Genes & Health Flashcards
Topic 2
Give the general structure of an amino acid.
Describe the primary structure of a protein.
The specific sequence of amino acids in a polypeptide chain joined together by peptide bonds in condensation reactions.
Describe the secondary structure of a protein.
polypeptide chain coils into alpha helixes caused by hydrogen bonds or folds into beta pleated sheets.
Describe the tertiary structure of a protein.
Further folding of the secondary structure into a specific 3D shape. Held together by bonds between amino acid R groups.
Disulphide, ionic or hydrogen bonds formed.
Describe the quaternary structure of a protein.
3D arrangement involving more than one polypeptide chain.
Describe the importance of a protein’s primary structure in determining its 3D structure.
The primary structure (sequence of amino acids in a polypeptide chain), determines the position of amino acid R groups. Hydrogen, ionic and disulphide bonds can form between these R groups. These bonds determine how a polypeptide chain folds into a specific 3D shape, forming a protein. The specific 3D shape of a protein gives the protein specific properties and allows it to carry out a specific function.
Describe globular proteins.
Polypeptide chains made of many amino acids are folded into a compact spherical shape. Have a tertiary of quaternary structure. Have hydrophilic R groups on outside and hydrophobic R groups on inside. They are soluble. e.g. haemoglobin, enzymes - thrombin.
Describe fibrous proteins.
Polypeptide chains made up of many amino acids remain elongated. Little or no tertiary structure. Has repetitive sequence of amino acids. Fibrous proteins are long chains that are strong and cross-linked. Have hydrophobic R groups on outside - insoluble.
e.g. collagen, fibrin, keratin
Describe a conjugated protein.
Proteins with another chemical (prosthetic/ non-protein) group associated with their polypeptide chain/s.
e.g. haemoglobin, glycoproteins and lipoprotein.
Where are the polar R groups found in a protein and why?
Found on the outside surface of the protein because they are hydrophilic therefore are attracted to other polar molecules.
Where are the non-polar R groups found in a protein and why?
Found on the inside of the protein because they are hydrophobic therefore repel other polar molecules.
Describe haemoglobin.
Globular protein with 4 polypeptide chains. Quaternary structure. Conjugated protein - had haem group attached. Soluble. Function: binds O2 in red bloods cells for O2 transport.
Describe collagen.
Fibrous protein with 3 polypeptide chains coiled around each other. Quaternary structure. Insoluble. Cross linking between chains. Provides strength and flexibility.
Name the 7 components of the Fluid Mosaic Model.
Proteins, glycolipids, glycoproteins, phospholipids, carrier channel (transmembrane) proteins, cholesterol, carbohydrates
Give two properties of cell membranes.
Fluid and therefore flexible.
Selectively/ partially permeable.
Describe the phospholipid bilayer.
Phosphate heads are polar and hydrophilic so associate with water. Fatty acid tails are non-polar and hydrophobic so repel water.
Describe the structure of a phospholipid.
Phosphate head group and two fatty acids joined by a glycerol backbone by ester bonds.
Name the three passive transport processes.
Diffusion, Osmosis, Facilitated Diffusion
Name the three active transport processes.
Active transport, Exocytosis, Endocytosis
Define diffusion.
Net movement from an area of high concentration to an area of low concentration, down a concentration gradient.
Define facilitated diffusion.
Movement from an area of high concentration to an area of low concentration, through carrier or channel proteins.
Define osmosis.
Net movement of water molecules from an area of low solute concentration to an area of high solute concentration through a partially permeable membrane. Continues until isotonic.
Define active transport.
Movement from an area of low concentration to an area of high concentration through a carrier protein using ATP energy.
Define exocytosis.
Bulk transport out of a cell. A membrane bound vesicle, with the substance inside, fuses with the cell membrane and the vesicle membrane becomes part of the cell membrane, releasing the substance.
Define endocytosis.
Bulk transport into a cell. The cell membrane invaginates (bulges inwards) to form a vesicle which pinches off, enclosing the substance.
Describe structure of DNA.
DNA mononucleotides are joined together by phosphodiester bonds in condensation reactions, to form two long polynucleotide chains (DNA strands). The two DNA strands twist around each other forming a double helix and are joined by hydrogen bonds between bases, which hold the two strands together. DNA is a nucleic acid.
Describe the structure of a mononucleotide.
Organic nitrogen containing base (A,T,C or G) and phosphate group attached to deoxyribose pentose sugar.
Describe the complementary base pairing in DNA.
Adenine always pairs with Thymine and there are 2 hydrogen bonds between bases.
Guanine always pairs with Cytosine and there are 3 hydrogen bonds between bases.
Describe RNA.
Made up of a phosphate, a ribose sugar and a nitrogenous base of adenine, uracil, guanine and cytosine.
Compare and contrast the structures of DNA and RNA.
Similarites:
- The mononucleotides are joined by phosphodiester bonds in condensation reactions.
- Both made of mononucleotides composed of phosphate, a pentose suagr and an organic base.
- They both share three bases that are the same - adenine, guanine, cytosine.
Differences:
- DNA is double stranded whereas RNA is single stranded.
- DNA has thymine whereas RNA has uracil.
- The sugar in DNA whereas in RNA it is ribose.
Describe DNA replication.
Enzyme DNA helicase breaks the hydrogen bonds between two DNA strands. Both DNA strands act as templates. Free mono nucleotides line up along both DNA strands and complementary base paring occurs. Hydrogen bonds form between bases to join the two DNA strands. Enzyme DNA polymerase joins adjacent mononucleotides with phosphodiester bonds in condensation reactions. Enzyme ligase follows and glues fragments together. (Semi-conservative replication).
Name the two stages of protein synthesis.
Transcription and Translation.
Describe transcription.
Enzyme DNA helicase unzips the double helix, exposing the two strands by breaking the hydrogen bonds between the bases. Anti-sense strand of DNA is used as template. Enzyme RNA polymerase base pairs free complementary nucleotides with phosphodiester bonds, forming the coding strand, which produces a single strand of RNA (mRNA).
Occurs in nucleus
Describe translation.
- mRNA leaves the nucleus and attaches to the ribosomes in the cytoplasm.
- Each tRNA attaches to a specific amino acid and carries it to the ribosome
- Complementary base pairing takes place between the anticodon on tRNA and the codon on mRNA
- A peptide bond forms between amino acids in a condensation reaction
- The ribosome moves along mRNA and detaches from mRNA at a stop codon
- The completed polypeptide chain detaches from the ribosome
Translation is caused by a start and a stop codon.
The code is non overlapping and degenerate.
Occurs in ribosome in cytoplasm
Describe the nature of the genetic code.
- triplet code: three bases code for one amino acid
- non-overlapping: each base is only part of one triplet
- degnerate: more than one triplet code can code for the same (one) amino acid
- universal
Describe the role of tRNA.
- each tRNA brings a specific amino acids to the ribosomes
- The tRNA with the complementary anticodons binds to the mRNA codon
- tRNA binds to the ribosomes
What is a mutation?
A gene mutation is a change in the base sequence of DNA in a gene.
What are the different types of mutations?
- Substitution: a base has been changed for a different one - changes one DNA triplet in DNA.
- Addition/ insertion: base/s added into the DNA, usually causing a frameshift which changes all subsequent triplets.
- Deletion base/s in the DNA deleted, usually causing a frameshift – changes all subsequent triplets.
Distinguish between germ line and somatic mutations.
- Germ line mutations occurs in replicating DNA of ovaries or testes in the creation of ovum or sperm, whereas somatic mutation occur in body cells after conception.
- In germ line mutations the mutation is passed on to offspring and can cause an inherited genetic disorder, whereas in somatic mutation the mutation is not passed on to offspring.
Explain how mutation changes function of protein e.g. enzyme.
- Mutation results in a change in base sequence of DNA.
- So there is a change in primary structure.
- So change in position of the ionic bonds so protein is folded differently.
- Therefore this causes a change in enzyme shape/ active site.
- So no enzyme-substrate complexes can be formed.
What type of protein is the CFTR protein?
A channel protein
Where is the CFTR protein found in the human body?
In the apical membrane of mucus producing cells/epithelial cells of respiratory/digestive/reproductive systems.
What is the role of the CFTR protein?
Responsible for transporting chloride ions (Cl-) through cell membranes.
Describe the effects of faulty CFTR protein being produced.
- The faulty CFTR protein cannot transport chloride ions, so these ions cannot move out of epithelial cells through the CFTR protein to enter mucus
- Therefore sodium ions do not move out of cells and into the mucus, and consequently water cannot move out of cells into mucus by the process of osmosis
- Mucus becomes thicker/ stickier/ more viscous than normal, blocking parts of the body, which impairs the functioning of the respiratory, digestive and reproductive systems
What is the role of mucus in the lungs and how is it removed from the lungs?
- Traps dust, debris and microorganisms
- Cilia in the epithelial cell lining of the respiratory system (trachea and bronchi) continually remove the mucus by a wave-like beating. Mucus is then coughed up and removed or swallowed. Stomach acid (hydrochloric acid) destroys the pathogens.
How does stickier mucus in people with CF reduce gas exchange.
Thicker and sticker mucus cannot be moved by cilia , so mucus remains in the lungs and blocks the bronchioles , restricting airflow through these tubes which prevents the ventilation of the alveoli below the blockage. This reduces the number of alveoli involved in gas exchange, which reduces the surface area, leading to reduced gas exchange. It also reduces the concentration gradient for oxygen and carbon dioxide diffusion, which also reduces gas exchange. Blockages can also cause over-inflation of alveoli, which can cause damage to the elasticity of the lungs.
Why do people with CF get short of breath?
Reduction in gas exchange results in a lower oxygen supply to the cells and tissues. This means during exercise the muscle cells receive less oxygen.
How does CFTR lead to persistent lung infections?
Cilia cannot move mucus, so mucus builds up in the lungs. Anaerobic bacteria which enter the lungs rapidly multiply in the mucus, due to the lack of oxygen in the mucus, causing a lung infection. White blood cells, which try to kill the bacteria, die and break down releasing DNA which makes the mucus even stickier. Repeated infections damage the lung tissue.
Describe what happens when there is extra water in the mucus.
Sodium is transported across the basal membrane and diffuses through sodium channels. Chlorine diffuses down an electrical gradient. Water is drawn out of cells due to the high salt concentration and then drawn out of the mucus.
Describe what happens when there is too little water in the mucus.
Chlorine is transported across the basal membrane and diffuses through an open CFTR channel. Sodium diffuses down an electrical gradient. Water is drawn out of the cell and into the mucus.
Describe what happens in cystic fibrosis sufferers.
CFTR channel is absent or dysfunctional. Sodium channel is permanently open. Water is constantly being removed from mucus. Mucus becomes thicker, stickier and viscous.
Describe the effect of cystic fibrosis on the digestive system.
Pancreatic duct blocked with thick, sticky mucus, prevents release of digestive enzymes, food is not digested properly, resulting in malabsorption syndrome. Lack of glucose delivered to body cells for respiration, results in a lack of energy for cell activity, resulting in tiredness.
Describe the effect of cystic fibrosis on the pancreas.
Stickier mucus blocks the pancreatic duct, so pancreatic enzymes become trapped in the pancreas, behind the mucus and can damage the pancreas and produce cysts of hard fibrous tissue. If cells that produce the hormone insulin , are damaged, this can result in a form of diabetes.
Describe the effect of cystic fibrosis on the reproductive system.
- Females are less likely to become pregnant due to a mucus plug in the cervix caused by viscous mucus.
- Males may have a mucus plug in the vas deferens or may lack the vas deferent due to the viscous mucus which blocks the sperm duct and prevents sperm from being released.
Describe how the lungs are adapted for rapid gas exchange.
- many alveoli provide a large surface area to volume ratio for gas exchange.
- alveoli/ capillary walls are one cell thick enabling a short diffusion pathway.
- ventilation of the alveoli maintains a steep concentration gradient.
- extensive capillary network around alveoli provides large surface area for gas exchange.
Define biological catalyst.
A molecule produced by an organism/cell, which speeds up the rate of a biological reaction by reducing the activation energy and is not used up in the reaction.
Define activation energy.
Energy needed for a reaction to occur, by causing bonds to break / form and which is reduced by enzymes.
Describe the structure of an enzyme.
An enzyme is a globular protein, so has tertiary structure held together by ionic, hydrogen and disulphide bonds between R groups, giving it a spherical shape. An enzyme also has hydrophilic amino acids on the outside and hydrophobic amino acids on the inside. An enzyme also has an active site, which is a specific shape to fit the shape of a specific substrate.
Describe the mechanism of enzyme action (how an enzyme works).
- The substrate fits into and binds to the enzyme active site.
- The shape of the active site fits the shape of the substrate – lock and key theory or induced fit theory
- An enzyme-substrate complex forms and the substrate is held in the correct position for bonds to be broken or formed, and product to be made. This lowers the activation energy for the reaction.
- The product is released from the active site and the enzyme is unchanged/not used up and is therefore free to accept another substrate molecule
Explain why an enzyme can only catalyse one reaction (has one substrate).
- Enzyme has a specific tertiary structure/ is specific/ has a specific substrate
- Due to the specific shape of active site
- Only the substrate will fit into the active site / explanation of ‘lock and key’, where enzyme is lock and substrate is the key
- To form an enzyme-substrate complex
- Another substrate has a different shape
Distinguish between an intracellular enzyme and an extracellular enzyme.
Intracellular enzymes catalyse reactions inside cells, but extracellular enzymes catalyse reactions outside cells.
Explain the effect of increasing enzyme concentration on the rate of reaction.
As the enzyme concentration increases, the initial rate of reaction increases because the number of enzymes increases, so the number of avaliable active sites increases. This leads to more frequent successful collisions between the enzyme and the substrate, forming more enzyme-substrate complexes and therefore more product in a given time. The enzyme concentration is the limiting factor.
Eventually the reaction slows down and the rate becomes constant /reaches a plateau, as the substrate concentration becomes the limiting factor. Now all the enzyme active sites are occupied, so adding more enzymes has no further effect on rate.
Explain the effect of increasing substrate concentration on the rate of reaction.
As the substrate concentration increases, the initial rate of reaction increases, as there are more frequent successful collisions between the enzyme and the substrate, forming more enzyme-substrate complexes and therefore more product in a given time. The substrate concentration is the limiting factor.
Eventually the reaction slows down, as the substrate is decreasing, so there are fewer collisions between enzyme and substrate . The rate becomes constant /reaches a plateau. The enzyme concentration has become the limiting factor. Every active site is occupied, so substrate molecules cannot enter an active site until one becomes free again. This means that increasing substrate concentration further has no effect on the rate - saturation point.
Explain the effect of increasing temperature on the rate of reaction/enzyme activity.
- At low temperatures enzymes are inactive as they have low kinetic energy, so there are fewer collisions between enzyme and substrate so the rate of reaction is slow. As temperature increases, the rate of reaction increases, as the kinetic energy of the enzyme and substrate increases, so there are more frequent successful collisions between enzyme and substrate.
- At the optimum temperature the rate of reaction is at its fastest/highest, as there are maximum successful collisions between enzyme and substrate.
- At temperatures above optimum the rate of reaction decreases , as enzymes become denatured and active sites change shape, so the substrate cannot fit into the active site and enzyme-substrate complexes and product cannnot form.
Define gene.
A sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain.
Define allele.
Alternative forms of a gene found at the same locus on a chromosome.
Define genotype.
The alleles in an organism, for a particular gene.
Define phenotype.
The observable characteristic, due to the expression of a genotype/alleles, which may be affected by the environment.
Define recessive allele.
Both alleles need to be present in order for the recessive phenotype to be observed (only expressed if the dominant allele is not present).
Define dominant allele.
Only one allele needs to be present for the dominant phenotype to be observed.
Define incomplete dominance.
When there are two different alleles in the genotypes and both alleles are expressed in the phenotype of the organism - both alleles have an equal weighting in the expression.
Define homozygous.
A genotype where both alleles present at a gene locus are the same.
Define heterozygous.
A genotype where both alleles present at a gene locus are different.
Define homologous chromosomes.
A pair of chromosomes, similar in length, with the centimetre and genes in the same position.
Define gene locus.
The position of an allele on a chromosome.
Define carrier.
An organism with a heterozygous genotype. They have one allele for a condition/ characteristic, but it is not expressed in the phenotype.
Define monohybrid inheritance
Inheritance of one gene is responsible for the expression of the genotype.
What are the 3 types of pre-natal screening?
Amniocentesis, chorionic villus sampling, NIPD.
Describe amniocentesis.
Carried out when fetus is in uterus at 15-17 weeks. Fetal cells collected from the amniotic fluid surrounding fetus using a needle into the abdomen - dna extracted and analysed to detect gene mutation. 0.5-1% risk of miscarriage.
Describe chorionic villus sampling (CVS).
Carried out when fetus is in uterus between 8-12 weeks. Fetal cells are collected from the placenta using a needle into abdomen or cervix into uterus via vagina - dna extracted and analysed to detect gene mutation. 1-2% risk of miscarriage.
Describe non-invasive prenatal diagnosis (NIPD).
Carried out when fetus is in the uterus between 7-9 weeks. Analyses DNA fragments (cell free fetal DNA) from the mothers blood plasma to detect gene mutation.
Describe pre-implantation genetic diagnosis (PGD).
Carried out during 8 cell embryo stage in IVF. One cell is taken from the embryo and dna is extracted and analysed to detect gene mutation.
Describe the disadvantages/ implications of genetic screening.
Risk of miscarriage (amniocentesis + CVS)
False positive result could results in abortion of a healthy fetus.
Emotional and physical stress of choosing an abortion.
