4. Nucleic acids Flashcards
What are nucleotides?
They are biological molecules and the monomers of nucleic acids (DNA and RNA)
What is the structure of nucleotides?
There is a five-carbon (pentose) sugar bonded to a phosphate group and a nitrogenous base.
What is the pentose sugar in the nucleotide for RNA?
ribose
What is the pentose sugar in the nucleotide for DNA?
deoxyribose
What is a phosphorylated nucleotide?
A nucleotide that contains more than one phosphate group.
What are the 4 nitrogenous bases and what are they called as part of a nucleotice?
adenine = adenosine cytosine = cytosine guanine = guanosine thymine = thymosine
What is it called when there is 1 phosphate group?
monophosphate
What is it called when there is 2 phosphate groups?
diphosphate
What is it called when there is 3 phosphate groups?
triphosphate
Where is is DNA found?
The nuclei of all eukaryotic cells, the cytoplasm of prokaryotic cells and inside some types of viruses.
What is the structure of DNA?
A polymer made up of repeating monometric units (nucleotides).
A molecule of DNA consists of 2 polynucleotide strands.
The 2 strands run in different directions, they are antiparellel.
What is the structure of a phosphate group?
It contains a phosphorus atom bonded with a single covalent bond to 3 hydroxyl (OH) groups and a double covalent bond with 1 oxygen atom.
What is the structure of ribose?
A pentose sugar with a hydroxyl (OH) group on carbon 1, 2, 3 and 5
What is the structure of deoxyribose?
A pentose sugar with a hydroxyl (OH) group on carbon 1, 3 and 5 but a hydrogen atom on carbon 2.
How does the phosphate group bond to the pentose sugar in a nucleotide?
Through a condensation reaction.
The hydroxyl (OH) group on carbon 5 of the pentose sugar and the hydrogen from one of the hydroxyl groups on the phospate group bond to release a water molecule (H20).
This forms the covalent bond.
How does the nitrogenous base bond to the pentose sugar in a nucleotide?
Through a condensation reaction.
The hydroxyl (OH) group on carbon 1 of the pentose sugar and the hydrogen from the nitrogenous base bond to release a water molecule (H20).
This forms the covalent bond.
What is a purine?
A nitrogenous base with two rings.
Adenine and Guanine.
What is a pyrimidine?
A nitrogenous base with one ring.
Thymine, Cytosine and Uracil.
How do the two antiparallel DNA strands join together?
By hydrogen bonds between the two nitrogenous bases.
Which nitrogenous bases bond together?
Adenine and Thymine with two hydrogen bonds
Guanine and cytosine with three hydrogen bonds
Why do purines always bond with pyrimidines?
Because it means that each pair has 3 rings (2 from the purine and 1 from pyrimidine).
How is DNA organised in eukaryotic cells?
The majority of the DNA is in the nucleus.
The DNA molecules are wound around histone proteins into chromosomes.
Each chromosome is a molecule of DNA.
There is also a loop of ‘naked’ DNA inside mitochordria and chloroplasts.
How is DNA organised in prokaryotic cells?
DNA is in a loop within the cytoplasm, not enclosed in a nucleus.
It is not wound around histone proteins.
It is described as naked.
What has to happen before cell division?
During interphase, DNA has to be copied so that each new daughter cell receives the full set of instructions.
How does DNA replicate?
By semi-conservative replication…
1) Unwinding
2) Unzipping- hydrogen bonds between nucleotides are broken.
3) Free phosphorylated nucleotides in the nucleus are bonded to the exposed bases.
4) Leading strand is synthesised continuously. Lagging strand is synthesised in fragments then later joined.
5) Phosphodiester bonds form between the sugar of one nucleotide and the phosphate group of the next.
What enzymes are involved with DNA replication?
1) Unwinding is catalysed by gyrase enzyme.
2) Unzipping is catalysed by DNA helicase.
3) Formation of phosphodiester catalysed by DNA polymerase.
4) Synthesis of lagging strand catalysed by ligase enzyme.
What is the result of semi-conservative replication?
2 DNA molecules, identical to each other and to the parent molecule.
Each of these molecules contains one old strand and one new strand.
How is RNA different from DNA?
The sugar in the nucleotides of RNA is ribose, not deoxyribose.
The nitrogenous base uracil (a pyrimidine) replaces thymine.
The polynucleotide chain is single-stranded.
The polynucleotide chain is shorter.
What are the 3 forms of RNA?
messenger (mRNA)
transfer (tRNA)
ribosomal (rRNA)- Used to make ribosomes and made in the nucleolus.
How can genes carry out their function?
Within each gene there is a sequence of DNA base triplets that determines the amino acid sequence (primary structure) of a polypeptide.
This allows it to fold correctly into its tertiary structure, enabling it to carry out its function.
What is transcription and translation?
Instructions inside the genes on chromosomes cannot pass out of the nucleus so a copy of each gene has to be transcribed (copied) into a length of mRNA.
This can pass out of the nucleus to the ribosome where the coded instructions are translated and the protein is assembled from amino acids.
What are the stages of transcription?
1) The gene unwinds and unzips
2) Hydrogen bonds between the base pairs break.
3) Temporary hydrogen bonds form between RNA nucleotides and the nucleotides of the DNA’s template strand.
4) A length of RNA that is complementary to the template strand of the gene is produced- This is an exact copy of the coding strand.
5) The mRNA passes out of the nucleus, through the nuclear envelope, and attaches to the ribosome.
Where are transfer RNA molecules made?
Made in the nucleolus and pass out of the nucleus into the cytoplasm
What is the structure of transfer RNA molecules?
A single RNA strand
Hydrogen bonds between the bases maintains the structure.
At one end is an anticodon (triplet of bases) that are complementary to the codon on the mRNA
At the other end is another triplet of bases which bind to a specific amino acid which will be bound to the mRNA.
What is the funtion of transfer RNA?
They bring the amino acids to the ribosome and find their complementary place on the mRNA molecule.
Why is the genetic code described as universal?
Because all living organisms have the same triplet of DNA bases that code for the same amino acid.
Why is the genetic code described as degenerate?
Because for almost all amino acids there is more than one base triplet.
This reduces the effect of point mutations, as a change in one base could produce 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. If a bases is added or deleted, it causes a frame shift. Every base triplet after that, and hence every amino acid coded for, is changed.
