Nucleic Acids Flashcards
Why is ATP a better source of energy than glucose? (2)
- energy released rapidly from a single reaction
- energy released in manageable quantities
Why so much ATP synthesised every day? (3)
- ATP is unstable
- ATP is immediate source of energy / cant be stored
- ATP only releases small amount of energy at a time
what are homologous chromosomes?
- pair of chromosomes
- with same genes
Explain how structure of DNA is related to its function: (6)
- Sugar-phosphate (backbone) so provides strength
- large molecule so can store lots of information
- coiled so compact
- base sequence codes for amino acids
- double stranded so replication can occur semi-conservatively
- (Weak) hydrogen bonds for replication / unzipping
what is degenerate
more than one (base) triplet for each amino acid
what is non-overlapping
each base is part of only one triplet
why can nucleotides only be added in a 5’ to 3’ direction
- DNA polymerase
- is specific
- only complimentary to 5’ end
- shapes of 5’ end and 3’ end are different
desc. role of DNA polymerase in DNA rep.
joins nucleotides together by forming phospho. bonds
Describe semi con. replication
- DNA helicase -> H-bonds betw/ bases to break, polynucleotide chains to separate
- Both strands act as templates
- Free DNA nucleotides attach to e/ strand by comp. base pairing
- H-bonds form betw comp/ base pairs
- DNA polymerase forms phosphodiester bonds betw/ adj. nucleotides on new strand -> cond. reaction
- Two new DNA molecules made. e/ consist of one new & old strand -> semi con. rep
Features of DNA important in semi-con replication (3)
- H-bonds betw/ base pairs
weak -> easily broken, allows strands to separate - two strands
both can act template - comp base pairings
allows accurate replication of gen. info
meaning of degenerate
more than one triplet for e/ amino acid
meaning of non-overlapping
each base is part of only one triplet
pentose sugar name in DNA & RNA
DNA: deoxyribose
RNA: ribose
what is a homologous chromosome
- one maternal and one paternal
- carry same genes
- pair up in meiosis
4 features of ATP that make it useful in bio molecules:
- releases energy in small amounts
- releases energy in just one step by breaking covalent phosphate bond; energy rapidly available
- can phosphorylate other molecules to make them more reactive
- can be regenerated
2: equations for ATP
ATP + water —- (ATP hydrolase) processes in the cell which require energy –> ATD +Pi + energy
ATD +Pi + energy — (ATP synthase) resp/ photosynthesis –> ATP + water
compare and contrast prokaryotic and eukaryotic DNA (5)
COMPARISONS
1. nucleotide structure identical
2. nucleotides joined by phosphodiester bonds
3. DNA in mito and chloro have similar structure to prokaryotic
CONTRASTS
1. eukaryotic DNA longer
2. eukaryotic DNA has introns, prokaryotic doesn’t
3. eukaryotic DNA is linear, prokaryotic is circular
4. eukaryotic DNA associated w/ histones, prokaryotic DNA is not
Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus. [3 marks]
- chloro DNA is circular, nuclear DNA is linear
- nucleus DNA longer than chloro DNA
- chloro DNA not associated w/ histones, nuclear DNA is
- chloro DNA doesn’t have introns, nuclear DNA does
Describe the DNA of MITOCHONDRIA and CHLOROPLASTS in eukaryotic cells. (same for prokaryotic DNA)
- small
- circular
- not associated w/ proteins
what is meant by universal
same triplet of bases codes for the same amino acid in all organisms
desc. how competitive and non-competitive inhibitors can limit enzyme activity (6)
COMPETITIVE
* inhibitor similar in shape to substrate
* inhibitor complimentary in shape to active site
* binds to active site and prevents substrate from binding
* fewer ES complexes formed
NON-COMPETITIVE
* inhibitor comp. to an allosteric site on enzyme; binds to allosteric site
* changes tertiary structure of active site; shape changes
* active site no longer comp. to substrate
* fewer ES complexes formed
explain why ATP is useful in biological processes (4)
- phosphorylates substances to make them more reactive
- broken down in one step; energy rapidly available
- reformed/ made again
- releases energy in small, manageable amounts
Explain how a change in the DNA base sequence for a protein may result in a change in the structure of the protein. [3 marks]
- change in amino acids/primary structure
- changes position of hydrogen bonds, ionic bonds and disulfide bridges
- alters tertiary structure
Describe how substances can cross a cell surface membrane. (5)
- (Simple / facilitated) diffusion down concentration gradient;
- Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer;
- Water moves by osmosis / from high water potential to low water potential
- Active transport is movement against concentration gradient;
- Active transport / facilitated diffusion involves proteins/carriers;
- Active transport requires energy / ATP;
give 4 ways in which pro is different to eu DNA
- prokaryotic: circular but eukaryotic linear
- prokaryotic not associated w/ proteins
- prokaryotic is smaller
- prokaryotic has no introns
DNA strand, polymerase
Why do the arrows point in different directions? (4)
- DNA Has anti parallel strands
- Shape of nucleotide is different
- enzymes have active sites w specific shapes
- Only substrates with complementary shape can bind with active sight of Enzyme
what are phosphates useful for
- to make DNA / RNA
- for phosphorylation
- to make ATP
- to make membranes
What is the role of single stranded DNA fragments in semiconservative replication
To act as a template and determine order of nucleotides
What is the role of DNA nucleotides in semi conservative replication
Forms complementary base pairings
tRNA
- only found in cytoplasm
- clover leaf shaped, held in place by H-bonds
- tRNA attatches to an amino and transfers it to the ribosome to create polypep chain
- specific tRNA molecules attatch to specific amino acids, determined by 3 bases found on tRNA complementary to 3 bases on mRNA
- called anticodon
