Nucleic Acids Flashcards Preview

BIOLOGY AS > Nucleic Acids > Flashcards

Flashcards in Nucleic Acids Deck (40)
Loading flashcards...

Describe nucleic acids.🌟

- two types: DNA + RNA
- have roles in storage + transfer of genetic info, + synthesis of polypeptides (proteins)
- basis for heredity
- made up of the monomers: nucleotides


Describe the structure of nucleotides.🌟

- linked together in chains
- each made of three components: pentose sugar w/ 5 C atoms, phosphate group, + nitrogenous base
(In DNA the sugar is deoxyribose + in RNA it is ribose).


Name the nitrogenous bases, and identify which are purines and which are pyrimidines for DNA.🌟


Purines: adenine + guanine
Pyrimidines: thymine + cytosine

(Remember by Y in pyrimidines matches with Ys in thymine + cytosine, so they are pyrimidines).


Describe DNA and its structure.🌟

- made of 2 polynucleotide chains running in anti parallel directions
- 2 chains held together by H bonds between base pairs (A + T or C + G), like rungs of a ladder, each strand has 5' (prime) phosphate group at one end + 3' (prime) hydroxyl group at other
- has double helix structure
- has sugar phosphate backbone held together by phosphodiester bonds
- confined to nucleus.


Describe the base pairing rules that hold the two polynucleotide strands of DNA's structure together.🌟

- A bonds with T: by 2 hydrogen bonds
- C bonds with G: by 3 hydrogen bonds

- this known as complimentary base pairing
- these rules mean a small pyrimidine base always bonds to larger purine base to maintain constant distance between DNA backbones, resulting in parallel polynucleotide chains


Describe DNA in Euakaryotic cells.

- most DNA held in nucleus (genome)
- also have loop of DNA in mitochondria + chloroplasts
- DNA tightly wound around histone proteins into chromosomes


Describe DNA in Prokaryotic cells.

- DNA in a loop in cytoplasm (nucleoid)
- also contain plasmids
- not associated w/ histones - it is 'naked'


Describe DNA in viruses.

- a loop of 'naked' DNA


Describe the process of the synthesis and breakdown of polynucleotides by the formation and breakage of phosphodiester bonds (DNA replication). (SEMI CONSERVATIVE)🌟

- DNA molecule unwinds, catalysed by gyrase enzyme
- DNA molecule unzips as H bonds between nucleotide bases are broken, catalysed by DNA Helicase, resulting in 2 single strands of DNA w/ exposed nucleotide bases
- free phosphorylated nucleotides in nucleoplasm are bonded to exposed bases
- DNA polymerase catalyses addition of new nucleotide bases to single DNA strands in 5' to 3' direction, using each single strand as a template
- hydrolysis of activated nucleotides, to release extra phosphate groups, supplies energy to complete new molecule by making phosphodiester bonds between deoxyribose sugar of one nucleotide and phosphate group of the next nucleotide
- leading strand is synthesised continuously, but lagging strand is synthesised discontinuously in okazaki fragments, these later joined, catalysed by Ligase enzymes
- product of replication is 2 DNA molecules, identical to each other + to parent molecule


Describe a practical experiment into the purification of DNA by precipitation.🌟

- swish sports drink around in mouth vigorously for 2 mins, also scrape inside of cheeks w/ teeth gently to collect cheek cells in drink
- spit sports drink + cheek cell solution back into small paper cup, pour into test tube until about one-third full
- add washing up liquid to container (this breaks down fats in plasma membranes) until half full, place bung on + mix gently but avoid causing bubbles from soap
- add a few drops of pineapple juice (to breakdown cells within enzymes) repeat gentle mixing
- trickle a small amount of ethanol into test tube (to precipitate out DNA so you can see it) so alcohol forms a floating layer on top of solution
- set test tube aside for one min
- put a skewer gently into test tube sotip touches band of white gooey material suspended between layers you should see
- carefully twirl skewer (as DNA has double helix structure) in one direction only, so material winds around so can lift it out through alcohol layer to look more closely


Describe ADP and ATP.🌟

- phosphorylated nucleotides
- ADP (adenosine diphosphate) contains base: adenine, sugar: ribose + 2 phosphate groups
- ATP (adenosine triphosphate) contains base: adenine, sugar: ribose + 3 phosphate group


Describe the use of ATP.🌟

- Provides energy for chemical reactions in cell
- Synthesised from ADP
- ADP phosphorylated to form ATP + phosphate bond is formed, which stores energy
- When this energy needed by a cell, ATP broken back down into ADP + inorganic phosphate
- energy then released from phosphate bond + used by cell.


Describe the function of DNA.🌟

Storage of genetic information


Describe the function of RNA.🌟

Transfer of genetic information from DNA to proteins that make enzymes + tissues in body
- protein synthesis


Identify which bases are Purines and which are Pyrimidines for RNA.🌟

Purines: Adenine + Guanine
Pyrimidines: Uracil + Cytosine


State the number of nucleotides in DNA and RNA, roughly.

DNA: up to 300,000,000
RNA: around 300


DNA is a double helix structure with two strands but RNA...🌟

Only has one strand.


Describe RNA generally.🌟

3 diff types:
- mRNA
- tRNA
- rRNA

- can be inside + out of nucleus.


What are the different possible DNA replication models?

- Semiconservative:
actual real model, 2 strands both made of 50% parental 50% new, each split into 2 more strands (so 4 more), one 50 50 of both, + one of complete new strand, so overtime parental strand dilutes

- Conservative model:
not actual model, starts 2 strands, one complete parental + one new, new splits into 2 more new, parental splits into 1 parental 1 new, so overtime parental strand dilutes

- Dispersive model:
not actual model, starts 2 strands both 50 50 parental + new, both split into 2 more 50 50 strands, so 4 more 50 50s in total


Describe a gene.🌟

A length of DNA that codes for a particular protein or polypeptide.


How is DNA read in terms of its code.

DNA is a triplet code.
Read in groups of three bases.
Each triplet is called a codon
1 codon = 1 amino acid.


Describe the genetic code.🌟

- triplet code
- non overlapping, so each gene has fixed stating point + is read in groups of three bases
- each base part of only one codon
- unambiguous: each codon can only code for one specific amino acid
- degenerate: each amino acid can be coded for by at least one, often multiple codons
- almost universal: almost all organisms on Earth use same code.


Describe the start and stop codes for mRNA.

- every mRNA gene starts with an AUG codon.

- START codon: all genes start w/ same codon to produce amino acid methionine.
- STOP codon: all genes end in one of three STOP codons, these not associated w/ the amino acid.


How do you use the codon wheel to decode a codon.🌟

- find first letter of your sequence in the inner circle + work outwards to see corresponding amino acid.


Describe the stage of transcription in protein synthesis.

- happens in nucleus
- converts DNA to mRNA



Briefly describe the two processes in protein synthesis.🌟

- happens in nucleus
- converts DNA to mRNA

- occurs at ribosomes
- converts mRNA to polypeptides


Describe the process of transcription in protein synthesis.🌟

- a gene unwinds + unzips (gyrase + Helicase)
- RNA polymerase forms temporary H bonds between bases in DNA template strand + free RNA nucleotides.

A - U (uracil rather than thymine)
T - A
C - G
G - C

- this produces length of RNA complementary to template strand, so an RNA copy of DNA coding strand
- non-coding sections of mRNA (introns) removed by a spliceosome, leaving coding sections (exons), so leaving mature mRNA.
- mature mRNA leaves nucleus via nuclear pore + travels to a ribosome.


Describe the 3 types of RNA that are involved in translation.🌟

- messengerRNA (mRNA): encodes genetic info + carries it from nucleus to ribosome
- ribosomalRNA (rRNA): together w/ ribosomal proteins, forms part of the ribosome
- transferRNA (tRNA): bring amino acids to ribosome + bind w/ mRNA to create polypeptide chain.


Explain tRNA's structure.

'Met' = amino acid binding site at top
Right angle to left then straight line down to circular shape with three lines off it, one to U, one to A, one to C
'UAC' at bottom = anticodon

The anticodon: triplet of exposed bases that binds to complementary bases on mRNA

Amino acid binding site: on top of tRNA, each tRNA can only carry one specific type of amino acid


Describe the process of translation.🌟

- in cytoplasm, tRNA transferase attaches to amino acids in appropriate tRNA molecule
- mRNA fits into cleft of a ribosome, 6 bases exposed in ribosome at a time
- tRNA complementary to codon no 1 binds
- tRNA complementary to codon no 2 then binds
- the 2 amino acids attached to tRNA molecules in ribosome form a peptide bond
- mRNA moves along one codon, at this point, first tRNA detaches, leaving its amino acid behind, this tRNA can be reloaded + reused
- third tRNA binds to codon 3 on mRNA + another peptide bond forms between amino acids
- this continues until a STOP codon (STOP tRNA does not have an amino acid attached so polypeptide chain ends)
- some proteins need activating by molecules e.g. cyclic AMP (cAMP) to make their 3D shape a better fit for their function.