Nucleic acids

Question 1

Nucleic acids?

Answer 1

• ‘info carrying’ molecules
• 2 main types = RNA & DNA
• monomer: nucleotides, polymer: nucleic acids

Question 2

Structure of RNA?

Answer 2

• ribonucleic acid
• polymer of nucleotide formed of: ribose (alw) (pentose sugar), nitrogenous base & phosphate group
• bases: adenine, guanine, cytosine & Uracil
• 3 main types: messenger, ribosomal, transfer
• single stranded generally

Question 3

mRNA?

Answer 3

• a copy of 1 gene from DNA
• created in nucleus - leaves nucleus to carry copy of genetic of gene - to ribosome in cytoplasm
• DNA too large to leave nucleus (to provide genetic code to make protein) & would be at risk of damage by enzymes and so - destroying genetic code permanently
• much shorter (as only length of 1 gene)
• short lived - only temporarily needed - by time enzymes could break down - would’ve alr carried out function
• single stranded
• every 3 bases (in sequence) code for specific amino acid aka codons

Question 4

tRNA?

Answer 4

• only in cytoplasm
• single stranded but folded to create shape like cloverleaf - held in place by H bonds
• function: to attach to 1 of 20 amino acids & transfer ts to ribosome to create polypeptide chain
• specific amino acids attach to specific tRNA molecules & bring to mRNA - determined by complimentary base pairing between codon on mRNA & anticodon on tRNA
• tRNA has 3 complementary bases to codon - - how mRNA codes

Question 5

rRNA?

Answer 5

• combines w protein to make ribosomes
• makes up the bulk of ribosomes

Question 6

DNA?

Answer 6

• deoxyribonucleic acid
• double helix structure - made up of 2 polynucleotide strands
• molecules r extremely long
• monomer: nucleotide: deoxyribose (alw) (pentose sugar) (pentagon), nitrogenous base (rectangle) & phosphate group (circle)
• bases either: A,T,C or G

Question 7

Function of DNA?

Answer 7

• codes for sequence of amino acids in primary structure of a protein - which determines final 3D structure & function of protein
• essential that cells contain copy of this genetic code & that it can be passed onto new cells w/o being damaged

Question 8

Polynucleotides?

Answer 8

• polymer of nucleotides
• created via condensation reactions between deoxyribose sugar & phosphate group - forming phosphodiester bond…
• r strong covalent bonds & so - help ensure genetic code isn’t broken down
• polynucleotide has a sugar-phosphate backbone - describes the strong covalent bonds between sugar + phosphate groups that hold polymer together

Question 9

How are the 2 polynucleotide strands in DNA molecules held together?.

Answer 9

• DNA has antiparallel strands - run in opp directions
• base pairs joined tgt by H bonds - how double helix created as 2 chains twist
• bases on opposite strands pair up by complementary base pairing - C can only form H bonds w G, A can only bond w T
• A & T - form 2 H bonds between e/o
• C & G form 3 H bonds

Question 10

DNA v RNA?

Answer 10

monomers:
- DNA contains T, RNA: U instead
- DNA: pentose sugar: deoxyribose, RNA: ribose

polymers:
- DNA: much larger (cos contains all genes/entire genome), RNA: much shorter (only length of 1 gene)
- DNA: double stranded, RNA: single stranded

Question 11

How DNA structure relates to its function?

Answer 11

• Stable structure: due to sugar-phosphate backbone (held tgt by phosphodiester/covalent bonds) - protects bases (genetic code) & due to double helix (carries genetic code) & many H bonds r strong tgt
• 2 strands held tgt by H bonds - allowing strands to be separated during DNA replication & protein synthesis (for genes to be read) (by breaking H bonds)
• double stranded so replication can occur using 1 strand as template…
• weak H bonds for easy unzipping of 2 strands during replication
• large molecule - carry huge amount of genetic info
• function of gene/protein made from gene depends on base sequence
• complementary base pairing means DNA replicated accurately so - identical copies made

Question 12

DNA replication

Answer 12

• before cells divide - in interphase
• so that there’s a copy for the new cell
• semi-conservative: daughter - 1 strand from parental DNA & 1 strand newly synthesised

Question 13

Step-by-step process of semi-conservative DNA replication?

Answer 13

1. enzyme: DNA helicase, causes DNA double helix to unwind and separate into two strands by breaking the hydrogen bonds between complementary base pairs, exposing the bases.
2. Both separate strands then act as a template for DNA replication to occur.
3. Free activated DNA nucleotides (in the nucleoplasm) are attracted to and hydrogen bond to their complementary bases on the exposed template strands by complementary base pairing.
4. The newly added nucleotides are then joined together by the enzyme DNA polymerase, which catalyses the formation of phosphodiester bonds, between adjacent nucleotides.
5. This results in two identical DNA molecules being produced, each of which contains one of the original DNA strands and one newly synthesised DNA strand (semi-conservative)..

Question 14

5’ to 3’?

Answer 14

• nucleotides can only be added in 5’ to 3’ prime direction cos: DNA polymerase can only attach nucleotides to OH group on 3’ carbon

Question 15

Background info on Meselson & Stahl?

Answer 15

1. DNA bases are nitrogenous
2. N has 2 isotopes - 14N (lighter) & 15N (heavier)
3. Bacteria take in N isotopes to make new DNA nucleotides…
   - bacteria grown in medium - will take in any N from growth medium & incorporate it into any new DNA they make during DNA replication (nucleotides)
   - 14N - hv DNA only containing ts isotope & be lighter
   - bacteria grown in 15N - hv DNA - heavier