA helicase breaks the hydrogen bonds between the 2 polynucleotide strands of DNA.
2) Complementary nucleotides move into place and form hydrogen bonds with the bases on the exposed nucleotides of one of the DNA strands.
3)RNA polymerase then joins the RNA nucleotides by forming phosphodiester bonds.
4) A strand of mRNA is now produced
5) Now that the mRNA has been synthesised, the RNA polymerase detaches from the DNA and the DNA goes back to its normal double helix structure.
6) The mRNA now moves out of the nucleus through a nuclear pore.
7) Once in the cytoplasm, the mRNA can now undertake translation
What is a gene?
A sequence of nucleotides that forms part of the DNA molecule
What are all of the genes in a cell called?
A genome
What determines the amino acid sequence of a protein?
The nucleotide sequence of a gene
What is the proteone?
All of the proteins produced by the Genome
mRNA nucleotides are read as a series of triplets. These triplets are called the genetic code. Is this true?
Yes
Do most amino acid have more than one triplet that codes for their amino acid?
Yes
How many triplets does gleucine have?
6
Because of the fact that most amino acids have more than one triplet that codes for them, what do scientists call the genetic code?
The “degenerate code”
What is meant by the fact that the genetic code is non-overlapping?
No base is read more than once
What is meant by the fact the genetic code is universal?
The same triplets encode the same amino acid in the vast majority of living organisms.
What does the start triplet tell you?
Where to start translating the mRNA molecule
What is the the start triplet?
AUG
What amino acid does AUG code for?
Methionine
What do the stop triplets do?
They determine where translation stops
What are the three stop triplets?
UAA, UAG, UGA
Is the nucleotide sequence of the mRNA used to determine the amino acid sequence of a protein?
Yes
What is each triplet in the mRNA called?
A codon
Describe that stages of protein translation
1) The small subunit of a ribosomes
Describe that stages of protein translation
1) The small subunit of a ribosome binds with the mRNA at the start codon.
2) a tRNA molecule with an anticodon complementary to the start codon attaches. This is held in place by hydrogen bonds between the complementary base pairs on the mRNA and tRNA
3)Now, a second tRNA molecule moves into place. The anticodon on this tRNA is complementary to the second codon on the mRNA.
4)Now, a peptide bond forms between the 2 amino acids produced. This forming of the peptide bond is catalysed by the enzyme peptidyl transferase. The formation of the peptide bond requires energy provided by ATP
5)Now, the ribosome moves to the next codon and forms a peptide bond with the next amino acid. The first tRNA molecule is now released (TRNA molecules that have been released are later attached to their amino acids by enzymes in the cytoplasm)
6) The ribosome continues moving down the mRNA, forming the polypeptide
7)When the ribosome comes to a stop codon, it detaches and the protein is released.
Can another ribosome attach to the start codon and start translating once the first ribosome has started moving along the mRNA molecule?
Yes
What can happen after the protein has finished being translated and has been correctly folded?
It can then carry out it’s function in the cell
What does ATP stand for?
Adenosine triphosphate
The energy released in the aerobic respiration of one glucose molecule can be transferre to how many molecules of ATP?
Over 30
Why is ATP a nucleotide?
Because it contains 3 phosphate groups, a pribose sugar and the base adenine
Does it take a lot of energy to break the covalent bond holding the last phosphate group in ATP in place?
No, it only takes a small amount of energy
What happens when the covalent bond holding the last phosphate group in ATP in place is broken?
A lot of energy is released. This energy can consequently be used by processes in the cell e.g the formation of large molecules, such as proteins
Why does the breaking of the covalent bond in atP a hydrolysis reaction?
Because a water molecule is required
ATP + water -≥ ADP + Pi +energy
What enzyme catalyses this reaction?
ATPase (ATP hydrolase)
What is another name for ATPase?
ATP hydolase
What does Pi stand for?
The inorganic phosphate group
Is ATP a long term energy store like glycogen or triglycerides?
No, it’s more of an immediate energy source, transferring energy from the sites of respiration ro the part of the cells which require energy
What are some examples of processes that requite ATP?
Active transport, muscle contraction, the formation of large molecules I.e proteins
What happens to the ADP and phosphate that are released in the hydrolysis of ATP?
They’re recycled back to ATP. This takes place during respiration in animal cells and in respiration and photosynthesis in plant cells
What is the reaction that iinvolves adding a phosphate back onto ADP called okay?
A phosphorylation reaction
What catalyses the adding of a phosphate back onto ADP?
ATP syntheses, water is released in this reaction, condensation
What are nucleic acids
Polymers that are made up of many nucleotides
Why is RNA not usually used as a storage molecule?
Because the presence of the carbon 2 hydroxyl group makes RNA more susceptible to hydrolysis
What are anabolic reactions ?
Reactions that build larger molecules from smaller molecules
Is ATP a phosphorylated nucleotide?
Yes
Read about DNA purification
Does semi Conservative replication ensure genetic continuity between generations of cells so that new cells inherit all their gened form their parents?
Yes
Does semi Conservative replication occur I prep for mitosis?
How many different codons (triplets) are possible?
How many different codons (triplets) are possible?
64 (there’s 4 bases)
Does semi Conservative replication occur in preparation for mitosis?
Yes
Does the degenerate nature of the genetic code limit the amount of mutations possible?
Yes
What are the advantages of Complementary Base Pairing?
-Allows for identical copies of DNA to be produced.
- Prevents mutations.
-Allows DNA to be replicated without error.
