story of us part 2 3.18B, 3.35B, 3.38, 3.39

Question 1

what is protein synthesis?

Answer 1

dna remains in the nucleus but a copy called mRNA moves from the nucleus to the ribosomes where proteins are synthesised in the cytoplasm

the protein produced depends on the sequence of bases in mRNA

tRNA bring specific amino acids to add to the growing protein in the correct order

the protein molecule has thousands of amino acids joined together and then it is folder into the correct unique shape - important as it allows the protein to do its job

Question 2

short explanation of protein synthesis:

Answer 2

cells express their genes by converting the genetic message into protein, this process of protein synthesis occurs in two stages - transcription and translation

Question 3

what is transcription?

Answer 3

when a gene is to be expressed this sequence of bases in dna is copied or transcribed into mRNA, this process takes place in the nucleus and occurs in a series of stages:
1. two strands of DNA helix are unzipped by breaking the weak hydrogen bonds between base pairs, this unwinding of the helix is caused by an enzyme (helicase)
2. enzyme rna polymerase attaches to the dna just before the gene
3. rna polymerase moves along the dna strand, free rna nucleotides are attracted to (forming hydrogen bonds) the exposed dna strand nucleotides by complementary base pairing
4. RNA polymerase then catalyses the formation of covalent bonds between the RNA nucleotides to form a strand of mRNA
5. newly formed strand of mRNA is now ready to leave the nucleus and travel to the ribosomes

Question 4

what is natural selection?

Answer 4

‘survival of the fittest’
charles darwin came up with it

Question 5

observations made about natural selection:

Answer 5

• species show variation in their characteristics
• resources that organisms need to survive are limited and individuals have to compete for these resources to survive
• organisms with the most suitable characteristics for the environment would be more successful competitors and would have a better chance of survival
• successful organisms will have an increased chance of breeding and passing on their genes
• a greater proportion of individuals in the next generation will have better alleles so characteristics that help survival
• the characteristics that increase survival become more common, making the species survive more

Question 6

antibiotic resistance relating to natural selection:

Answer 6

1. random mutation causing new alleles for antibiotic resistance
2. selection pressure - exposure to antibiotic resistance causes mutated alleles/organisms to be at an advantage
3. mutated alleles/organisms survive and reproduce
4. mutated alleles passed on to next generations
5. allele increased in population
6. over time creates a new species or population

Question 7

what is DNA and codons needed to make?

Answer 7

DNA contains the information needed to make a protein, the three bases (codon) code for a specific amino acid
= so the bases are a set of instructions for which order to join amino acids in to make a protein

Question 8

what is translation?

Answer 8

1. the mRNA strand travels through the cytoplasm and attaches to the ribosome, the strand passes through the ribosome
2. for every 3 mRNA bases the ribosome lines up one complementary molecule of tRNA, we call every three bases on mRNA a codon, the complementary three bases on the tRNA are an anticodon
3. tRNA molecules transport specific amino acids to the ribosome, the ribosome allows two tRNA molecules to sit next to each other, the ribosome catalyses the information of a covalent bond (peptide bond) between the two amino acids
4. used tRNA molecules exit the ribosome and collect another specific amino acid
5. a chain of several hundred amino acids forms in the correct order according to the original DNA is then made, this is called a polypeptide

Question 9

what happens after translation?

Answer 9

the polypeptide is folded into the correct shape and becomes a protein