Nucleic Acids: Structure & DNA Replication (AQA A Level Biology): Flashcards
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What three components make up a nucleotide?
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What three components make up a nucleotide?
A nucleotide consists of a pentose sugar, a phosphate group, and a nitrogen-containing organic base.
Define phosphodiester bond.
A phosphodiester bond is a chemical bond formed between the phosphate group of one nucleotide and the pentose sugar of another, creating the sugar-phosphate backbone in nucleic acids.
DNA and RNA are made up of many repeating units called .
DNA and RNA are polymers made up of many repeating units called nucleotides.
Which sugar is present in a DNA nucleotide?
A deoxyribose sugar is present in a DNA nucleotide.
RNA nucleotides contain the sugar and the base , which is not found in DNA.
RNA nucleotides contain the sugar ribose and the base uracil, which is not found in DNA.
True or False?
Both DNA and RNA can contain the base thymine.
False.
Only DNA contains the base thymine, while RNA contains uracil instead.
Define sugar-phosphate backbone.
The sugar-phosphate backbone is the repeating chain of pentose sugars and phosphate groups joined by phosphodiester bonds in nucleic acids.
What makes RNA more susceptible to hydrolysis than DNA?
RNA is more susceptible to hydrolysis because it has a hydroxyl (OH) group at the 2' position of its ribose sugar.
A condensation reaction between two nucleotides forms a .
A condensation reaction between two nucleotides forms a phosphodiester bond.
What are the four nitrogenous bases found in DNA?
The four nitrogenous bases in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T).
In DNA, the sugar is , while in RNA, the sugar is .
In DNA, the sugar is deoxyribose, while in RNA, the sugar is ribose.
Define polynucleotide.
A polynucleotide is a long chain molecule made up of many nucleotides bonded together.
Which three components make up a single DNA nucleotide?
A DNA nucleotide consists of a phosphate group, a deoxyribose sugar, and a nitrogenous base.
DNA is composed of two strands that run in directions.
DNA is composed of two polynucleotide strands that run in antiparallel directions.
Define phosphodiester bond.
A phosphodiester bond is a covalent bond that links the phosphate group of one nucleotide to the deoxyribose sugar of the next nucleotide in the DNA backbone.
What is meant by complementary base pairing in DNA?
Complementary base pairing means that adenine always pairs with thymine and guanine always pairs with cytosine via hydrogen bonds in the DNA molecule.
The sugar-phosphate backbone of DNA is formed by alternating sugars and groups.
The sugar-phosphate backbone of DNA is formed by alternating deoxyribose sugars and phosphate groups.
Define double helix.
A double helix is the three-dimensional shape of DNA, where two polynucleotide strands twist around each other to form a spiral structure.
True or False?
Hydrogen bonds in DNA always form between the same pairs of nitrogenous bases.
True.
In DNA, adenine always pairs with thymine and guanine always pairs with cytosine through hydrogen bonds.
The function of DNA is to genetic information for the growth and development of an organism.
The function of DNA is to store genetic information for the growth and development of an organism.
What are the two ends of a DNA strand called, and how are they determined?
The two ends of a DNA strand are called the 3’ end and the 5’ end, determined by which carbon atom of the deoxyribose sugar is free for bonding.
Define hydrogen bond (in DNA).
A hydrogen bond in DNA is a weak bond that forms between complementary nitrogenous bases on opposite strands, helping to hold the two DNA strands together.
Define RNA (ribonucleic acid).
RNA (ribonucleic acid) is a single-stranded polynucleotide made of nucleotides containing the sugar ribose, and the bases adenine, guanine, cytosine, and uracil.
Which nitrogenous base is found in RNA but not in DNA?
The nitrogenous base uracil is found in RNA but not in DNA.
RNA nucleotides contain the sugar , while DNA nucleotides contain the sugar .
RNA nucleotides contain the sugar ribose, while DNA nucleotides contain the sugar deoxyribose.
What is a polynucleotide?
A polynucleotide is a long chain of many nucleotides linked together by covalent bonds.
What type of bond forms the sugar-phosphate backbone in RNA?
The sugar-phosphate backbone in RNA is formed by phosphodiester bonds.
Unlike DNA, RNA molecules are -stranded and are usually than DNA molecules.
Unlike DNA, RNA molecules are single-stranded and are usually shorter than DNA molecules.
True or False?
Messenger RNA (mRNA) is a double-stranded molecule that encodes a specific polypeptide.
False.
mRNA is a single-stranded molecule that encodes a specific polypeptide.
RNA's function is to the genetic code from the nucleus to the , where proteins are made.
RNA's function is to transfer the genetic code from the nucleus to the ribosomes, where proteins are made.
What is the role of ribosomal RNA (rRNA)?
Ribosomal RNA (rRNA) is a type of RNA that, together with proteins, forms ribosomes, the site of protein synthesis in cells.
Define ribosome.
A ribosome is a small organelle found in all cells, free in the cytoplasm or attached to the rough endoplasmic reticulum, where protein synthesis occurs.
What is the main function of ribosomes in a cell?
The main function of ribosomes is to synthesise proteins by reading RNA and assembling amino acids into polypeptides during translation.
Ribosomes are composed of a mixture of and .
Ribosomes are composed of a mixture of ribosomal RNA and proteins.
True or False?
The rRNA in ribosomes only provides structural support and has no enzymatic activity.
False.
The rRNA in ribosomes has enzymatic properties and catalyses the formation of peptide bonds between amino acids.
What is the difference between 80S and 70S ribosomes?
80S ribosomes (composed of 60S and 40S subunits) are found in eukaryotic cells, while 70S ribosomes (composed of 50S and 30S subunits) are found in prokaryotic cells, and in the mitochondria and chloroplasts of eukaryotic cells.
During translation, sits between the two subunits of the ribosome, which moves along it to assemble a .
During translation, mRNA sits between the two subunits of the ribosome, which moves along it to assemble a polypeptide.
True or False?
Ribosomes are surrounded by a phospholipid membrane like other organelles.
False.
Ribosomes are not surrounded by a membrane, unlike some other organelles.
Ribosomes are either free in the or attached to the endoplasmic reticulum.
Ribosomes are either free in the cytoplasm or attached to the rough endoplasmic reticulum.
What is the role of the large subunit of a ribosome during translation?
The large subunit is the site of translation.
Its rRNA and proteins hold tRNA molecules (with their attached amino acids) in place, so that peptide bonds can form between amino acids.
Define translation.
Translation is the process in which ribosomes 'read' RNA to assemble amino acids into polypeptides (proteins).
True or False?
Ribosomes in eukaryotic cells are larger than those in prokaryotic cells.
True.
Eukaryotic 80S ribosomes are larger than prokaryotic 70S ribosomes, though both are made of a small subunit and a large subunit.
Define DNA.
DNA is a deoxyribonucleic acid molecule that carries the genetic code for living organisms and is composed of repeating nucleotides.
Who was the first scientist to discover DNA and what did he originally call it?
Friedrich Miescher was the first scientist to discover DNA, originally naming it nuclein.
At first, many scientists doubted that could carry the genetic code because of its chemical composition.
At first, many scientists doubted that DNA could carry the genetic code because of its relatively simple chemical composition.
Define a nucleotide.
A nucleotide is the basic subunit of DNA, consisting of a phosphate group, deoxyribose sugar, and a nitrogen-containing organic base.
What was eventually accepted about the role of DNA, despite early doubts?
That DNA carries the genetic code and is the hereditary material, despite its relatively simple chemical composition.
True or False?
DNA is located in the cytoplasm, making it vulnerable to hydrolysis.
False.
DNA is located in the nucleus, which protects the genetic material. Proteins are found in the cytoplasm and are more susceptible to hydrolysis.
Who confirmed the double-helix structure of DNA using X-ray data in 1953?
The double-helix structure of DNA was confirmed by Watson and Crick in 1953, using Rosalind Franklin’s X-ray data.
Despite having only types of nucleotides, the use of the code allows for great variation in genetic information.
Despite having only four types of nucleotides, the use of the triplet code allows for great variation in genetic information.
Define semi-conservative replication.
Semi-conservative replication is a process in which each new DNA molecule consists of one original strand and one newly synthesised strand.
What is the purpose of copying DNA before a cell divides?
Copying DNA before cell division ensures that each daughter cell receives a full copy of the parental DNA, maintaining genetic continuity.
Each new DNA molecule produced by semi-conservative replication consists of and .
Each new DNA molecule produced by semi-conservative replication consists of one original strand and one newly synthesised strand.
What phase of the cell cycle does DNA replication occur in?
DNA replication occurs during the S phase of interphase in the cell cycle.
Define genetic continuity.
Genetic continuity is the maintenance of identical genetic information across generations of cells, ensured by accurate DNA replication.
Which enzyme unwinds the DNA double helix during replication?
The enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between base pairs.
The enzyme catalyses condensation reactions to form the during DNA replication.
The enzyme DNA polymerase catalyses condensation reactions to form the sugar-phosphate backbone during DNA replication.
True or False?
Free nucleotides must be activated to provide energy for DNA replication.
True.
Free nucleotides exist as nucleoside triphosphates, and the extra phosphate groups provide the energy needed for DNA replication.
Define complementary base pairs.
Complementary base pairs are pairs of nitrogenous bases in DNA that always bond together: adenine with thymine (A-T) and cytosine with guanine (C-G).
Which four nitrogenous bases are found in DNA?
The four nitrogenous bases in DNA are adenine (A), cytosine (C), thymine (T), and guanine (G).
In DNA, always pairs with thymine, and cytosine always pairs with .
In DNA, adenine always pairs with thymine, and cytosine always pairs with guanine.
True or False?
In a DNA molecule, the percentage of adenine always equals the percentage of thymine.
True.
Because adenine always pairs with thymine, they are present in equal amounts in double-stranded DNA.
All DNA nucleotides contain the same phosphate group and , but the attached can vary between nucleotides.
All DNA nucleotides contain the same phosphate group and deoxyribose sugar, but the attached nitrogenous base can vary between nucleotides.
If 30% of the bases in a DNA molecule are thymine, what percentage are cytosine?
If 30% are thymine, then 30% are adenine (A-T pairing), leaving 40% for cytosine and guanine together. Therefore, cytosine makes up 20% of the bases.
In a section of DNA, 28% of the bases are cytosine. What percentage are guanine?
28%.
Cytosine always pairs with guanine (C-G), so their frequencies are equal; therefore guanine also makes up 28% of the bases.
In a section of DNA, 28% of the bases are cytosine. What percentage are adenine?
22%.
Cytosine and guanine together make up 56% (C = G = 28%), leaving 44% for adenine and thymine.
As A = T, adenine makes up 22% of the bases.
The frequency of adenine is always equal to the frequency of , and the frequency of cytosine is always equal to the frequency of .
The frequency of adenine is always equal to the frequency of thymine, and the frequency of cytosine is always equal to the frequency of guanine.
Why is the frequency of adenine always equal to the frequency of thymine in double-stranded DNA?
Adenine and thymine are complementary bases that always pair together (A-T).
Each adenine on one strand is matched by a thymine on the other strand, so their frequencies are equal.
If 20% of the bases in a DNA molecule are guanine, then cytosine also makes up 20%, leaving 60% shared equally between adenine and thymine, so adenine makes up %.
If 20% of the bases in a DNA molecule are guanine, then cytosine also makes up 20%, leaving 60% shared equally between adenine and thymine, so adenine makes up 30 %.
In what year did Watson and Crick confirm the double-helix structure of DNA?
Watson and Crick confirmed the double-helix structure of DNA in 1953.
Define semi-conservative replication.
Semi-conservative replication is a model of DNA replication in which each new DNA molecule contains one original strand and one newly synthesised strand.
The conservative model suggested that the original DNA remains , and the new DNA is made entirely of .
The conservative model suggested that the original DNA remains intact, and the new DNA is made entirely of new strands.
Which base pairs with adenine in DNA?
In DNA, thymine pairs with adenine.
Define conservative DNA replication.
Conservative DNA replication is a theory that suggested the original DNA molecule would stay together, and the new DNA molecule would be made out of two brand-new strands.
Meselson and Stahl used bacteria grown in a broth containing the heavy isotope .
Meselson and Stahl used bacteria grown in a broth containing the heavy isotope ¹⁵N.
During Meselson and Stahl’s experiment, where did DNA containing only ¹⁵N settle after centrifugation?
DNA containing only ¹⁵N settled near the bottom of the centrifuge tube.
If semi-conservative replication occurred, the DNA would settle in the of the centrifuge tube after one round.
If semi-conservative replication occurred, the DNA would settle in the middle of the centrifuge tube after one round.
True or False?
Meselson and Stahl’s experiment proved that DNA replicates through a semi-conservative mechanism.
True.
Their experiment showed that each new DNA molecule contained one original and one new strand, supporting the semi-conservative model of DNA replication.
Define centrifugation.
Centrifugation is a technique that separates substances of different densities by spinning them at high speed, as used by Meselson and Stahl to distinguish DNA with different nitrogen isotopes.
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