Topic 2 : Genes and Health Flashcards
why do organisms with low SA:V ratio need specialised gas exchange surfaces
bc diffusion alone is not sufficient
3 features of an efficient gas exchange surface
1) large surface area
2) thin/short distance
3) steep concentration gradient
what is Ficks law? Give the corresponding equation.
increased SA and greater conc grad increase the rate of diffusion.
thicker diffusion distances reduce the rate of diffusion
diffusion distance
how are mammal lungs adapted for gas exchange?
- Alveoli provide a large SA
- Good blood supply = maintains steep conc grad
- one cell thick = short diffusion distance
structure of cell membrane
- phospholipid bilayer
- channel proteins
- carrier proteins
- glycoproteins
- glycolipids
- cholesterol
why is it called a fluid mosaic model?
Cell membranes are fluid and have a mosaic like arrangement
what evidence led to development of fluid mosaic model?
- microscopes show proteins on membrane surface
- lipid soluble substances pass more easily in and out of cells than water soluble
define osmosis
the net movement of free water molecules from an area of high conc to an area of low conc across a partially permeable membrane
what is passive transport
movement of particles down a conc grad, no energy required
diffusion, facilitated diffusion and osmosis
define diffusion
net movement of small, non-polar, lipid-soluble molecules from an area of high conc to an area of low conc.
define facilitated diffusion
movement of polar, charged, water-soluble particles from high to low conc through a carrier protein or channel protein
define active transport
movement of molecules against a conc grad
energy in the form of ATP is required. Also uses carrier proteins.
what is the process of endocytosis
cell membrane forms a vesicle and engulfs the substance, which enters the cytoplasm
what is endocytosis used for
to bring large molecules into the cell
eg proteins
lipids
some carbohydrates
what is the process of exocytosis
vesicle forms from the Golgi apparatus and moves towards the cell membrane. Vesicle fuses with cell membrane to release contents from cell
what is exocytosis used for
to secrete substances produced by the cell eg hormones, some enzymes, and lipids
how are nucleotides formed
via a condensation reaction forming phosphodiester bonds
what is DNA made up of?
phosphate, deoxyribose sugar, and a nitrogenous base : adenine, thymine, guanine and cytosine.
What is RNA made up of?
phosphate, ribose sugar, and a nitrogenous base : adenine, uracil, guanine and cytosine
what are the 2 structural forms of a nitrogenous base?
purine or pyrimidines
what are purines… and what bases are purines
what are pyrimidines… and what bases are pyrimidines
purines = double ring structure
eg adenine and guanine
pyrimidines = single ring structure
eg cytosine, thymine and uracil
how are the antiparallel dna strands bonded
the complimentary bases are hydrogen bonded together
properties of RNA
single stranded
uracil base instead of thymine
ribose sugar
relatively short
different types of RNA
tRNA
mRNA
rRNA
What is a gene?
a sequence of nucleotide bases in dna that codes for the production of specific amino acids
what is transcription?
when dna is transcribed and an mRNA molecule is produced
what is translation
mRNA is translated to the cytoplasm and an amino acid sequence is produced
what happens during transcription
DNA helicase unzips and the hydrogen bonds between the bases break
free activated RNA nucleotides pair up with their base pairs on the antisense strand …. making the RNA strand
catalysed by RNA polymerase
where does transcription occur
nucleus
where does translation occur
cytoplasm
what happens during translation
mRNA leaves the nucleus and attaches to a ribosome
tRNA molecules bind with their specific amino acids in the cytoplasm and bring them ribosome
tRNA anticodon pairs with the codon on the mRNA
amino acids attached to the tRNA form peptide bonds and primary structure.
Translation is caused by a start and a stop codon.
The code is non overlapping and degenerate.
what does a non overlapping and degenerate code mean?
non overlapping = each codon codes only for a particular amino acid i.e each code is only read once
degenerate = an amino acid can be produced from different triplets of bases.
how many amino acids are there?
20
what is the general structure of an amino acid?
draw it
amine group = NH2
Carboxyl group = COOH
Hydrogen and R group
H H O
N - C - C
H R OH
what is the name of the bond that forms between amino acids?
peptide bonds
what atoms are lost from the amino acids to form a peptide bond
OH of one COOH group
H from the amine group of another amino acid
in what reaction are peptide bonds formed, what are the products
condensation reaction… 1 water molecule
in what reaction are peptide bonds broken?
hydrolysis, add one molecule of water
what is the primary structure of a protein
sequence of amino acids bonded together by peptide bonds
what is the secondary structure of a protein
chain coils into an alpha helix
H bonds form between every 4th peptide bond
or
folds into a beta pleated sheet
two parts of the pp chain are parallel + form H bonds w each other
what is the tertiary structure of a protein
additional bonds forming between R groups
what bonds form and where in a tertiary structure
H bonds between R groups
Disulphide bonds between cysteine amino acids
Ionic between charged R groups
Hydrophobic and Hydrophilic interactions between non polar R groups
what is a quaternary structure
when more than one polypeptide chain is involved
describe globular and fibrous proteins… give examples of each one
globular = compact, spherical, soluble. HAEMOGLOBIN
GCSS - garry can suck sally
fibrous = long crosslinked chains, insoluble, little to no tertiary structure COLLAGEN
why do globular proteins form a spherical shape in their tertiary structure
non polar hydrophobic R groups are towards the centre of the protein
polar hydrophilic R groups are towards the outside
why are globular proteins soluble…what does this allow them to do ?
soluble b/c orientation of the R groups… water molecules can surround the polar hydrophilic R groups
solubility means they can be easily transported around organisms and involved in metabolic reactions
what is the structure of haemoglobin?
quaternary structure… 4 polypeptide chains… 2 alpha globin and 2 beta globins each with a prosthetic haem group
the four globin chains are held together by disulphide bonds
each haemoglobin can carry 4 oxygen molecules b/c each haem group contains Fe2+
properties of haemoglobin
- binds to O2 in the lungs and transports to tissues for aerobic respiration
O2 not very soluble so HG allows it to be carried more efficiently around the body
existence of Fe2+ in the haem group allows for O2 to bind reversibly. Amino Acids unable to bind to oxygen
properties of fibrous proteins
- insoluble and strong
suitable for structural roles - rarely ever tertiary structures
what is collagen
a fibrous structural protein
forms:
tendons, cartilage, ligaments, bones, teeth, skin, cornea
structure of collagen
3 polypeptide chains held together by hydrogen bonds to form a triple helix
covalent bonds form cross-links between R groups
collagen molecules are positioned in the fibrils… many fibrils form fibres = collagen fibres
function of collagen
forms protective tissues
many H bonds = great tensile strength
staggered ends within collagen molecules in the fibrils = strength
collagen = stable b/c the many proline and hydroxyproline repel eachother
what is the role of enzymes
biological catalysts, speed up rate of reactions by reducing activation energy
can be intracellular or extracellular
structure of enzymes
globular proteins with complex tertiary structures
sometimes quaternary
what are intracellular and extracellular enzymes
intracellular = produced and function inside of the cell
extracellular = secreted by the cell and function outside
what conditions cause an enzyme to denature
extreme temp / pH
what conditions are needed for an enzyme-substrate complex to form
substrates must collide with active site at the correct orientation and speed
what does the induced-fit hypothesis state about how enzymes work?
enzyme and substrate interact w each other
- enzyme + active site can change shape slightly as substrate enters the enzyme
- these changes AKA conformational changes
they ensure ideal binding arrangement and maximises the ability of the enzyme to catalyse
what is the name of the process in which DNA is replicated?
semi conservative replication
why is DNA replication process called “semi conservative”
in each new DNA molecule, one strand has conserved the original DNA and then used this to create a new strand
why is it important to retain one original DNA strand
it ensures there is genetic continuity between generations of cells
important as cells are replaced regularly … we need the new cells to carry out the same roles as the old ones
when does DNA replication occur
in preparation for mitosis in the S phase of the cell cycle
what is the process of semi-conservative replication?
enzyme helicase unwinds the double helix by breaking the hydrogen bonds between the base pairs.
each single polynucleotide strand acts as a template for the formation of a new strand made from free nucleotides that are attracted to the exposed dna bases
the new nucleotides are then joined together.
The OG strand and new strand join together via H bonding between base pairs.
what enzyme is involved in joining the new nucleotides together
dna polymerase
what are the free nucleotides that contain 3 phosphate groups called?
nucleotide triphosphates or activated phosphates
what does DNA polymerase do?
catalyses condensation reactions between the deoxyribose sugar and the phosphate groups - creating the sugar-phosphate backbone
cleaves the two extra phosphate groups on the triphosphates and uses the energy released to create phosphodiester bonds
hydrogen bonds then form between the complimentary base pairs of the template and new DNA strand
what direction does dna polymerase build the new strand
5’ to 3’ direction
what is the leading strand?
what is the lagging strand?
leading - the template strand of the original dna
lagging - the strand created during DNA replication
Descirbe Meselson and Stahl’s experiment?
DNA grown in N-15 broth then moved to N-14.
New DNA contained both 15 and 14 Nitrogen proving that semi conservative replication occured
describe the 5 types of mutations
insertion (frame shift) … knock-on effect, changing the triplets further on
deletion (frame shift) - changes every triplet further on
substitution -only change the amino acid for the triplet in which the mutation occurs
duplication - one or more copies of the gene / region of a chromosone are copied. not harmful, evolution occurs
inversion -single gene is split in 2 and one piece is flipped 180º
what is a gene mutation
a spontaneous change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
what is CF caused by
a recessive allele of the CFTR gene.
mutation in the cftr gene leads to production of non functional chloride channels
this reduces movement of water by osmosis, results in body producing large amounts of thick sticky mucus.
problems of the respiratory system in CF patients
due to faulty chloride ion channels, the cilia are unable to move as the mucus is so sticky and thick … lung infections occur more freq
mucus build up in lungs decreases SA for gas exchange … rate is decreased
what issues can CF patients have in the digestive system?
tube to the pancreas can become blocked, preventing digestive enzymes from entering the small intestine … key nutrients may not be made available for absorption
mucus can cause cysts which inhibit the production of enzymes further
and inhibit the absorption of nutrients in the blood
what issues can CF patients have in the reproductive system? men y women
men = tubes of testes become blocked, preventing sperm from reaching the penis
women = thickened cervical mucus can prevent sperm reaching the oviduct to fertilise an egg
benefits of carrier testing
- families can make informed decisions before having children
benefits of preimplantation genetic diagnosis
analysis of the embryo dna prior to implanting it into the uterus
-reduces the chances of having a baby with a genetic disorder
- avoids abortion
describe the 2 types of prenatal testing
- chorionic villus sampling
8-12 weeks
removal of placenta tissue through the abdomen or vagina
1-2% risk of miscarriage - aminocentesis
15-17 weeks
inserts a needle into amniotic fluid which contains fetal cells which contain DNA
1% risk of miscarriage - non-invasive prenatal diagnosis
7-9 weeks
analyses blood plasma
benefits of prenatal testing
allows parents to make informed decisions
and prepare for future care of child
treatments for CF
Bronchodilators, antibiotics, DNAase enzymes, steroids.
Change in diet.
Enzyme supplements.
Physiotherapy.
Transplants
Gene therapy.
What is gene therapy
Desired gene is inserted into a vector
modified dna put into a human cell
produces a functional protein
what is the mutation in sickle cell anaemia
- substitution mutation
- adenine replaces thymine
results in non polar amino acid Valine being coded instead of polar amino acid Glutamic acid - causes haemoglobin to be less soluble
- red blood cells are sickle shaped so carry less oxygen
