2.1.3 nucleotides and nucleic acids Flashcards
2 nucleic acids
RNA, DNA
Nucleic acid monomer
nucleotide
3 components of a nucleotide
- phosphate group
- pentose sugar
- nitrogenous base
purine
- 2 rings
- adenine and Guanine
pyrimidine
- 1 ring
-2 cytosine, thymine and uracil
Differences in RNA and DNA
RNA IS
- non helical
- single stranded
- shorter than DNA
- ribose sugar
- URACIL instead of thymine
why is RNA shorter than DNA
only contains the small portion of the genetic code necessary for its function
3 types of RNA
- mRNA (carries gene out of nucleus and to ribosomes)
- tRNA (transports amino acids to ribosomes)
- rRNA (makes up the ribosome)
structure of DNA
- 2 polynucleotide strands of nucleotide monomers
- lie in opposite antiparallel directions
- double helix
- 2 strands held together by CBP - (purine to pyrimidine)
H bonds between A and T (or U)
2
H bonds between C and G
3
gene
sequence of DNA nucleotides that code for a protein
why cant DNA itself leave the nucleus
- too big to fit through the small pores in the nuclear envelope
evidence for CBP
- similar amounts of A and T , then C and G
HOW ARE PHOSPHODIESTER BONDS FORMED
condensation
bonds between nucleotides
phosphodiester
how to break a phosphodiester bond
hydrolysis
ADP and ATP are …
phosphorylated nucleotides
structure of ADP and ATP
- pentose sugar (ribose)
- nitrogenous base (adenine)
- 2 or 3 inorganic phosphates
STEPS OF DNA REPLICATION (7)
- double stranded molecule untwists and molecule UNZIPS (H bonds between complementary bases break) catalysed by DNA helicase
- 2 chains separate, exposing the bases, creating a Y shaped replication fork. each strand is used as a template to make 2 new double strands
- LEADING STRAND oriented in the 3’ to 5’ direction (towards the fork). LAGGING STRAND oriented in the 5’ to 3’ way (AWAY FROM THE FORK)
- Free phosphorylated nucleotides from nucleoplasm bond to bases by CBP
- LEADING STRAND : DNA polymerase catalyses addition of the CPBs in the 5’ to 3’ direction. forms the phosphodiester bonds CONTINUOUS
- LAGGING STRAND: DNA chunks (Okazaki fragments) are added to the lagging strand also in the 5’ to 3’ direction. DISCONTINOUS as need to be joined up later by ligase
- DNA proofread.
- twists to form double helix
how does the structure of DNA allow replication
- double stranded helix (2 antiparallel strands)
- BOTH act as a template
- weak H bonds between complementary base pairs easy to break
- purins ONLY bind to pyrimidines due to their different sizes
- 2 bonds A-T. 3 bonds C-G
mutatin in DNA leads to different tertiary structure
- change in base sequence (different primary structure)
- R groups interact differently (ionic bonds, h bonds etc)
- THIS DETERMINES tertiary structure, which is 3D shape
describe how the polypeptide chains are held together
- phosphodiester bonds between sugar and phosphate group forms sugar phosphate backbone
- H bonds between bases
- 2 H bonds A-T, 3 between C-G
- purine only to pyrimidine as different sizes
how is the sugar phosphate backbone formed
- DNA polymerase
- condensation between phosphate and sugar of adjacent nucleotides
how is dna organised in eukaryotes?
- nucleus
- each large DNA molecules wound around HISTONE proteins. 1 chromosome = 1 molecule of DNA
where does the energy to make phosphodiester bonds come from
- hydrolysis of activated nucleotides
- to release the extra phosphate groups
how to extract DNA
- macerate tissue using a pestle and mortar
- add detergent
- att ethanol so DNA precipitates out
gene
short section of DNA that codes for a protein
4 examples of where tertiary structure is important for protien
- enzyme active site complementary to substrate
- variable region of antibody complementary to antigen
- receptor on cell membrane shape complementary to cell signalling molecule
- ion channel protein has HPO AA on the inside and LIPOPHILIC aa on the outside
nature of genetic code (3)
- near UNIVERSAL (same triplet of bases codes for same AA)
- DEGENERATE (more than one base triplet for each AA) reduces harm of mutation
- NON-OVERLAPPING
transcription steps (5)
- gene unwinds and unzips
- H bonds between cbp break
- RNA POLYMERASE catalyses the temporary formation of H bonds between RNA nucleotides and the complementary bases, on the TEMPLATE STRAND
- free nucleotides use CBP to produce the coding strand (comp to the template RNA strand)
- mRNA passes out of nucleus, through nuclear envelope to a ribosome
how are ribosomes made
- in nucleolus in 2 smaller subunits
- pass separately out of nuclear envelope pores and then bind together helped by MAGNESIUM IONS
2 susbunits of ribsosome
- ribosomal RNA
- protein
Translation
- tRNA brings amino acids, anticodon temperarily H bonds to complementary codon on mRNA
- ribosome moves along the mRNA, synthesising a peptide bond between
- ENERGY NEEDED
- PPC assembled, folds into tertiary 3d structure
- mRNA breaks down and molecules can be recycledf into new mRNA
tRNA
- made in nucleolus
- single strand PPC
- at one end is a trio of bases that recognises and attaches to a specific amino acis.
- also has another triplet of bases (ANTICODON) complementary to a specific codon of bases on the mRNA
methyl green pyronin stain
DNA = green
RNA = red
why ight there be a triplet which doesnt have an amino acid
STOP CODON: protein finished
purpose of crushing tissue before extracting DNA
break cell walls
purpose of using detergent in experiment
break down PHOSPHOLIPID BILAYAER
enzyme that should be used in DNA experiment
-protease
-break down histones
whats it called when the white layer of DNA forms?
precipitation
why no need to crush animal cells
no cell wall
purpose of adding salt and ethanol in DNA experiment
- precipitate out the DNA from the aqueous solution
similarities DNA and ATP (4)
- pentose sugar
- adenine base
- phosphodiester bond
- contain phosphate
differences DNA and ATP (2)
- ATP has 2 additional phosphates
- ATP has ribose sugar instead of deoxyribose
differences DNA and ADP (2)
- ADP has ribose whereas DNA has deoxyribose
- ADP has 2 phosphates whereas DNA has 1 phosphate
why is only a small proportion of your mass ATP at the end of the day despite loads being made?
- ATP Broken down
- used to provide energy for metabolic reactions
similarities DNA replication and transcription (7)
- DNA unwinds and unzips
- helicase to unzip
- template DNA
- CBP
- hydrogen bonds
- free activated nucleotides
- polymerase enzymes
differences DNA replication and transcription
- only a small section of DNA unzipped in transcirption
- BOTH strands are templates in replication
- RNA vs DNA free nucleotides
- RNA vs DNA polymerase
- one strand produced in RNA, 2 in DNA
- mRNA leaves nucleus, but DNA strand remains bound to the template strand
why are enzymes essential to all organisms (2)
- catalysts: speed up reactions by lowering activation energy, allowing reactions to take place at lower body temperatures
- the hgih temperatures needed otherwise would denature proteins
why is replication semi-conservative?
- contains one old strand and one new strand
- EACH dna strand acts as a template strand
importance of TRANSCRIPTION
- translation must take place at ribosome
- DNA transcribed to mRNA
- as DNA is too large to leave through the small pores in the nuclear envelope
