1- DNA and protein synthesis Flashcards
DNA nucleotide
- deoxyribose
- a phosphate group
- one of the organic bases (adenine, cytosine, guanine, thymine)
RNA nucleotide
- ribose
- a phosphate group
- one of the organic bases (adenine, cytosine, guanine, uracil)
organic base classification
- AG = purines = 2 nitrogen containing rings
- CUT = pyrimidines = 1 nitrogen containing ring (smaller)
nucleotides join together by
phosphodiester bonds in condensation reactions
DNA molecule
a double helix composed of two DNA strands, running anti parallel to each other, that are joined by hydrogen bonds between complementary bases
RNA molecule
a single strand of RNA
hydrogen bonds form between
complementary bases in neighbouring strands
how many bonds for between AT
2 hydrogen bonds
how many bonds form between GC
3 hydrogen bonds
how is DNA replicated?
1) DNA helicase unwinds the double helix by breaking hydrogen bonds between complementary bases
2) free nucleotides form hydrogen bonds with complementary base pairs on the parent strand
3) DNA polymerase forms phosphodiester bonds between adjacent nucleotides in the new strand, through condensation reactions in the 5’ and 3’ direction
4) DNA ligase joins fragments together
codon
a triplet of bases that codes for an amino acid
gene
a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain
structure of tRNA
anticodon
- a sequence of three bases on the tRNA molecule
- complementary to a codon on mRNA
- brings the correct amino acid to the ribosome during protein synthesis
what is transcription
where a molecule of mRNA is made in the nucleus
transcription process
1) RNA polymerase binds to DNA at the promoter region
2) RNA polymerase unwinds a portion of the DNA by breaking its hydrogen bonds
3) RNA polymerase travels along the antisense template strand in a 3’ to 5’ direction. For each nucleotide in the template strand, a matching RNA nucleotide is added to the RNA strand. Free nucleotides form hydrogen bonds with complementary base pairs on the template strand
4) RNA polymerase forms phosphodiester bonds between adjacent nucleotides, resulting in a sugar phosphate backbone
5) RNA polymerase reaches the stop sequence. hydrogen bonds break between the mRNA and DNA, releasing the completed mRNA. RNA detaches from DNA
6) hydrogen bonds reform between the DNA strands, creating the double helix. DNA rewinds
7) mRNA moves out of the nucleus through a nuclear pore in the nuclear envelope
what is translation?
where amino acids join together to form a polypeptide chain
translation process
1) mRNA attaches to a ribosome on the rough endoplasmic reticulum
2) the ribosome slides to the start codon on the mRNA
3) tRNA, which has a specific amino acid attached, binds to mRNA by forming hydrogen bonds between its anticodon and the codon on mRNA
4) peptide bonds form between adjacent amino acids
5) the ribosome reaches the stop codon and detaches. a polypeptide chain is formed
triplet code
three triplets (a codon) code for one amino acid
start and stop codons
the genetic code contains codons that start or stop protein synthesis
degenerate
- more than one triplet codes for the same amino acid
- this reduces the effect of mutations
- mutations may not affect the amino acid, as the new triplet could code for the same one
non- overlapping
each triplet is only read once. triplets don’t share any bases
non- coding regions
- not all of the genome codes for proteins
- the non- coding regions of DNA are called introns
- the coding regions of DNA are called exons
universal
the genetic code is the same in all organisms and species
gene mutations
a change in the nucleotide sequence of base pairs in a section of DNA coding for a specific polypeptide, which may result in an altered polypeptide
types of gene mutations
- base substitution
- base insertion
- base deletion
base substitution
when one base is substituted for another
base insertion
when one base is added
base deletion
when one base is removed
which type of mutation is most likely to be harmful?
an insertion or deletion is more likely to be harmful because it causes a ‘frame shift’ - the entire gene sequence following the mutation will be incorrectly read
what causes sickle cell anemia
point mutations
sickle cell anemia process:
- GAG (glutamic acid) -> GUG (valine)
- the amino acid change causes the haemoglobin to form insoluble fibrous strands
- it can’t carry oxygen as effectively, as it is insoluble, causing fatigue
- it changes shape of the red blood cell, causing them to be stiff and sickle shaped. these red blood cells tend to get stuck in narrow blood vessels and cause reduced blood flow or clots
- this leads to strokes, blindness or joint pain
DNA nucleotide
- deoxyribose
- a phosphate group
- one organic base (adenine, cytosine, guanine, thymine)
RNA nucleotide
- ribose
- a phosphate group
- one organic base (adenine, cytosine, guanine or uracil)
organic base classification:
- AG = purines = 2 nitrogen containing rings
- CUT = pyrimidines =
