2B & C Proteins, Genetics and Inheritance Flashcards
gene
seq. of bases on DNA molecule that code for a seq of a.a in a polypeptide chain
allele
different form of a gene -> diff alleles = diff base seq.
found at same locus on chromosome
genotype
alleles a person has eg. Bb/BB/bb
phenotype
characteristic of organism eg. brown eyes
dominant allele
allele that produces a characteristic when
1+ copy is present eg. BB
recessive allele
allele that produces characteristic when
2 copies present eg. bb
incomplete dominance
when dominant allele trait isn’t completely shown over recessive allele trait
-> both alleles expressed
eg. RR -> red flowers rr -> white flowers
Rr -> PINK FLOWERS
homozygote
organism that has 2 identical alleles of particular gene -> eg. BB/bb
heterozygote
organism that has 2 different alleles of particular gene -> eg. Bb
carrier
organism that has 1 dominant, 1 recessive (hetero.) so DOESN’T have disease but carries copy of allele for disease
mutation
changes to base seq of DNA
caused by errors in DNA replication
what errors in DNA replication cause mutations?
- SUBSTITUTION -> change in 1 base
- DELETION -> deleting 1 base
- INSERTION -> adding 1 base
- DUPLICATION -> adding same base more than once
- INVERSION -> seq of bases REVERSED
ID IDs
Order of DNA bases determines order of a.a in protein.
What happens if mutation is present?
- primary structure changed
- could change 3D shape of protein
- so doesn’t work properly
what happens if there is a mutation in gene?
can cause genetic disorder eg. CF
how is CF obtained?
caused by mutation in gene coding for
CTFR protein
what is a CTFR protein?
- channel protein
- moves Cl⁻ ions from cells -> mucus
-> causes H₂O to move into mucus by osmosis
= watery mucus
how does mutant CTFR affect its function?
less efficient at transporting Cl⁻ ions OUT of cell
= less water moves out by osmosis = THICK MUCUS
how does CF affect respiratory system?
- buildup mucus in lungs traps bacteria = higher risk of infection
- buildup mucus in airways -> caused by cilia unable to move mucus
-> some airways blocked = gas exchange decreases
= less s.a for gas exchange = DIFFICULTY BREATHING
how does CF affect digestive system?
- tube that goes from pancreas->small intestine can get blocked by mucus
-> prevents dig. enzymes reaching small intestine = less able to digest food so LESS NUTRIENTS ABSORBED - mucus can cause CYSTS IN PANCREAS = stops production of enzymes …
- mucus lining small intestine is v thick = STOPS ABSORPTION OF NUTRIENTS
how does CF affect reproductive system?
mucus supposed to prevent infection and move sex cells
MEN: vas deferens (tube connecting balls to dick) is absent / blocked by mucus = SPERM NEVER REACHES DICK
WOMEN: thick cervical mucus prevents sperm reaching egg -> decreases mobility of sperm = DECREASES CHANCE OF MAKING IT TO EGG
what are the main uses of genetic screening?
- identifying people carrying allele at locus for particular disorder
- screening embryos BEFORE IMPLANTATION in fertility treatment (PGD)
- testing foetus before birth -> PRENATAL TESTING
what are there roles of tRNA?
- carries a.a to ribosomes (in translation)
- each tRNA carries a SPECIFIC A.A
- tRNAs ANTICODON BIND TO mRNAs CODON
role of mRNA?
carries genetic code from DNA in nucleus -> cytoplasm where its used to make a PROTEIN during translation
3 differences between replication of DNA and transcription of DNA
- replication inv. DNA NUCLEOTIDES whereas transcription inv. RNA NUCLEOTIDES
- replication: makes double stranded DNA whereas
transcription: makes single stranded RNA - replication: makes IDENTICAL COPIES whereas
transcription: makes COMPLIMENTARY COPIES
semi conservative DNA replication
1/2 strands in new DNA mol. are from o.g
therefore GENETIC CONTINUITY between generations of cells
describe the process of DNA replication
- DNAhelicase (enzyme) breaks H-bonds between bases on 2 POLYNUCLEOTIDE DNA STRANDS -> makes helix unravel
- o.g strand acts as TEMPLATE for new one -> COMPLIMENTARY BASE PAIRING = free DNA nucleotides ATTRACTED to EXPOSED BASES
-
CONDENSATION REACTIONS join nucleotides together (catalysed by DNApolymerase)
-> H-bonds form between o.g bases and new
describe the structure of DNA
- complimentary base pairing and H-bonding between 2 polynucleotide strands
- strands are antiparallel
- phosphodiester bonds between deoxyribose and phosphate (a.k.a backbone)
where does translation occur?
cytoplasm
describe translation in protein synthesis
- mRNA molecule attaches to a ribosome
- in cytoplasm: free molecules of tRNA
- tRNA binds to specific a.a (also in cytoplasm) and bring them to mRNA on ribosome
- ANTICODON on each tRNA pairs with COMPLEMENTARY TRIPLET on the mRNA = CODON (inc start codon on mRNA)
- 2 tRNA fit onto ribosome at one time -> bring a.a they are each carrying side by side
- PEPTIDE BOND formed, via a CONDENSATION REACTION, BETWEEN the 2 a.a
- process continues until STOP CODON on the mRNA reached
- a.a is complete -> forms FINAL POLYPEPTIDE
describe the structure of tRNA
- triplet of unpaired bases at one end = anticodon
- region at the other end where a specific a.a can attach
what is a START CODON?
- Near beginning of the mRNA is a triplet of bases called the start codon (AUG)
- This is a signal to START OFF TRANSLATION
- AUG codes for a.a METHIONINE
how does a mutation prevent enzyme functioning properly?
- if folded incorrectly -> substrate doesn’t fit in active site
- mutation leads to CHANGES IN SEQ OF BASES
- … leads to DIFF A.A
- changes 3° STRUCTURE
non-overlapping genetic code
each 3 a.a are DISTINCT -> base is only used once in triplet
adv. of a.a having more than one code
-
effect of mutations reduced
-> a.a may not be altered - no affect on protein
how are a.a joined together in a polypeptide
- PEPTIDE BOND -> between amine and carb. acid group in CONDENSATION reaction
dipeptide
2 a.a bonded together
polypeptide
chain of 2+ a.a bonded together
degenerate code
a.a can be coded for by more than one codon
triplet code
3 bases (1 codon) code for 1 a.a
genetic code
seq of base triplets (codons) in DNA or mRNA which codes for specific a.a
- non-overlapping
- degenerate
what does gene therapy involve?
using various mechanisms to alter person’s genetic material to treat / cure diseases
what are 4 factors that affect enzyme activity?
- temp
- enzyme conc
- substrate conc
- pH
how is initial rate of reaction calculated over time?
(enzyme practical)
1 / time
what is effect of enzyme conc on enzyme activity?
(enzyme practical)
as enzyme conc increases = increased no. enzyme-substrate complexes made
-> as more frequent successful collisions between SUBSTRATE and ACTIVE SITE form enzyme-substrate complexes
-> so rate increases to an optimum
describe the 2 types of test for screening fetuses for genetic disorders
prenatal testing
- AMNIOCENTESIS
-> testing sample cells from amniotic fluid (contains fetal cells which has DNA)
-> sample obtained using v fine needle into abdomen
-> small risk miscarriage
- CHORIONIC VILLI SAMPLING (CVS)
-> testing sample cells from chorionic villi (part of fetus connecting to mother) containing fetal DNA
-> using v fine needle into abdomen OR vagina with catheter
-> small risk miscarriage
discuss the social / ethical viewpoints related to genetic screening
identification of carriers
PROS
-> allows ppl to make informed decision before having children
CONS
-> emotional distress
-> tests aren’t 100% accurate = decisions made on false info
-> genetic discrimination
PGD
PROS
->** less chance** baby having genetic disorder
-> as before implantation = avoids abortion issues
CONS
-> used to find out other characteristics
= leads to designer babies
explain why the secondary structure of a protein is an ɑ helix or a β pleated sheet
H-bonds form between a.a in polypeptide chain
-> makes it coil (ɑ helix) or fold (β pleated sheet)
what determines the tertiary structure of a protein?
(4 marks)
- ionic bonds
- disulphide bonds
-> when 2 molecules of a.a cysteine get close: sulphur atom bonds to other sulphur in other cysteine -> forming disulphide bond - hydrophobic/philic interactions -> hydrophobic groups clump together when close
-> so hydrophilic grouos more likely to be pushed to outside
-> affects how protein folds up in final structure - H-bonds
explain how a protein’s primary structure determines its 3D structure and properties
(3 marks)
- a.a seq of protein determines what bonds will form and how protein will fold up into 3D structure
- eg. if many cysteines -> form disulphide bonds (keratin)
with each other and protein folds in certain way - 3D structure (globular / fibrous) determines properties which relate to its function in body
describe the globular 3D structure of proteins
eg. haemoglobin
- spherical made of multiple polypeptide chains
- chains are coiled up so hydrophilic parts on outside of molecule and hydrophobic parts of chain face inwards
-> making molecules soluble so easily transported in fluids
haemoglobin is a globular protein. explain how this is useful for its function
- made of 4 polypeptide chains
- carries O₂ around body in blood
- chains coiled up so hydrophilic parts on outside and hydrophobic parts of chain face inwards …
- … making them soluble so easily transported in blood
- has cooperative binding so changes shape when it binds to O₂
-> makes it easier for next one to bind - has iron containing 4 haem groups that bind to O₂
collagen is a fibrous protein. explain how this is useful to its function
(4 marks)
- long insoluble (doesn’t affect water potential of cells as it holds body cells together)
- primary structure twisted into ɑ helix
- 3 helixes twist to form triple superhelix (also held together by H-bonds)
- chains held together by lots of H-bonds
-> makes protein strong - collagen is strong and stable but flexible so good for forming connective tissue
describe the fibrous 3D structure of proteins
eg. collagen, keratin
- long, insoluble polypeptide chains that are tightly coiled to form rope shape
- chains held together by lots of bonds (disulphide, H-bonds)
-> makes protein strong
-> so found in supportive tissue
describe what might happen to polypeptide to make it a functional enzyme
is this right??
- folded to make globular shape which is precise for function as an enzyme
- 3D shape held together by bonds between R groups (eg. ionic, disulphide) to produce active site
intracellular enzymes
catalyse reactions inside cells
extracellular enzymes
- produced and secreted by cells
- to catalyse reactions outside cells
what is an enzyme?
(2 marks)
- proteins that speed up chemical reactions …
- by acting as biological catalysts that reduce Ea
explain how enzyme properties relate to their tertiary structure
(5 marks)
- enzymes are v specific -> usually only catalyse 1 reaction (eg. maltase only breaks down maltose)
- as only 1 complementary substrate will fit into active site
- active site shape determined by enzymes tertiary structure
- tertiary structure determined by primary structure
- so each enzyme has diff tertiary = diff primary structure = diff active site shape
- if substrate shape doesn’t match active site = enzyme-substrate complex not formed = reaction not catalysed
what happens if the tertiary structure of an enzyme is altered?
(3 marks)
- shape of active site changes …
- so substrate won’t fit into active site …
- so enzyme-substrate complex not formed …
- so enzyme cannot carry out its function :(
what causes a change in tertiary structure?
- changes in pH / temp
- primary structure determined by gene
- if mutation occurs in gene -> could change tertiary structure of enzyme produced
(polyploidy)
occurs when an organism has more than two sets of homologous chromosomes
caused by mutation
design an experiment to investigate the effect of enzyme and substrate conc on initial rate of reaction
control variables
-> temp
-> vol enzyme sol - 2cm³ trypsin
-> vol substrate - 5cm³ casein
-> conc substrate
METHOD
- set up water bath so temp kept constant
- mark X on one side of test tube -> fill with 5cm³ casein sol and place in water bath with 2nd test tube with 2cm³ trypsin (start at lowest conc 0.2%)
- allow subs to acclimatise for 3 mins so both at same temp
- add test tube trypsin to casein and start stopwatch -> time how long until casein sol turns transparent (when you clearly see X mark)
- repeat 2x more then repeat with other conc (0.0%, 0.4%, 0.6%, 0.8%, 1.0%)
initial rate of reaction 𝛼 enzyme conc
as ↑ enzymes present = ↑ active sites available to form enzyme-sub complexes
Meselson and Stahl provided evidence that DNA replication is semi-conservative.
describe how they proved this
(6 marks)
- 2 samples bacteria grown -> 1 in nutrient broth containing light, other heavy
-> as bacteria reproduced, took up N from broth to make nucelotides for new DNA -> so N became part of bacterial DNA - DNA contains Nitrogen -> so used two isotopes … ¹⁵N (heavy) and ¹⁴N (light)
- light DNA settled at top of centrifuge, heavy settled near bottom
- heavy N bacteria replicated in light N broth
- if DNA conservative, heavy DNA would still be together and sit at bottom and new light N would settle at top
- BUT semi-conservative DNA, new bacterial DNA would contain 1 light, 1 heavy strand …
- … and DNA would settle between where light N DNA and heavy N DNA settled
describe transcription in protein synthesis
- RNA polymerase (enzyme) attaches to DNA double helix at start codon
- H-bonds broken between strands and helix unravels
- one strand used as template to make mRNA copy
- RNA polymerase lines up RNA mononucleotides along template strand
- complementary base pairing means mRNA strand is complimentary copy of DNA template (antisense) strand -> bases joined by RNA polymerase, forming mRNA molecule
- RNA polymerase moves along DNA, separating strand and making mRNA strand
- H-bonds between DNA strands reform once RNA polymerase has passed by - reforms double helix
- when RNA polymerase reaches stop codon -> stops making mRNA and detaches from DNA
- mRNA moves from nucleus->cytoplasm through nuclear pore
