Topic 2 completed Flashcards
define diffusion
the net movement of particles from an area of high to low concentration
is diffusion active or passive?
passive- no energy needed
what 3 things increase gas exchange?
high surface area to volume ratio, short diffusion distance, and high concentration gradients
how are the lungs adapted for gas exchange?
-lots of alveoli for large surface area
-alveolar epithelium and capillary endothelium are both 1 cell thick (short diffusion pathway)
-alveoli have good blood supply so maintain concentration gradients of gases
-constant breathing keeps concentration gradients constant
what is Fick’s Law?
rate of diffusion∝ area of diffusion surface x difference in concentration / diffusion distance
what model is used to describe the cell membrane?
fluid mosaic model
what is the layer in a cell membrane?
phospholipid bilayer
what is a phospholipid bilayer made of?
hydrophilic phosphate heads and hydrophobic fatty acid tails
how is the phospholipid bilayer arranged?
fatty acid tails on the inside and phosphate heads on the outside
what 5 additional things can be found in the cell membrane?
glycolipids, glycoproteins, cholesterol, protein channels, proteins
what is the role of cholesterol in the plasma membrane?
regulates membrane fluidity by binding to the hydrophobic tails to pack them closely together in high temps (increases stability) or by stopping the phosphate tails being to close together in low temps (increases fluidity)
what are the roles of glycoproteins and glycolipids in the plasma membrane?
bind with substances such as hormones at the cells surface and some act as antigens for cell-to-cell recognition
how permeable is the plasma membrane?
partially permeable- small molecules can move through gaps but large molecules or ions cannot
define osmosis
diffusion of water molecules across a partially permeable membrane from high to low water concentration (low solute to high solute concentration)
define diffusion
the net movement of a substance from an area of high to low concentration- passive (small and non-polar molecules)
what is facilitated diffusion?
large and/or charged particles use carrier or channel proteins to move through the cell membrane- down concentration- passive process
how do carrier proteins work?
large and/or changed molecule attaches to protein in membrane, protein changes shape, molecule released to opposite side of membrane
how do channel proteins work?
charged molecule diffuses down pores created by channel proteins through membrane (control movement of ions as usually voltage gated)
define active transport
the movement of molecules through a partially permeable membrane from an area of low concentration to an area of high concentration
how does active transport work?
molecule attaches to carrier protein, ATP is hydrolysed which releases energy used to change the shape of the protein, protein changes shape, molecule released on other side
define endocytosis
plasma membrane surrounds large molecule, membrane pinches off to form a vesicle (containing the molecule) inside the cell- active process
describe exocytosis
vesicles pinch off from the sacs of the Golgi apparatus and move towards membrane, vesicle fuses with membrane and content is released- active process
how do the largest molecules such as carbohydrates, lipids etc enter and leave the cell?
endo and exocytosis
what is the difference between facilitated diffusion and active transport?
diffusion both carrier and channel proteins, active transport only uses carrier proteins. facilities diffusion is down concentration gradient but active transport is against the concentration gradient
what is an animo acid made of?
a carboxyl group, amine group, H and an R group
how are polypeptides formed?
two amino acids join together in a condensation reaction to lose a water molecule and form a polypeptide bond
what is the primary structure of a protein?
sequence of amino acids in the polypeptide chain
what is the secondary structure of a protein?
hydrogen bonds form alpha helix or beta pleated sheets between the polypeptide chains
what is the tertiary structure of a protein?
extra bonds such as ionic, hydrophobic &hydrophilic interactions or disulphide form, this is the final 3D structure
what is the quaternary structure of a protein?
the way several polypeptide chains are held together (more than one chain)
are globular or fibrous proteins soluble?
globular
why are globular proteins soluble?
hydrophilic parts of chain on the outside and hydrophobic parts of chain on the inside
describe the shape of a globular protein
round, compact, multiple chains
where are fibrous tissues found?
in connective tissue
describe the structure of a fibrous protein
long, insoluble polypeptide chain that are tightly coiled round each other to form a role like shape
are globular or fibrous proteins insoluble?
fibrous
what type of protein is haemoglobin?
globular
describe haemoglobin
a globular protein, 4 polypeptide chains, carries oxygen, soluble, contains iron-containing haem groups that bind to oxygen
what type of protein is collagen?
fibrous
which type of protein is strong and why?
fibrous because the chains are held together with lots of bonds including hydrogen and disulphide
what are enzymes?
biological catalysts
what is the difference between catabolic and anabolic enzymes?
catabolic enzymes break down molecules (exothermic), anabolic enzymes form molecules (endothermic)
what are the 2 types of enzymes?
extracellular (catalyse reactions outside the cell) and intracellular (catalyse reactions inside the cell)
what are the 2 models for enzyme activity?
lock and fit, and induced fit
how is the induced fit model different to the lock and key model?
in the lock and key, neither the enzyme nor the substrate change shape but in the induced fit model the substrate has to change the shape of the active site in the correct way
how does enzyme concentration affect rate of reaction?
the more enzyme molecules, the more active sites and therefore the more likely a substrate molecule is to collide with an active site and form a complex. If substrate concentration is limited there comes a point that no more complexes can form as not enough substrate.
how does substrate concentration affect rate of reaction?
the more substrate, the more frequent successful collisions and rate increases. until all active sites are full and enzymes become limiting factor
in a nucleotide, what does the oval, pentagon and rectangle represent?
oval= phosphate
pentagon= sugar (ribose or deoxyribose)
rectangle= base
what are the bases in DNA?
adenine, thymine, cytosine, guanine
what are the bases in RNA?
adenine, uracil, cytosine, guanine
what type of bond is between a sugar of one nucleotide and a phosphate of another?
phosphodiester (from condensation reactions)
what type of bond is between the sugar and the base of the nucleotide?
glycosidic
what are the purine bases?
adenine and guanine
what are the pyrimidine bases?
cytosine, thymine and uracil
how many hydrogen bonds between A and T?
2 hydrogen bonds
how many hydrogen bonds between C and G?
3 hydrogen bonds
what sort of pairing is between bases?
complementary base pairing
what makes up a DNA double helix?
2 antiparallel polynucleotide strands twisted together
describe the role of mRNA
messenger RNA-
made in the nucleus during transcription
carries genetic code from DNA in nucleus to cytoplasm
describe tRNA
transfer RNA-
in cytoplasm
has an amino acid binding site, and a sequence of 3 bases (anticodon)
attaches to one of the amino acids that are used to make proteins to the ribosomes during translation
the genetic code is non-overlapping, what does this mean?
each triplet is read in sequence and separate from the triplets either side
the genetic code is degenerate, what does this mean?
some amino acids are coded for by more than one codon (more possible combinations of triplets than amino acids)
what are the steps of transcription?
-RNA polymerase attaches to DNA
-DNA unwinds due to H bonds breaking
-template strand is used to make mRNA using free floating mononucleotides (phosphodiester bonds form from condensation reactions)
-RNA polymerase reaches stop codon and
hydrogen bonds reform
-mRNA moves out of nuclear pore and to a ribosome in the cytoplasm
what are the steps of translation?
-mRNA attaches to ribosome
-tRNA attaches to specific amino acids and they move to ribosome
-the tRNA with an anticodon complementary to the start codon attaches to mRNA
-second tRNA does the same
-the 2 amino acids on the tRNA molecules join together to start a polypeptide chain
-once the tRNA molecules are empty they move away
-this continues until a stop codon is reached
what are the steps of semi-conservative replication?
-DNA helicase breaks hydrogen bonds and DNA unwinds
-both strands act as template strands
-free-floating DNA nucleotides are attracted to exposed bases
-condensation reactions join DNA mono-nucleotides together
-hydrogen bonds form between bases
-2 DNA molecules are produced each with 1 new and 1 old strand
who provided evidence for semi-conservative replication?
Meselson and Stahl
what is the first stage of Meselson and Stahl experiment?
grow 2 samples of bacteria, one in N14 and one in N15
In the Meselson and Stahl experiment, why do the DNA become different weights?
when growing, the bacteria take up the nitrogen into nucleotides for new DNA- the nitrogen are different weights
In the Meselson and Stahl experiment, during the first spin what is shown?
The DNA from the heavy nitrogen settled lower than the DNA from the light nitrogen
in the Meselson and Stahl experiment what happens after the first spin?
the bacteria with heavy DNA is put in the light nitrogen for one replication and spun again
In the Meselson and Stahl experiment what does the second spin show?
the new DNA has one heavy and one light strand and so settled in the middle of the light and heavy DNA
what is the role of DNA polymerase in DNA replication?
catalyses condensation reactions between DNA nucleotides to form phosphodiester bonds
what is the role of DNA helicase in DNA replication?
breaks the hydrogen bonds between the bases to unzip the DNA
define mutation
changes in the base sequence of DNA
what are the 5 types of mutation of DNA?
substitution, deletion, insertion, duplication and inversion
what is a substitution mutation?
one base is substituted for another
what is a deletion mutation?
one base is deleted- creates a frame shift
what is an insertion mutation?
an extra base is added- creates a frame shift
what is a duplication mutation?
one or more bases are repeated
what is an inversion mutation?
a sequence of bases is reversed
define gene
a sequence of bases on a DNA molecule, that codes for a sequence of amino acids in a polypeptide chain
define allele
a different version of a gene (slightly different base sequences so code for different versions of the same characteristic)
define genotype
the alleles a person has
define phenotype
the characteristics displayed by an organism
define dominant
an allele whose characteristic appears in the phenotype even if there’s only one copy
define recessive
an allele whose characteristic only appears in the phenotype if 2 copies are present
define incomplete dominance
when the trait from a dominant allele isn’t completely shown over the trait produced by the recessive allele, so both alleles influence phenotype
define homozygote
an organism that carries 2 copies of the same allele for a certain characteristic
define heterozygote
an organism that carries 2 different alleles for a certain characteristic
define carrier
if a recessive allele can cause disease, a carrier is someone who dominant and one recessive allele
what is an inherited recessive disorder?
caused by a faulty allele
that is only expressed in the absence of a normal allele (homozygous recessive)
what is monohybrid inheritance?
the inheritance of a single characteristic controlled by different alleles
what does chi-squared test?
used to see if the results support a theory by seeing if there is a significant difference between the observed and expected values (to see if the null hypothesis will be accepted or rejected)
when using chi-squared, to reject the null which number has to be larger?
the x squared number (the number you worked out) has to be larger than the critical value at the 5% significant level
what allele is cystic fibrosis caused by?
a recessive allele
what causes cystic fibrosis?
CFTR (cystic fibrosis transmembrane conductance regular) protein being less efficient
what is CFTR?
a channel protein that transports chloride ions out of the cell and into mucus
which chromosome is the CFTR gene on?
chromosome 7
how does the mutant CFTR protein cause thick sticky mucus?
the mutant protein is less efficient at transporting chloride ions out of the cells (through the basal membrane), so less water moves out by osmosis
What 3 systems are affected by cystic fibrosis?
respiratory, digestive, reproductive
how does sticky mucus affect the respiratory system?
cilia are not able to move mucus so it builds up in airways, some airways can become completely blocked. This reduces surface area for gas exchange and causes breathing issues
people with CF also more prone to lung infections as mucus containing microorganisms can not be removed
how does sticky mucus affect the digestive system?
the tube that connects the pancreas to the small intestine can become blocked- this prevents digestive enzymes produced by the pancreas reaching the small intestine (fewer nutrients are absorbed)
the mucus can cause cysts to form in the pancreas inhibiting the production of enzymes which reduces digestion and absorption of nutrients
the mucus lining of the small intestine is abnormally thick (fewer nutrients absorbed)
how does sticky mucus affect the reproductive system in females?
thicken cervical mucus can prevent the sperm form reaching the egg as the mucus reduces the mobility of the sperm
how does sticky mucus affect the reproductive system in males?
the vas deferens (sperm duct) gets blocked (or is absent) with mucus so sperm cannot leave the testes
what does genetic screening involve?
analyses DNA to see if it contains alleles for genetic disorders
what are the 3 uses of genetic screening?
identification of carriers, preimplantation genetic diagnosis, prenatal testing
what are the ethical issues of carrier testing?
finding out you’re a carrier may cause emotional stress or affect your ability to find a partner
tests aren’t 100%- false results possible
other genetic abnormalities could be found which could cause stress
there are concerns that life insurance companies or employers may use the results, causing genetic discrimination
what are the positives of carrier testing?
offered to people with a family history of genetic disorders so they can determine the chances of any future children having the disease
allows people to make informed decisions
what is Preimplantation genetic diagnosis?
screens embryos for genetic disorders before they are implanted
what are the positives of preimplantation genetic diagnosis?
reduces chance of having a baby with the genetic disorder as embryos with the allele for the disorder will not be implanted
avoids potential need for abortion
what are the issues with preimplantation genetic diagnosis?
can be used to find out other features such as eye colour and may lead to designer babies
false results possible- lead to destruction of healthy embryos
what is prenatal testing?
screens foetuses for genetic disorders and are offered to women with a history of genetic disease
what are the 2 types of prenatal testing?
chorionic villus sampling (CVS) and amniocentesis
when is amniocentesis carried out?
15-20 weeks of pregnancy
what is amniocentesis?
A sample of amniotic fluid is obtained using a needle
the fluid contains fetal cells which contain DNA which can be analysed
what are the disadvantages of amniocentesis?
1% risk of miscarriage
takes time- rapid test 3-4 days
full results- 2-3 weeks
when is chorionic villus sampling carried out?
11-14 weeks of pregnancy
what is chorionic villus sampling?
a sample of cells is taken from the chorionic villi using a needle and the DNA within the cells is analysed
what are the advantages of chorionic villus sampling?
takes place sooner than amniocentesis so more time to make decisons
what are the disadvantages of chorionic villus sampling?
1-2% risk of miscarriage
in depth results take at least 2 weeks
