Module 2 - Nucleic Acid Flashcards
What are nucleotides
Biological molecules that participate in all biochemical processes, made of a phosphate group linked to C5 or C3 of the pentose sugar attached to a base
Monomers that form nucleic acid, DNA and RNA
What are phosphorylated nucleotides?
Nucleotides that contain more than one phosphate group; eg
ADP (adenosine diphosphate) and ATP ( adenosine triphospate)
Where is DNA found
DNA is found in the nuclei of all eukaryotic cells, within the cytoplasm of prokaryotes
Explain the structure of DNA
Polymer made of repeating monomeric units called nucleotides
Consists of two polynucleotide strands (antiparallel)
One of four nitrogenous bases: adenine, thymine, cytosine and guanine
Bond between phosphate and sugar is a phosphodiester bond (condensation reaction)
Name two purines I
Adenine and guanine ( two rings)
Name two pyramidines
Thymine and cytosine (one ring)
Explain hydrogen bonds in reference to the four bases
Pyramidines are always paired with purines, so Adenine is with Thymine and Cytosine with Guanine
Adenine and Thymine pair by means of 2 hydrogen bonds
Guanine and Cytosine pair by means of 3 hydrogen bonds
What shape is DNA in?
A double Helix
How does the sugar phosphate backbone form?
The 5’ end of the molecule is where the phosphate group is attached to the fifth carbon of the pentose sugar
The 3’ end of the molecule is where the phosphate group is attached to another phosphate from the nucleotide below
How is DNA organised within cells
Eukaryotes: DNA content (genome) is in nucleus
DNA tightly wound around special histone proteins into chromosomes
Prokaryotes: DNA in loops within cytoplasm
Described as naked
What is semi conservative replication?
To make a new copy:
Molecules unwind - double helix untwists, catalysed by gyrase enzyme
Molecules unzip - hydrogen bonds between bases are broken, catalysed by DNA Helicase, resulting in exposed bases and two dna strands
Free phosphorylated nucleotides bond to bases (complementary)
DNA polymerase catalyses new bases in 5’ to 3’ direction using unzipped dna as template
What are the leading strand and lagging strand?
Leading strand is in the 5’ to 3’ direction so is continuously synthesised
Lagging strand is in the 3’ to 5’ directions so cannot be continuous but is fragmented (discontinuous), later joined catalysed by ligase enzyme
Why is it called semi conservative replication?
This is because each molecule contains one old strand and one new strand, they are identical to their parent and to each other
What are mutations?
Errors that are made during replication eg wrong nucleotide is inserted
This can change the genetic code (point mutation)
Not all are harmful and some give advantages like helping animals hide in winter (changing fur to white like snow)
How does the body prevent mutations occurring
There are enzymes that proof read and edit out incorrect nucleotides, reducing the rate of mutations being produced
How is RNA different from DNA structurally?
Sugar molecule is ribose Uracil replaces thymine Polynucleiotide is single stranded Shorter chain Three forms of RNA - messenger (mRNA), transfer (tRNA) and ribosomal (rRNA)
What are genes?
Genes are proteins that contain codes which determine the sequence of amino acids in a particular polypeptide/protein
What are the structures of genes?
Sequence of DNA base triplets that determine amino acid sequence (primary structure) so it folds correctly
Instructions in genes cannot pass out the nucleus thus must be transcribed into a length of mRNA - codons (base triplets) pass out nucleus to ribosomes ensuring the instructions are translated and the protein is assembled properly
Describe the nature of the genetic code
Near universal as all living things have the same triplet copse of dna bases codes for the same amino acid
Described as degenerate, as for many there are more than one base triplet reducing point mutations
Described as non overlapping, read starting from a fixed point and bases added or deleted causes a shift changing the amino acid sequence
Transcription n Translation
Transc-
- gene unzips
- hydrogen bonds between complementary nucleotide bases break
- RNA Polymerase catalysed formation of temporary hydrogen bonds between RNA nucleotides and their complementary unpaired DNA bases
- A and T, C and G, U and A
- length of RNA complementary to the template strand is produced
- mRNA passes out of nucleus through the nuclear envelope and attaches to a ribosome
What is tRNA?
- tRNA molecules are made in nucleus
- single stranded polynucleotides twisted into a hairpin shape
- has anticodons on one end and amino acids on the other
- found in the cytoplasm
Translation?
- tRNA molecule brings amino acids and finds its place when the anticodon bonds by temporary hydrogen bonds to the complementary codon on the mRNA molecule
- as ribosome moves along length of mRNA, reads code and when two amino acids are beside each-other a peptide bond forms between them
- ATP is needed
- after polypeptide has been made, mRNA breaks down, molecules can b recycled into new lengths of mRNA with different codon sequences
- new polypeptide is helped by chaperone proteins in the cell to fold into 3D shape
