DNA, protein synthesis (topic 1 + 4)

Question 1

structure of the monomer which is called nucleotide

Answer 1

a pentose
nitrogen-containing organic base A,C,G,T,U
a phosphate group

Question 2

nucleotides joining to each other

Answer 2

weak hydrogen bonds are easily broken, allowing the strands to separate during replication and protein synthesis

(between complimentary bases)

Question 3

how are nucleotides joined

Answer 3

bond between phosphate group of one, and sugar of other
PHOSPHODIESTER BOND

Question 4

hydrogen bonds between nitrogen containing bases

Answer 4

2 between adenine and thymine
3 between cytosine and guanine

Question 5

how are nucleotides joined

Answer 5

condensation reaction
PHOSPHODIESTER bond, between phosphate group of one, and sugar of other

Question 6

RNA

Answer 6

single stranded and relatively short
pentose sugar = ribose
organic bases = AU, CG

Question 7

DNA replication process (semi-conservative replication)

Answer 7

• enzyme DNA helicase breaks hydrogen bonds between complementary bases
• the DNA molecule unwinds and separates into 2 strands
• both polynucleotide chains act as templates which free nucleotides attach to by complementary base pairs
• DNA polymerase joins adjacent nucleotides in a condensation reaction (forms phosphodiester bonds)
• forms 2 new strands of DNA (genetically identical to original strand) (each contain one original strand, one new strand)

Question 8

what is a gene

Answer 8

a section of DNA containing coded information for making polypeptides and functional RNA

enzymes are proteins - due to controlling chemical reactions they are responsible for an organisms development and activities, so along with environmental factors, genes determine the nature and development of all organisms

Question 9

where are genes located

Answer 9

a locus (on a DNA molecule)

Question 10

genetic code (movement in terms of basic protein synthesis)

Answer 10

always remains safe inside the nucleus
- proteins are made outside the nucleus in the cytoplasm so a copy of the genetic code of a gene is made
this copy passes out of the nucleus into the cytoplasm

Question 11

what is a triplet

Answer 11

3 DNA bases that code for a specific amino acid

Question 12

degenerate code and stop code

Answer 12

d: most amino acids are coded for by more than one triplet

s: triplets that code for a stop (marks the end of the polypeptide chain)

Question 13

what are exons and introns

Answer 13

exons: sequences that code for amino acids
introns: non-coding sequences that separate exons in a gene

Question 14

genetic code is universal and non-overlapping

Answer 14

universal: triplets that code for an amino acid are the same in almost all organisms (indirect evidence to evolution)

non-overlapping: each base in a sequence is read only one eg 123 456

Question 15

differences in DNA between prokaryotic and eukaryotic cells

Answer 15

pro: DNA molecules are shorter, not associated with protein molecules, circular DNA, don’t form chromosomes, found in cytoplasm

eu: dna molecules are longer, associated with histones, linear DNA, form chromosomes, found in nucleus (but also in mitochondria and chloroplasts - dna there is like prokaryotic)

Question 16

chromosomes visibility

Answer 16

only visible as distinct structures when a cell is dividing, rest of the time chromatin is widely dispersed throughout the nucleus

Question 17

chromosome structure

Answer 17

one chromosome = two chromatids (because dna has already replicated to give 2 identical dna molecules) joined at a point called the centromere

DNA is highly coiled and held by histones so 2m of dna can be stored in every human cell

Question 18

homologous chromosomes

Answer 18

2 chromosomes that contain the same genes (but not necessarily the same alleles) pair up - look like this ))((

Question 19

allele

Answer 19

different forms of the same gene

Question 20

diagram structure of mRNA and tRNA

Answer 20

mRNA = ribose and phosphate backbone, A U C G, long single helix
tRNA = ribose and phosphate backbone, A U C G, small single strand folded into clover shape, amino acid carried by extended chain, contains the anticodon to mRNA codon

Question 21

how is mRNA adapted for protein synthesis

Answer 21

acts as a template during protein synthesis:
mRNA codons code for amino acids to make polypeptides
easily broken down so only exists when required
single strand able to leave through nuclear pores

Question 22

how is tRNA adapted for its job

Answer 22

anticodon has complementary base pairing to codon on mRNA
carries an amino acid to form the polypeptide chain

Question 23

polypeptide synthesis: transcription

Answer 23

• DNA helicase breaks hydrogen bonds between DNA bases so it uncoils and exposes the organic bases
• free RNA nucleotides line up to ONE strand that acts as a template and pair with complementary bases
• RNA polymerase joins the molecules together by phosphodiester bonds through condensation reactions to form pre-mRNA which then detaches from the dna
• when a stop codon (last 3 bases on mRNA) is reached this ceases

Question 24

protein synthesis: splicing

Answer 24

pre-mRNA is spliced to remove the (non-coding) introns leaving only exons
mRNA contains no introns

when exons rejoin they do so in a variety of different combinations
- so a particular section of DNA can end up coding for a no of proteins depending on arrangement of exons after splicing

Question 25

protein synthesis: translation

Answer 25

once outside the nucleus:
- a ribosome attaches to the starting codon (AUG) at one end of the mRNA molecule
- the tRNA with the complementary anticodon sequence moves to the ribosome and pairs up with the codon on the mRNA. the tRNA carries a specific amino acid
- the ribosome moves along the mRNA bringing together two tRNA molecules at any one time, each pairing up with the corresponding two codons on the mRNA
- the two amino acids on the tRNA are joined by peptide bonds using an enzyme and ATP which is hydrolysed to provide the required
- the ribosome moves onto the 3rd codon, linking the amino acids on. the second and third tRNA molecules
- so the first tRNA molecule is released from its amino acid and is free to collect another one

Question 26

gene mutations def

Answer 26

any change to 1 or more nucleotide bases
or rearrangement of the bases in DNA

Question 27

how can mutations occur

Answer 27

natural - spontaneously during DNA replication (1-2 per 100,000 genes)

mutagens - high energy radiation disrupts DNA molecule, chemicals that alter DNA structure or interfere with transcription

Question 28

3 substitution mutations

Answer 28

non-sense mutation — a stop codon is produced, protein isn’t able to be made

mis-sense mutation — a different αα is produced

silent mutation — the same amino acid produced
(due to degenerate nature of the genetic code)

Question 29

deletion mutation

Answer 29

loss of a single nucleotide - due to the fact DNA is read in triplets, one deleted nucleotide causes all sequential triplets to be read differently as each has been shifted to the left by one base
(frame shift)

Question 30

binary fission in bacteria

Answer 30

circular DNA molecule replicates, both copies attach to cell membrane
plasmids also replicate
cell membrane grows between two DNA molecules and pinches inwards, diving cytoplasm into two
new cell wall forms between two molecules of dna diving original cell into two identical daughter cells, each with a single copy of the circular DNA and a variable number of copies of the plasmids