Unit One Flashcards
What are non-coding RNA genes
Genes that do not code for proteins
What are some factors that can make a cell vary the proteins expressed
Metabolic activity
Cellular stress
Responded to signalling molecules
Diseased cells
Eukaryotic cells have plasma membrane:
What is a eukaryotic cell and what is the plasma membrane
- A cell with a nucleus
- The boundary around the outside of the cell
What is another trait of a eukaryotic cell
not plasma membrane or nucleus
They have internal membranes to increase the total area of the membrane
What does the size of a eukaryotic cells mean
They will have a small surface area to volume ratio. And therefore too small to carry out all the vital functions carried out by membranes
What are other cells that have membranes
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vesicles
The endoplasmic reticulum (ER) forms a network of tubules with the nuclear membrane what are the two types of tubules and their differences
Rough endoplamsic reticulum (RER)-Rough the ribosomes are on the outside of the cystolic face.
Smooth endoplasmic reticulum (SER)- lacks ribosomes
What is the Golgi apparatus
A series of flattened discs
What is a lysosome
They are a membrane bound to organelles containing variety of hydrolases that digest
Proteins
Lipids
Nuclei acid
And carbohydrates
What is a hydrolases
They are enzymes that catalase the cleavage of a covalent bond bond using water
what does a vesicle do
Transport materials between compartments
What are membranes made of
They are made of proteins and lipids
Where are lipids synthesised
In the smooth endoplasmic reticulum (SER) and insterted into the membrane
Where does the beginning of protein synthesis occur
In the cytosolic ribosomes but the location of the end process is completed is depended on the protein being made
what do multicellular organisms use to signal between cells
extracellular signalling molecules
what is an extracellular signalling molecule (examples)
steroid hormones
peptide hormones
neurotransmitters
describe nervous communication
electrical impulses and neurotransmiters
transported along neurons
faster response
transient response
localised extent of response
describe hormonal communication
hormones signal
bloodstream transmission
targets almost any cells in the body
slower response
longer duration response
widespread response
what causes a conformational change of a receptor
binding at site for a specific signal molecule
why do signalling molecules have different effects on different target cell
due to differences in the intracellular signalling molecules and pathways that are involved
in multicellular organisms different cell types may show what
tissue specific response to the same signal
describe hydrophobic signals
they can diffuse directly through the phospholipid bilayers of membranes they bind to intracellular receptors in the cytosol
why are hydrophobic signals able to diffuse through phospholipid bilayers
the tails of the phospholipids in the plasma membrane are both hydrophobic to allow for the molecules to pass.
what are the receptors for hydrophobic signalling molecules
transcription factors
what is a transcription factor
proteins that when bound to DNA can inhibit or stimulate initiation of transcription, can enhance or block binding of RNA polymerase to specific genes. control whether the gene is transcribed and therefore expressed
what are example of hydrophobic signals
steroid hormones (oestrogen and testosterone )
where do steroid hormones bind (2)
1.specific receptors in the cytosol
- the nucleus forming-receptor complex
What happens when the hormone receptor complex moves to the nucleus
binds to specific sites on DNA
what is the hormone response element
(HRE)
the specific DNA sequences that the hormone-receptor complex binds to
what does binding at HRE influence
influences the rate of transcription, and gene expression
describe hydrophilic signalling
bind to transmembrane receptors and DONT enter cytosol
not capable of passing across hydrophilic plasma membrane
examples of hydrophilic signalling
peptide hormones
neurotransmitters
describe a ligand
hydrophilic signalling molecule that binds to another molecule
when ligands bind to the extracellular face what changes conformation
trans-membrane receptors
What are the three key steps of hydrophobic signalling
reception
transduction
response
describe reception in hydrophilic signalling
signalling molecule binds to trans-membrane receptor
describe transduction in hydrophilic signalling
signal is passed through the cell
describes response in hydrophilic signalling
will vary depending on the signal.
What causes altered behavior of the cell in hydrophilic signal receptors
trans-membrane receptors act as signal transducers by converting the extracellular ligand-binding event into intracellular signals
what do transduced hydrophilic signals involve
g-proteins
cascades of phosphorylation by kinase enzymes
describe G-proteins
relay signals from activated receptors to target proteins such as enzyme and ion channels
describe cascades of phosphorylation
one kinase activates the next in the sequence.
They can result in the phosphorylation of many proteins as a result of the original signalling event.
They can allow for more than one intracellular signalling pathway to be activated
what hormones are involved in glucose blood levels
insulin
glucagon
features of insulin
made as a result of increased glucose in blood
made in pancreas
hydrophilic peptide hormone
allows for tissue and skeletal muscles to absorb glucose from the bloodstream
how does glucose pass into cells
through a transporter protein called GLUT4 by facilitated diffusion
describe type one diabetes
detected in early years
caused by a failure to produce insulin
treated by regular insulin injections throughout the day
describe type two diabetes
caused by being overweight or inactive
discovered later in life
loss of insulin receptor function
lifestyle changes
exercise triggers recruitment of GLUT4 so can improve uptake of glucose to fat and muscle cells
what is a membrane potential
(an electrical potential difference) is created when there is a difference in electrical charge on the two
sides of the membrane.
what is the resting membrane potential
a state where there is no net flow of ions across the membrane
-60 and -80mV when cell is not transmitting signals
what does a nerve transmission require
changes in the membrane potential of the
neuron’s plasma membrane nerve transmissions a wave of depolarisation of the resting potential of a neuron
what is depolarisation
is a change in the membrane potential to a less negative value inside cell
what is action potential
a wave of electrical excitation along a neuron’s plasma membrane
what are neurotransmitter receptors
ligand gated ion channels
what are the two types of photoreceptor cell in the retina
rods and cones
describe rod cells
sensitive to changes in light intensity
useful for vision in areas with low light
describe cone cells
sensitive to specific colours
allow animals to have coloured vision
what do photoreceptors of the eye contain
light-sensitive molecule-retinal
membrane protein-opsin
what is the rod cells the retinal-opsin complex called
rhodopsin
what happens in cone cells when different forms of opsin combine with retinal
they give different photoreceptor proteins with a maximal sensitivity to specific wavelengths of light
describe the plasma membrane
fluid mosaic model
allows entry and exit of materials
composed of phospholipids and proteins
describe the head region of the phospholipids
hydrophilic, polar (attracted to water)
describe the tail region of the phospholipids
hydrophobic, non-polar (repelled by water)
what kinds of proteins are there in the membrane
active transport proteins
channel forming proteins
enzymes
receptors
attachment proteins for the cell cytoskeleton
what is a cytoskeleton
The cytoskeleton gives mechanical support and shape to cells
describe integral proteins
proteins found inside the protein
some are transmembrane these span the entire length of the membrane eg. channels
they react heavily with the hydrophobic region of membrane phospholipids
region of hydrophobic R groups allow strong hydrophobic interactions that hold integral membrane proteins
describe peripheral proteins
found on the surface of the membranes have hydrophilic R groups on their surface and are bound to mem surface, by ionic and hydrogen bonds
what molecules can pass through the membrane by diffusion
small molecules such as
oxygen carbon dioxide
what are the different types of proteins involved in transporting substances
channel proteins- ligand, voltage gated
transporter proteins
protein pumps
what is facilitated diffusion
passive transport of substances across the membrane through specific transmembrane proteins
what proteins use facilitated diffusion +eg
channel proteins and transporter proteins
small intestine cells have glucose transporters
describe channel proteins
multi-subunit proteins with subunits arranged to form water filled pores that extend across the membrane.
most are highly selective
some are gated and change conformation to allow or prevent diffusion
describe gated channels
they respond to a stimulus which causes them to open or close
could be either ligand or voltage
describe ligand gated channels
controlled by binding of signal molecules
when correct signal molecules binds the gate opens allowing ions to flow through
describe voltage gated channels
controlled by changes in ion concentration
describe transporter proteins
bind to specific substance to be transported
conformational change transfer solute across the membrane
alternates between two conformational changes
so one binding site for a solute is sequentially exposed on one side of the bilayer then the other
describe protein pumps
active transport uses pump proteins that transfer substances across the membrane against their concentration gradient
pumps that carry out active transport are transporter proteins couples to an energy source
what is required for protein pumps to transfer substances
a source of metabolic energy (for active transport)
what are proteins that hydrolyse ATP directly called
ATPases
how is energy provided for the conformational change required to move substances across the membrane
active transport proteins hydrolyse ATP directly
what is an electrochemical gradient
the concentration gradient and electrical potential difference combine to form the electrochemical gradient
what is the definition concentration gradient
difference in concentration of a solute across the plasma membrane
what is the definition of electrical potential difference (aka membrane potential)
A membrane potential is created when there is a difference in electrical charge on the two sides of the membrane.
what is the sodium potassium pump also known as
Na/K-ATPase
what happens to each ATP hydrolysed
three sodium ions lebae the cell and two potassium ions are transported into the cell
what does it mean that the sodium potassium pump is foind in most animal cells
This accounts for a high proportion of the basal metabolic rate in many organisms
in the intestinal epithelial cells what is generated when the sodium potassium pump
a sodium ion gradientw
what is the glucose transporter responsible for
glucose symport transports sodium ions and glucose at the same time and in the same direction
describe lipids ; where synthesis starts, where it finishes and where the product goes
- ser
- membrane
describe cytosolic; where synthesis starts, where it finishes and where the product goes
cytosolic ribosomes
remain in cytosol
describe transmembrane proteins where synthesis starts, where it finishes and where the product goes
- RER
ER
cell membrane
what happens when the protein is made in the rer and is put into the lumen of the rer
transported by vesicles that bud off from the RER and fuse with the golgi apparatus
what happens as the proteins move through the golgi apparatus
they undergo a post-translational modification
what happens during the post-TRANSLATIONAL modification
this is when polypeptide chains have carbohydrates or phosphates added to them are cleaved (cut) to make them an active protein
the major modification is carbohydrates
what is enzymes catalyses the addition of various sugars
Lactase
what happens when a cell secretes substances and an eg.
Release to the outside peptide hormones
insulin and digestive enzymes
what is a cytoskeleton
a network of proteins throughout the cytoplasm
it also gives mechanical support and shape to cells
describe microtubules
hollow straight cylinders composed of proteins called tubulins (alpha and beta)
what does formation and breakdown of the microtubules involve
the polymerisation(growth of the microtubule) and depolymerisation (shrinkage of the microtubule) of tubulin
what do microtubules control
movement of the membrane-bound organelles and chromosomes (eg.endoplasmic reticulum )
what do microtubules do in cell division
they form spindle fibres
what is the mitotic index
percentage of cells in a sample undergoing mitosis
What is the cell cycle used for
used for growth and repair
continual process
what is the two parts cell cycle is divided into
interphase
mitotic phase
describe interphase
active period of growth
g1: a growth period
s phase: dna is replicated in prep for mitosis
G2 another growth period, proteins and organelles synthesised
mitotic phase
end of g2 cells enter mphase
this is in two stages
mitosis-chromosomal material is separated
cytokinesis- separation of the cytoplasm
describe prophase
DNA condenses into
chromosomes each consisting of two sister
chromatids. Nuclear membrane breaks down;
spindle microtubules extend from the MTOC
by polymerisation and attach to
chromosomes via their kinetochores in the
centromere region.
describe metaphase
chromosomes are aligned at
the metaphase plate (equator of the spindle).
describe anaphase
as spindle microtubules shorten
by depolymerisation, sister chromatids are
separated, and the chromosomes are pulled
to opposite poles.
describe telephase
the chromosomes decondense
and nuclear membranes are formed around
them.
what is cytokinesis
follows telephase and the cytoplasm of the cell splits to give two daughter cells
what is the function of the microtubules
aligning chromosomes on metaphase plate
separating sister chromatids
formation of daughter nuclei
describe checkpoints
mechanisms within the cell that assess the condition of the cell during the cell cycle and halt the progression to the next phase until certain requirements are met.
describe G1 checkpoints
occur towards the end of G1; sufficient cell growth must have occured before the cell can enter s phase
At the G1 checkpoint, retinoblastoma protein (Rb) acts as a tumour suppressor by
inhibiting the transcription of genes that code for proteins needed for DNA replication
describe G2 checkpoint
occurs at the end of G2; success of any DNA replication and any damage to DNA is assessed
describe the M checkpoint
occurs during metaphase and controls to entry to anaphase. progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules
Explain CDKs (3)
1cyclin proteins accumulate they are involved in cell growth and in regulating the cell cycle
2 cyclin combine and activate cyclin-dependent kinases(CDKs)
3 active cyclin-cdk complexes phosphorylate proteins that regulate progression through the cell cycle
describe retinoblastoma
is a protein that acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication
G1 CDKs phosphorylate the Rb protein. phosphorylation inhibits Rb
this allows transcription of the genes that code for proteins needed for DNA replication. cells can therefore progress from G1 to S phase
describe p53
dna damage triggers the activation of protein P53
this can stimulate DNA repair arrest cell cycle
initiate apoptosis.
descrive what it means Arrest cell cycle
this can allow time to recognise and fix the DNA damage so the cell can restart cell cycle
when is apoptosis initiated
if the dna damage is too severe
what hauses a degenerative disease
uncontrolled reduction in cell cycle rate
what causes a tumor
an uncontrolled increase in the rate of cell cycle
describe a proto-oncogene
a normal gene usually involved in the control of cell growth or division, which can mutate to form a tumour promoting oncogenes
describe amino acids
are building blocks of proteins
proteins are polymers of amino acid monomers
amino acids are lined by peptide bonds to form polypeptides
around 20 different amino acids
describe the peptide bond
a strong COVALENT bond between a carbon atom of one amino acid and the nitrogen atom of another amino acid. water is removed from between the two amino acids to allow the bond to form
What do amino acids contain
central carbon atom
hydrogen atom
amine group
carboxylic acid group
r group
Carch
what are the main categories the amino acids are split into (according to R group) are
polar
hydrophobic
acidic -ve
basic +ve
describe acidic R groups
ends with a negatively charged group
hydrophilic
keu component of their R group is a carboxyllic acid group COOH
descrivbe basic R groups
ends with a +ve charged group
hydrophilic
amine group
describe polar R group s
slightly chargeed
hydrophilic
carbonyl, hydroxyl, amine group
describe hydrophobic R groups
Hydrophobic
no charge
non-polar
hydrocarbon group- CH3 and rings
what are the different levels of protein structure
primary
secondary
tertiary
quaternary
describe the primary structure
the sequence on which the amino acids are synthesised into the polypeptide
describe secondary structure
hydrogen bonding along the backbone of the protein strand results in regions of secondary structure.
what are the three types of secondary structure
Alpha helix
beta sheets
turns
describe alpha helix
is formed by TWISTING the polypeptide chain into a spiral/helix and then stabilising with hydrogen bonding
the R groups sticks out
describe beta sheets
has parts of the chain running alongside each other forming a sheet
R groups sit above and below the sheet
they can be parallel or antiparallel
describe turns
they reverse the direction of the polypeptide chain and the chain folds back in on itself
describe tertiary structure
it is stabilised by many different interactions between R groups
whta are he several possible R group INTERACTIONS
hydrophobic
ionic
LDF
Hydrogen bonds
Disulfide bridges
describe hydrophobic reactions
tend to cluster together on the interior of a protein, away from the surface
describe ionic bonds
Occurs when atoms that are oppositely charged are held by an electrostatic attraction COOH and NH2 become COO- andNH3+ they are strongly charged and attracted to each other
describe LDF
weak interactions beween the electron clouds of atoms, these interactions may result in atraction or repulsion between atoms
describe Hydrogen bonds
weaker interactions between amino acids it is an electrostatic attraction which occurs between H +FON
describe disulfide bridges
covalent bond between R groups containing sulfur
describe quaternary structure
they exist in proteins with two or more connected polypeptide subunits which are linked by bonds between the r groups of the poly peptide chains
quaternary structure describes the spatial arrangement of the subunits
describe prosthetic groups +eg
a Prosthetic group is a non-protein unit tightly bound to a protein and necessary for its function
The ability of haemoglobin to bind oxygen is
dependent upon the non-protein haem group.
what can influence the interactions of the R groups
pH and temperature
how does increased temperature affect interactions of R groups
disrupts the interactions that hold the protein in shape.
the protein begins to unfold, becoming denatured
how does changing pH affect R group interactions
as pH moves from optimum, the normal ionic interactions between charged groups are lost, which gradually changes conformation of the protein until it becomes denatured
describe ligands
it is a substance that can bind to a protein
Ligand binding changes the conformation
of a protein and therefore causes a functional change in the protein
describe allosteric enzymes
an enzyme whose activity is regulated by altering its conformation
many have quaternary structure
contain a second site Allosteric site, this binds to something other than the substrate
describe modulators
they regulate the activity of enzyme when they bind to the allosteric site
after modulators conformation changes this alters the addinity of the active site for the substrate
what is the two types of modulators
negative and positive
negative modulators
reduce tje enzymes affinity for the substrate= decrease in activity
positive modulators
increase the enzymes affinity for the substrate = increase in activity
allosteric proteins with multiple subunits show what
co-operativity in binding, which changes in binding at one subunit after the affinity of the remaining subunits
give an example of cooperativiry
haemoglobin
made of four polypeptide subunits
each subunit contains haem group(binds oxygen)
when one of the sububits bind a molecule of oxygen subsequent binding by other subunits is more likely
when oxyhaemoglobin releases oxygen the same process happens
what influence does pH and temperature have on haemoglobin
lower the affinity of haemoglobin for oxygen, so the binding of oxygen is reduced
describe what happens when pH is reduced and temperature is increased in actively respiring tissue
reduce the binding of oxygen to haemoglobin promoting increased oxygen delivery to tissue
what is a common form of post-translational modification
phosphorylation , this is when a phosphate group is added to a protein
what can the addition or removal of phosphate cause
reversible conformational changes in proteins
describe protein kinases
catalyse the transfer of a phosphate group from ATP to other proteins.
the terminal phosphate of ATP is transferred to specific R groups
describe protein phosphatases
catalyse the transfer of a phosphate group from proteins onto ADP to regenerate ATP
how is many cellular proteins (enzymes and receptors) regulated
through phosphorylation as it causes conformational changes and therefore affecting activitywha
what does adding phosphate groups do to the charge
adds negative charge. ionic interactions in the unphosphorylated protein can be disrupted and new ones created
