| Definition of nucleic acids? (4) | genetic material made of recurring monomeric units (nucleotides): a phosphate group (circle)
5-carbon pentose sugar (pentagon)
nitrogenous base (A, C, G, T) |
| Draw a nucleotide (3) | 5-carbon sugar , phosphate group and a nitrogenous base (A, T, G , C)
Nitrogenous base attached to 1' carbon atom
Phosphate base attached to 5' carbon atom |
| How are the nucleotides bonded? | covalently bonded |
| Definition of DNA (2) | deoxyribonucleic acid: stable double stranded form = stores genetic blueprint of cells
made up of polymers of nucleotides |
| Definition of RNA | ribonucleic acid: versatile single stranded form = transfers genetic info for decoding from nucleus to cytoplasm
made up of polymers of nucleotides |
| what is produced with the phosphodiester bond? | water is produced when there is a phospho bond between two nucleotides |
| What are the 5 different nitrogenous bases? | Adenine, Thymine, Guanine Cytosine, Uracil |
| how are the nucleotides linked together? | linked into a strand by condensation reactions which forms long polynucleotides |
| in what order are the nucleotides formed? | 5 to 3 |
| how are the nitrogenous bases bonded? | hydrogen bonding |
| number of bonds between AT and GC? | AT = 2 GC = 3 |
| what pairs do the nitrogenous bases form? | AT and GC |
| what is the structure of DNA? (4) | sugar phosphate backbones
strands run in opposite directions (antiparallel)
made up of polynucleotide strands
double helix |
| differences between RNA and DNA? (3) | DNA = deoxyribose, ATGC, double stranded
RNA = ribose, AUGC, single stranded |
| What did Watson and Crick propose about the DNA molecule? (4) | Made models of DNA based off of findings from other researchers:
bond angles + molecular distances by Pauling
DNA is made of nucleotides (sugar, phosphate and base)
equal number of purines (A + G ) and pyrimidines (T + C)
organized into a helical = Franklin |
| What was included in their DNA model? (3) | antiparallel and form a double helix
complementary base pairing (AT GC)
outer edges of bases exposed for replicative and transcriptional proteins |
| problems with earlier models of the DNA molecule? | triple helix
bases on the outside and sugar-phosphate residues in center
bases didn't show complementarity |
| How did Rosalind Franklin contribute to the DNA molecule? | X-ray crystallography data that showed the DNA arrangement as a helical structure
shared without Franklin's permission but helped a lot to the final model of DNA |
| What do mRNA do? (messenger) | transcripts a gene copy that encodes for a specific polypeptide |
| What is an rRNA? (ribosomal) | in ribosomes for catalyctic activity |
| What is a tRNA? (transfer) | carries PP subunits (AA) to ribosome for synthesis |
| Outline DNA replication (3) | DNA is copied during the formation of new cells in the nucleus before cell division (with enzymes) |
| Outline transcription (3) | DNA codes for RNA transcripts with the mRNA continuously in the nucleus (with enzymes) |
| outline translation (3) | mRNA transcripts code for protein production continuously after transcription in the cytoplasm (With ribosomes) |
| Why is DNA replication a semi-conservative process? | Bec when new DNA molecules form they're made of one original strand and one new strand |
| How does the semi-conservative method work? (3) | bec each base can only pair with its complementary base pair (AT, GC) = base sequence is conserved during replication
as each new strand formed will be identical to the original strand which separates from the template |
| What were the three models to explain how the new molecules formed? | conservative model: entire new molecule from original DNA molecule
Semi-conservative model: ever new molecule comes from one new strand and one template strand
dispersive model: new molecules made from new and old DNA segments |
| Describe the Meselson-Stahl experiment (7) | 2 radioactive isotopes of N were used during replication (15N and 14N)
DNA molecules were first incorporated with 15N and then replicated in the presence of the 14N
(nitrogen makes up DNA and can be either 15N or 14N)
DNA samples were separated to see the composition of DNA in replicated molecules
1st division: DNA molecules had both 15N and 14N = disproves conservative
2nd division: Some molecules only had 14N = disproves dispersive
= supports the semi conservative model |
| What does helicase do? (3) | unwinds double helix to separate the 2 PN strands
by breaking hydrogen bonds between complementary base pairs
the separated PN strands = templates for new strand synthesis |
| What does DNA polymerase (III) do? | makes new strands from 2 template strands
free deoxynucleoside triphosphates aligns with complementary base pair with hydrogen bonding
covalently joins the DNA nucleotides together to form a new strand (phosphodiester bond) |
| What is PCR? (polymerase chain reaction) (3 steps) | artificial method of replication to make large quantities of a DNA sequence. happens in a thermal cycler at different temps
1) Denaturation: heat separates strands (95 degrees)
2) Annealing: cooled so primers make copying sequence (55 degrees)
3) Elongation: TAQ polymerase copies sequence (72 degrees)
= 1 billion copies |
| What does DNA replication do? (2) | Semi conservative process whereby DNA is copied to create identical sister chromatids before cell division.
The key enzymes used are: Helicase (separate DNA strands) and DNA polymerase (copies new strands) |
| Describe the process of polymerisation (w DNA polymerase (III) (4) | new nucleotides align with complementary pairs as (deoxynucleoside triphosphates)
DNA pol III cleaves 2 phosphates = releases energy
energy is used by enzyme = covalent phosphodiester bond w/ nucleotide chain
5' - 3' direction ON NEW STRAND |
| What are codons? (2) | How the mRNA is read by ribosomes as triplets of bases = each triplet = 1 AA
order of codons = order of AA in a PP chain |
| What is the genetic code? (5) | rules by which mRNA sequences are converted into protein
identifies the corresponding AA for each codon
64 codon possibilities
Coding region always begins with the START codon (AUG) and ends with the STOP codon
key features:
Universality: all organisms use the same code
Degeneracy: more than 1 codon can code for the same AA (only 20 AA) |
| Translation overview | MRNA goes to
Ribosome, which reads sequence as
Codons recognised by
Anticodons on
TRNA which carries
AA which joins with
PP bonds to form
Polypeptides |
| Why is genes transferrable between species? | Because the same codons code for the same AA in all living things |
| where has gene transferability been used? (6) | to produce human insulin in bacteria for mass production
gene for insulin production is removed from a human cell
spliced and put in a plasmid vector = autonomous replication and expression
then put in a bacterial cell (E-Coli)
the transgenic bacteria is then cultured in a fermentation tank (increase numbers)
bacteria= produces human insulin = used for diabetics |
