Nucleic Acids Flashcards
What are nucleotides?
Biological molecules that participate in most biochemical processes
Form the monomers of nucleic acids, DNA and RNA
May be components of many coenzymes
What is a phosphorylated nucleotide?
A nucleotide that contains more than one phosphate group
What is the nucleotide pentose sugar in
1 DNA and
2 RNA?
1 Ribose
2 Deoxyribose
What can nucleotides help regulate?
Many metabolic pathways
What is DNA?
A nucleic acid - deoxyribose nucleic acid
The material that carries coded instructions used in the development and functioning of all known living organisms
One of the macromolecules that make up the structure of living organisms
Where is DNA found?
In the nuclei of all eukaryotic cells
Within the cytoplasm of prokaryotic cells
Inside some types of viruses
What is the structure of DNA?
A polymer made up of nucleotides
Two polynucleotide strands running in opposite directions (antiparallel)
Phosphate group
A five-carbon sugar(deoxyribose)
1/4 nitrogenous bases (adenine, guanine, thymine, cytosine)
Long - can carry a lot of genetic info
What are purines and pyrimidines?
Nitrogenous bases that differ in each nucleotide
Purine - adenine or guanine
Pyrimidine - thymine or cytosine
What is the different between a purine and pyrimidine?
Purine have two carbon-nitrogen rings
Pyrimidine have one carbon-nitrogen ring
What bonds hold together the two antiparallel DNA strands?
Hydrogen bonds
Which purines and pyrimidine always pair up?
Adenine always pairs with thymine
Guanine always pairs with cytosine
How many hydrogen bonds can nucleotides with adenine as the base make with nucleotides with thymine as the base?
Two hydrogen bonds
How many hydrogen bonds can nucleotides with guanine as the base make with nucleotides with cytosine as the base?
Three hydrogen bonds
What gives a DNA molecule it’s stability?
The double helix formed from the two antiparallel DNA strands twisting around each other
What is the sugar-phosphate backbone?
The chain formed from the nucleotides joining up between the phosphate group of one and the sugar of another via a phosphodiester bond
How is DNA organised in eukaryotic cells?
Majority of the genome is in the nucleus
Each molecule of DNA is tightly wound around histone proteins into chromosomes
There’s also a loop of DNA without the histone proteins inside mitochondria and chloroplasts
What is meant by genome?
All of the DNA content within a cell
How is DNA organised in prokaryotic cells?
Within the cytoplasm in a loop, not enclosed in a nucleus
Not wound around histone proteins, described as naked
What does all DNA carry within every cell of an organism?
The coded instructions to make and maintain that organism
Why does DNA have to be copied every time a cell divides?
So that each new daughter cell receives the full set of instructions
What is semi-conservative replication?
How DNA replicates, resulting in two new molecules, each of which contains one old strand and one new strand
What does each DNA molecule do to make a new copy of itself?
The double helix is untwisted a bit at a time
The hydrogen bonds between the nucleotide bases are broken
Resulting in two single strands of DNA with exposed nucleotide bases
What happens to the DNA after it unwinds and unzips?
Free phosphorylated nucleotides are bonded to the exposed bases
DNA polymerase catalyses the addition of the new bases to the strands of DNA, using each strand of unzipped DNA as a template
The unzipped strand is synthesised continuously
Hydrolysis of activated nucleotides, to release extra phosphate groups, supplies the energy to make phosphodiester bonds between the deoxyribose of one nucleotide and the phosphate group of the next
What is the product of DNA replication?
Two DNA molecules, identical to each other and to the parent molecule
How are the loops of DNA in prokaryotes and inside mitochondria and chloroplasts replicated?
Also semi-conservatively
A bubble sprouts from the loop and this unwinds and unzips, and then complementary nucleotides join to the exposed nucleotides
Eventually the whole loop is copied
What are mutations?
Errors that may occur during DNA replication
How can mutations occur during DNA replication?
If the wrong nucleotide is inserted
What could happen as a result of a mutation?
The genetic code could change
How can the rate of mutations be reduced?
There can be enzymes during the replication process that can proofread and edit out any incorrect nucleotides
What is an allele?
Different versions of a particular gene
How can some mutations be advantageous?
If they provide a survival advantage
How is RNA structurally different from DNA?
The sugar molecule is ribose
The nitrogenous base uracil replaces thymine as a pyrimidine base
Polynucleotide chain is usually single-stranded and shorter
There are three different forms
What are the 3 forms of RNA?
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
What is a gene?
A length of DNA that contains a code determining the sequence of amino acids in a particular polypeptide or protein
What makes up a polypeptide’s primary structure/determines the sequence of amino acids in a polypeptide or protein?
A sequence of DNA base triplets within each gene
Why is there a need for transcription?
Because as genes are inside the nucleus and proteins are made in the cytoplasm, the instructions inside the genes have to be transcribed into a length of mRNA as they cannot pass out of the nucleus
What are base triplets called when in the form of mRNA?
Codons
What is the nature of the genetic code?
It is universal, degenerate and non-overlapping
Why is the genetic code described as universal?
Because in most living organisms, the same triplet of DNA bases codes for the same amino acid
Why is the genetic code described as degenerate?
Because for most amino acids there is more than one base triplet
How can the genetic code being degenerate reduce the effect of mutations?
A change in one base of the triplet could produce another base triplet that still codes for the same amino acid
Why is the genetic code described as non-overlapping?
It is read starting from a fixed point in groups of three bases, separate from the triplet before it and after it - base triplets don’t share their bases
Summarise the process of transcription of a gene into a length of mRNA
A gene unwinds and unzips
Hydrogen bonds between complementary nucleotide bases break
RNA polymerase catalyses the formation of temporary hydrogen bonds between RNA nucleotides and their complementary unpaired DNA bases
A length of RNA complementary to the template strand of the gene is produced
mRNA passes out of the nucleus, through the nuclear envelope, and attaches to a ribosome
Where and how are ribosomes formed?
Formed in the nucleolus in two smaller subunits
They pass out of the nucleus separately through pores in the nuclear envelope
Come together to form a ribosome
Mg ions help bind the two subunits
What is the structure of transfer RNA?
Single stranded polynucleotides that can twist into a hairpin shape
At one end they have a trio of nucleotide bases that recognise and attach to specific amino acids
At the loop of the hairpin there is an anticodon (another triplet of bases) that is complementary to a specific codon of bases on the mRNA
Where are tRNA molecules made?
In the nucleolus
What is translation?
The formation of a protein, at ribosomes, by assembling amino acids into a particular sequence according to the coded instructions carried from DNA to the ribosome by mRNA
Describe the process of translation
tRNA molecules bring the amino acids and find their place when the anticodon binds by temporary hydrogen bonds to the complementary codon on the mRNA molecule
Ribosome moves along the length of mRNA, reading the code - peptide bonds form between adjacent amino acids
mRNA breaks down and can be recycled into new lengths of mRNA with different codon sequences
New polypeptide folds into its tertiary structure in order to carry out its function
What is needed for polypeptide synthesis?
Energy in the form of ATP
What is the amino acids sequence for the polypeptide ultimately determined by?
The sequence of triplets of nucleotide bases on the length of DNA - the gene
