2.3* Flashcards
What is a double helix?
Shape of a DNA molecule, due to coiling to two sugar-phosphate backbone strands into a right handed spiral configuration.
What is a monomer?
A molecule that when repeated makes up a polymer. Amino acids are the monomers of proteins. Nucleotides are the monomers of nucleic acids.
What is a nucleotide?
Molecule consisting of a five-carbon sugar, a phosphate group and a nitrogenous base.
What is a large molecule containing many nucleotides?
A polynucleotide.
What is a nucleotide?
Nucleotides are biological molecules that participate in nearly all biochemical processes. They are phosphate esters of pentose sugars, where a nitrogenous base linked to the carbon atom 1 of the sugar residue, and a phosphate group is linked to either carbon atom 5 or carbon atom 3 of the sugar residue, by covalent bonds formed by condensation reactions.
What do nucleotides form?
Nucleotides form the monomers of nucleic acids, DNA and RNA. In RNA the nucleotide pentose sugar is ribose. In DNA the nucleotide pentose sugar is deoxyribose.
When do nucleotides become phosphorylated nucleotides?
When they contain more than one phosphate group.
Give some examples of phosphorylated nucleotides.
ADP adenosine diposphate
ATP adenosine triphosphate
ATP is an energy-rich end-point of most energy-releasing biochemical pathways, and it is used to drive most energy-requiring metabolic processes in cells.
What do nucleotides help regulate?
Many metabolic pathways, for example by ADP and AMP (adenosine mono-phosphate)
What may nucleotides be components of?
Coenzymes
Give some examples of nucleotides that act as co-enzymes.
Adenine nucleotides are components of the co-enzymes NADP - nicotinamide adenine dinucleotide phosphate, which is used in photosynthesis, and of NAD (nicotinamide adenine dinucleotide), which is a co-enzyme used in respiration, and of FAD (flavine adenine dinucleotide) and co-enzyme A (both also involved in respiration).
Where is DNA found?
DNA is found in the nuclei of all eukaryote cell, within the cytoplasm of prokaryotic cells and is also inside some types of viruses.
What does DNA carry?
DNA is the hereditary material and carries coded instructions used in the development and functioning of all known living organisms.
What is DNA one of the most important?
DNA is one of the most important macromolecules that make up the structure of living organisms, the others being proteins, carbohydrates and lipids.
What is the structure of the polymer of DNA
DNA is a polymer as its made up of many repeating monomeric units called nucleotides.
A molecule of DNA consists of two stands made up of?
Polynucleotide
What does each DNA nucleotide consist of?
Each DNA nucleotide consists of a phosphate group, a five-carbon sugar called deoxyribose, and one of four nitrogenous bases; adenine, guanine, thymine or cytosine.
What type of bond exists between the sugar residue and the phosphate group in DNA?
A covalent bond.
What is the covalent bond between the sugar residue and the phosphate group in a nucleotide called? - DNA
A phosphodiester.
look at pg 87 for a diagram on condensation bonds.
How do nucleotides in DNA differ?
DNA consists of just four types of nucleotide. In each nucleotide the phosphate and sugar groups are the same but the organic (nitrogen) base differs.
What are the full names for the bases in DNA?
Adenine always pairs with thymine and Guanine always pairs with cytosine.
How are the two anti-parallel DNA strands joined to each other?
Hydrogen bonds between the nitrogenous bases.
Why do matching base pairs have to pair?
A purine always pairs with a pyrimidine to give equal sized rungs on the ladder.
Why do the DNA ‘rungs’ twist around an imaginary axis into a double helix?
To give the molecule stability.
What bases are purines?
Adenine and guanine
What bases are pyrimidines?
Thymine and cytosine
What bonds allows the nucleotides to unzip for transcription and replication?
hydrogen bonds.
Nucleotides with adenine as the base can make how many bonds with nucleotides with thymine as the base?
Two
Nucleotides with guanine as the base can make how many bonds with nucleotides with cytosine as the base?
Three
What is the upright part of the large DNA molecule that resembles a ladder formed by?
A sugar-phosphate backbone of the anti-parallel polynucleotide strand.
What does ‘opposite directions’ of two strands refer to?
It refers to the direction that the the 3rd and 5th carbon molecule on the 5-carbon sugar, deoxyribose, are facing.
Diagram on pg 88.
What is the 5’ end of the molecule?
Where the phosphate group is attached to the fifth carbon atom of the deoxyribose sugar.
Diagram on pg 88.
What is the 3’ end of the molecule?
Where the phosphate group is attached to the third carbon atom of the deoxyribose sugar.
Diagram on pg 88.
What do the rungs of the ladder consist of?
Complimentary base pairs, joined by hydrogen bonds.
Is the information within the base sequence protected?
The molecule is very stable, and the integrity of the coded information within the base sequences is protected.
How should you refer to bases within nucleic acids?
You should always refer to the bases within nucleic acids as nucleotide bases or nitrogenous/nitrogen containing bases, or as organic bases, because bases on its own refers to another group of chemicals.
What did and didn’t scientists know in the late 1800 about the nucleic acid DNA.
They knew that all nuclei of cells contained the nuclei acid DNA, but they did not know what it did. In fact it was referred to as ‘the stupid molecule’ as it was ubiquitous, but seemed to have no function.
At what time did which scientists help to work out the structure of DNA?
In 1953 the scientists James Watson, Frances Crick, Maurice Williams and Rosalind Franklin all helped to work out the structure of the DNA molecule.
When did which scientists receive the Nobel prize and why?
In 1963, Wilkins, Crick and Watson shared the Nobel prize for what was probably the most important biological discovery of the 20th century, and which spawned the beginning of modern molecular biology.
Who did not receive the Nobel prize?
Unfortunately, the x-ray crystallographer Franklin had already died of cancer, and the Nobel prize could not be awarded to her posthumously.
Explain the investigation that extracts and purifies DNA by precipitation.
All living organisms contain DNA, you can extract it from many sources for example strawberries and kiwifruit. The extracting process is very simple and involves simply macerating the tissue, adding a strong detergent (such as washing up liquid) and then adding ethanol so DNA precipitates out of solution. This DNA can be further purified by removal of unwanted salts and then can be concentrated.
How is DNA organised in a chromosome?
Each large molecule of DNA is round around special histone proteins into chromosomes. Each chromosome is therefore one molecule of DNA.
How is DNA organised in prokaryotic cells?
DNA is in a loop and is within the cytoplasm, not enclosed in a nucleus.
It is not wound around histone proteins, and is described as naked.
Where in the cell is there DNA that is not organised in chloroplasts?
There is also a loop of DNA, without the histone proteins, inside the mitochondria and chloroplasts.
What cells also have DNA in a loop?
Viruses that contain DNA also have it in the form of a loop of naked DNA.
What is DNA polymerase?
Enzyme that catalyses formation of DNA from activated deoxyribose nucleotides, using single stranded DNA as a template.
What is helicase?
Enzyme that catalyses the breaking of hydrogen bonds between nitrogenous pairs of bases in a DNA molecule
What is semi-conservative replication?
How DNA replicates, resulting in two new molecules, each of which contains one old strand and one new strand. One old strand is conserved in each new molecule.
Every time a cell divides why does the DNA need to be copied?
So each daughter cell receives a full set of instructions. Each molecule of DNA replicates.
When does cell replication take place?
This replication takes place during inter phase before the cell actually divides
What is a eukaryote?
A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes.
What does cell division result in for eukaryotes.
This results in each chromosome having an identical copy of itself. At first they are joined together at the centro-mere, forming two sister chromatids.
To make a new copy of itself what is the first two steps each DNA molecule must follow?
DNA must;
unwind - the double helix is untwisted, a bit at a time, catalysed by a gyrase enzyme.
Unzips - hydrogen bonds between the nucleotide bases are broken. This is catalysed by DNA helicase, and results in two single strands of DNA with exposed nucleotide bases.
In semi-conservative replication what happens to free phosphorylated nucleotides?
Free phosphorylated nucleotides, present in the nucleoplasm within the nucleus, are bonded to the exposed bases, following complementary base pairing rules.
In semi-conservative replication what does the enzyme DNA polymerase do?
The enzyme DNA polymerase catalyses the addition of new nucleotide bases, in the 5’ to 3’ direction, to the single strands of DNA; it uses each single strand of unzipped DNA as a template.
In semi-conservative replication How is the leading strand synthesised?
The leading strand is synthesised continuously, whereas the lagging strand is in fragments (discontinuous) that are later joined, catalysed by ligase enzymes.
In semi-conservative replication what is the purpose of the hydrolysis of the activated nucleotides?
To release extra phosphate groups, supplies the energy to make phosphodiester bonds between the sugar residue of one nucleotide and the phosphate group of the next nucleotide.
What is the product of semi-conservative replication?
Two DNA molecules, identical to each other and to the parent molecule. Each of these molecules contains one old strand and one new strand, and so this is termed semi-conservative replication.
What is a prokaryote?
A prokaryote is a single-celled organism that lacks a membrane-bound nucleus (karyon), mitochondria, or any other membrane-bound organelle.