Week 6 - the genetic material

Question 1

DNA - structure

Answer 1

nucleic acid composed of NUCLEOTIDES

• 5 carbon sugar (DEOXYRIBOSE)
• phosphate group (PO4)
• nitrogenous base → adenine, thymine, cytosine, guanine
• free hydroxyl group (-OH) →attached at the 3’ carbon of sugars

Question 2

phosphodiester bond

Answer 2

• bond between ADJACENT nucleotides

- formed between phosphate group of one nucleotide & the 3’ -OH of next nucleotide

Question 3

nitrogenous bases

Answer 3

PYRIMIDE - SINGLE RINGED STRUCTURE → thymine & cytosine

PURINE- DOUBLE RING STRUCTURE → adenine & guanine

Question 4

chargaff rules

Answer 4

• amount of adenine = amount of thymine
• amount of cytosne= amount of guanine
• always equal proportion of purines & pyrimidines

Question 5

DNA helix

Answer 5

• 2 strands are polymers of nucleotides
• phosphodiester backbone- repeating sugar & phosphate units joined by phosphodiester bonds
• consists of two polynucleotide strans wrapped aorund eachother in a double helix

Question 6

DNA genes & inheritance

Answer 6

• nucleic acids STORE & TRANSMIT hereditary info
• sequence of bases along a nucleotide polymer →unique for each gene
• genes:
  → units of inheritance
• program the amino acid sequence of polypeptides and functional RNA species

Question 7

DNA replication

Answer 7

EVERYTIME A SOMATIC CELL DIVIDES, CHROMOSOMAL DNA IS REPLICATED
- DNa replication in cells must be V accurate
- since the two strands of DNA are:
→complimentary , each strand acts as a template for building a new strand during DNA replication

Question 8

DNA replication requirements

Answer 8

• something to copy: PARENT DNA MOLECULE
• something to do the copying: REPLICATION MACHINERY & REPLICATION ENZYMES
• building blokes to make copy: NUCLEOTIDE TRIPHOSPHATES

Question 9

DNA replication - polymerase

Answer 9

DNA polymerase (SYNTHESISES a polymer of nucleotides; in this case - DNA strand)
- matches existing DNA bases w/ complementary nucleotides & links via PHOSPHODIESTER BOND
→ adds new bases to 3’ end of strands
→ SYNTHESISE IN 5’ TP 3’ DIRECTION

RNA primers are removed and replaced w/ DNA later in process

Question 10

Helicase

Answer 10

unwinds parental helix at replication forks

Question 11

single-strand binding protein

Answer 11

binds & spabilises SS DNA until it can be used as a template

Question 12

Topoisomerase

Answer 12

relieves ‘ overwinding’ strain ahead of replication forks by breaking, swivelling & rejoining strands

Question 13

primase

Answer 13

synthesise RNA primer at 5’ end

Question 14

DNA pol III

Answer 14

synthesises new strand, add NT to 3’ of strand

Question 15

DNA pol I

Answer 15

remove RNA NT of primer @ 5’, replace w/ DNA NT

Question 16

DNA ligase

Answer 16

joins 3’ end of DNA that replaces primer to rest of leading strand & joins okazaki fragments

Question 17

lagging strand synthesis

Answer 17

• discontinuous synthesis (Done by DNA Pol III)
• RNA primer made by primase for each okazaki fragmnet
• all RNA primers removed & replaced by DNA (DNA pol I)
• backbone sealed (by DNA ligase)

Question 18

replication - prokaryotic

Answer 18

• E.coli model
• single circular molecule of DNA
• replication begins at one origin of replication
• proceeds in both directions around the chromosome

Question 19

replication eukaryotic

Answer 19

complicated by:

• larger amount of DNa in multiple chromosomes
• linear structure of chromosomes

basinc enzymology is similar to bacterial replication
- reg. new enzymatic activirt for ealing w/ ends only (telomeres)

unable to rep. last sec.. of lagging strands → gradual shortening

Question 20

telomeres

Answer 20

• composed of short repeated sequences of DNA at the ends of chromosomes
• telomerase - enzyme makes telomere of lagging strands useing internal RNA template
• leading strand can be replicated to tghe end
• telomerase developmentally regulated
• relationship between senescence & telomere length
• cancer cells generally show activation of telomeres