2.3 Nucleotides And Nucleic Acids Flashcards
Examples of Nucleic acids
DNA AND RNA
Nucleic acids
polymers that are made up of many repeating units (monomers) called nucleotides
What is each nucleotide formed from
A pentose sugar (a sugar with 5 carbon atoms)
A nitrogen-containing organic base
A phosphate group
Components of DNA nucleotides
A deoxyribose sugar with hydrogen at the 2’ position
A phosphate group
One of four nitrogenous bases - adenine (A), cytosine(C), guanine(G) or thymine(T)
Components of RNA nucleotides
A ribose sugar with a hydroxyl (OH) group at the 2’ position
A phosphate group
One of four nitrogenous bases - adenine (A), cytosine(C), guanine(G) or uracil (U)
Why is RNA more susceptible to hydrolysis and what does this mean
The presence of the 2’ hydroxyl group
This is why DNA is the storage molecule and RNA is the transport molecule with a shorter molecular lifespan
Nitrogenous base of DNA
Adenine, cytosine, guanine or thymine (A,T,C,G)
Nitrogenous bases of RNA
Adenine, cytosine, guanine or uracil (A,U,C,G)
What two structural forms to nitrogenous bases found in nucleotides of DNA and RNA
Purines and pyrimidines
What structural form are adenine and guanine
Purine- they have a double ring structure
What structural form do cytosine, thymine and uracil have
Pyrimidines- they have a single ring structure
Pentose sugar of DNA
Deoxyribose
Pentose sugar of RNA
Ribose
Number of strands in DNA
Double stranded (double helix)
Number of strands in RNA
Single stranded
What makes DNA and RNA polymer
they are made up of many nucleotides joined together in long chains
How are separate nucleotides joined together
Condensation reactions
Where do the condensation reactions occur (nucleotides)
between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide
What does a condensation reaction between two nucleotides form
Phosphodiester bond
What does a Phosphodiester bond consist of
A phosphate group and two (di) ester bonds- phospho(di)ester
What is the chain of alternating phosphate groups and pentose sugars produced as a result of many phosphodiester bonds known as
the sugar-phosphate backbone (of the DNA or RNA molecule)
What does the synthesis of polynucleotides require
formation of phosphodiester bonds
What does the breakdown of polynucleotides require
the breakage of phosphodiester bonds
What happens in condensation reactions
A molecule of water is released
What happens in hydrolysis reactions
A molecule of water is added
What is energy required for in all organisms
Anabolic reactions
Moving substances across the cell membrane or moving substances within a cell
Anabolic reactions
Building larger molecules from smaller molecules
What is energy required for in animals
Muscle contraction – to coordinate movement at the whole-organism level
The conduction of nerve impulses
What is ATP used for in all known life forms
ATP from respiration is used to transfer energy in all energy-requiring processes in cells
What is Adenosine Triphsphate (ATP) and how does it link to DNA and RNA
A nucleotide
The monomers of DNA and RNA are also nucleotide
What is Adenosine triphosphate (ATP)
the energy-carrying molecule that provides the energy to drive many processes inside living cells
What type of nucleotide is ATP
a phosphorylated nucleotide
Phosphorylated
Phosphorylation involves the addition of phosphate to an organic compound
Why is ATP structurally similar to the nucleotides that make up DNA and RNA
ATP is another type of nucleic acid and hence it is structurally very similar to the nucleotides that make up DNA and RNA
What does Adenosine diphosphate (ADP) consist of
Sugar ribose, the base adenine and two phosphate groups
What does Adenosine triphosphate (ATP) consist of
Same ribose sugar and base adenine as ADP, but contains three phosphate groups
What is DNA and what is it made up of
a polynucleotide – it is made up of many nucleotides bonded together in a long chain
What are DNA molecules made up of
DNA molecules are made up of two polynucleotide strands lying side by side, running in opposite directions – the strands are said to be antiparallel
What is each DNA polynucleotide strand made up of
alternating deoxyribose sugars and phosphate groups bonded together to form the sugar-phosphate backbone
What type of bonding is involved in each DNA polynucleotide strand
These bonds are covalent bonds known as phosphodiester bonds
What are the strands known as
As the strands run in opposite directions (they are antiparallel), one is known as the 5’ to 3’ strand and the other is known as the 3’ to 5’ strand
What holds together the two anti parallel DNA polynucleotide strands
Hydrogen bonds
Where do the hydrogen bonds occur (DNA)
The same bases
What does the purine adenine bond with
The pyrimidines thymine- two hydrogen bonds formed between these bases (A and T)
What does the purine guanine pair with
The pyrimidines cytosine- three hydrogen bonds are formed between these bases (G and C)
What is the process of the hydrogen bonds between bases known as
Complementary base pairing with the pars known as complementary base pairs
Why is DNA referred to as a double helix
the three-dimensional shape formed by the twisting of the DNA molecule
What process is used to purify (isolate) DNA
Precipitation
A common method used to isolate DNA is Marmus preparation
What three basic steps are involved
Breaking (lysing) the cells and disrupting the nuclear membranes to release the DNA
Using enzymes to denature and remove the proteins (histones) associated with the DNA
Precipitating the DNA using an organic solvent (e.g. ethanol)
Why are onions good for extracting DNA investigation
Onions are good to use for this investigation as their cells contain a relatively large amount of DNA
Method for onion DNA practical 1
Place the ethanol in a freezer 24 hours before starting the investigation
The ethanol must be ice-cold, it is key to the success of the investigation
Method for onion DNA practical 2
Cut up the onion into small pieces (5 mm × 5 mm)
Add the washing-up liquid to 90 cm³ of tap water in a beaker
Add some of the onion pieces to the beaker
Method for onion DNA practical 3
Place the beaker in a water bath at 60 °C for 15 minutes
The detergent (washing-up liquid) and the heat disrupt the phospholipid bilayer of the onion cell membranes and nuclear membranes, releasing the DNA
The heat also denatures enzymes released from the cell that would otherwise begin to digest the DNA
Method for onion DNA practical 4
Cool the mixture in an ice-water bath for 5 minutes, stirring it continually
Lowering the temperature prevents the DNA itself from breaking down, which would occur if the high temperature from the previous step was maintained
Continual stirring ensures the whole mixture is cooled
Method for onion DNA practical 5
Pour the mixture into a blender and blend for 5 seconds
Blending breaks down the cell walls and cell membranes of the onion cells even further, releasing more DNA
The mixture is only blended for a very short time to ensure the DNA strands themselves are not broken apart
Method for onion practical 6
Using the filter paper, filter the mixture into another beaker
Filtering removes cell debris and membrane fragments
The filtrate now contains the DNA and its associated proteins
Method for onion practical 7
Pour 10 cm³ of the filtrate into a test tube and add 2-3 drops of protease enzyme, mixing well
The protease denatures and removes the proteins, leaving just the DNA
Method for onion practical 8
Carefully add the ice-cold ethanol to the test tube and wait 2-3 minutes
Nucleic acids are insoluble in ice-cold ethanol and so the DNA forms a precipitate (white layer) at the top of the test tube mixture
What does a parent cell have to do before it divides
It needs to copy the DNA contained within it
What does replicating DNA ensure
that the two new (daughter) cells produced will both receive full copies of the parental DNA
What is the process called for the copying of DNA
semi-conservative replication
Why is the process of DNA being copied called semi-conservative replication
in each new DNA molecule produced, one of the polynucleotide DNA strands (half of the new DNA molecule) is from the original DNA molecule being copied
What happens to the other half of a newly copied DNA molecule as half a DNA molecule has been copie
The other polynucleotide DNA strand (the other half of the new DNA molecule) has to be newly created by the cell
the new DNA molecule has conserved half of the original DNA and then used this to create a new strand
What does retaining one original strand of DNA ensure
there is genetic continuity (i.e. genetic information is conserved) between generations of cells
Genetic continuity
ensures that the new cells produced during cell division inherit all t
Why is genetic continuity important
cells in our body are replaced regularly and therefore we need the new cells to be able to do the same role as the old ones
Mitosis
when a parent cell divides to produce two genetically identical daughter cells
Why must the number of DNA molecules in the parent cell be doubled before mitosis takes place
each daughter cell contains the same number of chromosomes as the parent cell
What does DNA replication take place
DNA replication occurs during the S phase of the cell cycle (which occurs during interphase, when a cell is not dividing)
Process of semi-conservative replication 1
The enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between the base pairs on the two antiparallel polynucleotide DNA strands to form two single polynucleotide DNA strands
Process of semi-conservative replication 2
Each of these single polynucleotide DNA strands acts as a template for the formation of a new strand made from free nucleotides that are attracted to the exposed DNA bases by base pairing
Process of semi-conservative replication 3
The new nucleotides are then joined together by the enzyme DNA polymerase which catalyses condensation reactions to form a new strand
Process of semi-conservative replication 4
The original strand and the new strand join together through hydrogen bonding between base pairs to form the new DNA molecule
What do the extra phosphates in the nucleus of DNA do
In the nucleus, there are free nucleotides which contain three phosphate groups
These nucleotides are known as nucleoside triphosphates or ‘activated nucleotides’
The extra phosphates activate the nucleotides, enabling them to take part in DNA replication
How does the enzymes DNA polymerase synthesise new DNA strands from the two tempate strands
It does this by catalysing condensation reactions between the deoxyribose sugar and phosphate groups of adjacent nucleotides within the new strands, creating the sugar-phosphate backbone of the new DNA strands
What are the free nucleotides in the nucleus known as
nucleoside triphosphates or ‘activated nucleotides’
What do the bases of the free nucleoside triphosphates do
align with their complementary bases on each of the template DNA strands
What does DNA polymerase do after synthesising new DNA strands
DNA polymerase cleaves (breaks off) the two extra phosphates and uses the energy released to create the phosphodiester bonds (between adjacent nucleotides)
What forms between the complementary base pairs of the template and new DNA strands
HYDROGEN BONDS
Examples of mistakes occurring in replication
Bases being inserted into the complementary strand in the wrong order
An extra base being inserted by accident
A base being left out by accident
What can mistakes in the process of semi-conservative replication lead to
the occurrence of random, spontaneous mutations (i.e. errors in the genetic code)
Gene
a sequence of nucleotides that forms part of a DNA molecule (one DNA molecule contains many genes)
What does the sequence of nucleotides (the gene) code for
the production of a specific polypeptide (protein)
What are protein molecules made up of
A series of amino acids bonded together
What does the shape and behaviour of a protein depend on
depends on the exact sequence of these amino acids
What is the initial sequence of amino acids known as
The primary structure of the protein molecule
Why do genes in DNA molecules control protein structure (and as a result protein function)
they determine the exact sequence in which the amino acids join together when proteins are synthesised in a cell
What is the sequence of DNA nucleotide bases found within a gene determined by
A triplet code
Start and stop signals
tell the cell where individual genes start and stop
As a result, the cell reads the DNA correctly and produces the correct sequences of amino acids (and therefore the correct protein molecules) that it requires to function properly
What does genetic code being non-overlapping mean
Each base is only read once in which codon it is part of
Why is the code said to be degenerate
multiple codons can code for the same amino acids
What does the degenerate nature of the genetic code lead to
can limit the effect of mutations
Codon
A sequence of three consecutive nucleotides in a DNA or RNA molecule that codes for a specific amino acid
Each triplet within the mRNA code
The same triplet codes code for the same amino acids in all living things (meaning that genetic information is transferable between species)
What does this lead to
The universal nature of the genetic code is why genetic engineering (the transfer of genes from one species to another) is possible
What is complementary to the codons on mRNA
The tRNA molecules that transfer amino acids possess anticodons which are complementary to the codons on mRNA
Transcription
DNA is transcribed and an mRNA molecule is produced
Ranslation
mRNA (messenger RNA) is translated and an amino acid sequence is produced
Two stages of protein synthesis
Transcription and translation
Where does transcription occur
This stage of protein synthesis occurs in the nucleus of the cell
Process of transcription 1
Part of a DNA molecule unwinds (the hydrogen bonds between the complementary base pairs break)
Process of transcription 2
The exposed gene can then be transcribed (the gene from which a particular polypeptide will be produced)
Process of transcription 3
A complimentary copy of the code from the gene is made by building a single-stranded nucleic acid molecule known as mRNA (messenger RNA)
Process of transcription 4
Free RNA nucleotides pair up (via hydrogen bonds) with their complementary (now exposed) bases on one strand (the template strand) of the ‘unzipped’ DNA molecule
Process of transcription 5
The sugar-phosphate groups of these RNA nucleotides are then bonded together (by phosphodiester bonds) by the enzyme RNA polymerase to form the sugar-phosphate backbone of the mRNA molecule
Process of transcription 6
When the gene has been transcribed (when the mRNA molecule is complete), the hydrogen bonds between the mRNA and DNA strands break and the double-stranded DNA molecule re-forms
Process of transcription 7
The mRNA molecule then leaves the nucleus via a pore in the nuclear envelope
Template strand
Used to produce mRNA molecule, Pairs with base of RNA nucleotides
Coding strand
The other strand which doesn’t pair with a strand of DNA
Why does mRNA molecule contain the exact same sequence of nucleotides as the DNA coding strand
Because the mRNA is formed by complementary pairing with the DNA template strand
Where does translation occur
Cytoplasm of the cell
What is ribosomal RNA
stable molecule that allows mRNA to attach to the ribosome and is aligned correctly ready for the synthesis of the polypeptide chain
What does the cytoplasm contain
there are free molecules of tRNA (transfer RNA)
What happens during transcription
A molecule of mRNA is made in the nucleus
What happens during translation
Amino acids join together to form a polypeptide chain
Process of translation 1
mRNA attaches to a ribosome and transfer RNA collects amino acids from the cytoplasm and carries them to the ribosome. tRNA is a single stranded molecule with a binding site at one end thus it can only carry one type of amino acid, and a triplet of bases at the other
Process of translation 2
tRNA attaches itself to mRNA by complementary base pairing - two molecules attach to mRNA at a time
Process of translation 3
The amino acids attached to two tRNA molecules join by a peptide bond and then tRNA molecules detach themselves from the amino acids, leaving them behind
Process of translation 4
This process is repeated thus leading to the formation of a polypeptide chain until a stop codon is reached on mRNA and ends the process of protein synthesis
