Holiday homework/cell/protein synthesis Flashcards
What is exocytosis and its process?
- active movement of substances outside the cell in membrane-bound vesicles
- Vesicles form inside the cell from the RER, golgi apparatus, lysosomes and endosomes
- Vesicles containing newly synthesised proteins or waste products move towards the plasma membrane
- plasma membrane and vesicular membrane fuse together
- contents of vesicle expelled into extracellular fluid
What are cells?
- the basic structural and functional unit of life
Why do cells need to be small?
- maximise their surface area to volume ration to efficiently move ions, nutrients and waste
Prokaryotes vs eukaryotes: unicellular/multicellular
Prokaryotes: bacteria and archaea
- lack membrane boune nucleus
- unicellular
- no cytoskeleton
- chemicallu complex cell wall
Eukaryotes: animals, plants, chromista, fungi, protozoa,
- mostly mutlicellular (can be unicellular)
- sometimes cell wall but chemically simple
Importance of compartmentalisation in eukaryotic cells:
- efficiency
- creates specific microenvironments (e.g. pH, ion concentration) within the cell so each organelle can have the advantages it needs to perform to the best of its ability
Location of nucleolus and what it does
- within nucleus
- ribosomal subunits are synthesised
Where can ribosomes be found and what is their role?
- free in cytosol or attached to RER
- role is protein synthesis
- small subunit reads mRNA and large subunit joins amino acids which are connected via peptide bonds to form polypeptide chains
what do the endoplasmic reticulums look like?
- interconnected network of flattened membrane-enclosed channels
- continuous with outer nuclear membrane
Role of smooth ER
- synthesise lipids
- metabolism of carbohydrates
- calcium storage
- detoxification of drugs and poisons
Role of rough ER and what happens to proteins there
- processes proteins from ribosomes
- attaches carbohydrate groups to some proteins to form glycoproteins
- folds proteins into correct functional shape
- joins together several popypeptide chains to form complex proteins
Golgi apparatus appearance and function
- mutli layered structure composed of stacks of membrane-lined channels with wider ends
- modifies, sorts, packages and distributes proteins into secretory vesicles
Lysosomes
- membrane bound sac
- contain hydrolytic enzymes
- found only in animal cells
- contains digestive enzymes
- breaks down material taken into the cell and obsolete components of the cell itself
Vacuoles
- large membrane bound sacs
- found in plant cells (one, large) and some animal (smaller, multiple)
- store water
- isolate harmful materials to cells
- store waste products
- maintain internal turgor pressure (plant cells- force that pushes cell membrane against cell wall)
peroxisomes
- eukaryotic cells
- act as recycling centre of the cell, breaking down harmful substances
- involved in oxidation of molecules (e.g., amino acids, fatty acids), where electrons are lost.
- Produce hydrogen peroxide (H₂O₂) as a byproduct of oxidation.
Contain the enzyme catalase, which converts hydrogen peroxide into water and oxygen. - break down very long fatty acid chains through beta oxidation
- metabolism of other substances (e.g. lipids, amino acids)
mitochondria and role in protein synthesis and secretion
- double membrane
- inner membrane has series of folds (cristae) containing enzymes for ATP synthesis
- matrix is fluid-filled space within inner membrane
- provide energy in form of ATP for translation/synthesis of protein, for packaging proteins into vesicles
Plasma membrane
- semi permeable
- controls the entry and exit of materials into and out of cells
Functions:
- is an active and selective boundary (separates cell from external environment)
- denotes cell identity (vital for immune response)
- receives external signals
- transports materials.
Factors that affect a substance’s ability to cross a membrane
Molecules that can pass easily through the cell membrane:
* small polar molecules such as water
* non-polar molecules such as carbon dioxide.
Molecules that cannot pass easily through a membrane:
* large polar molecules such as glucose (polar molecules are neutral because the uneven charges balance out)
* charged molecules (ions)
Simple diffusion
the movement of solute particles across a semi-permeable membrane from a region of high concentration to a region of low concentration to reach equilibrium
- small polar molecules
- non-polar (lipophilic/hydrophobic)
Facilitated diffusion
net passive movement of polar or charged molecules from an area of high to low concentration with the aid of proteins such as carrier or channel proteins.
- large polar and charged molecules, water (aquaporins)
Active transport
The net active movement of particles that requires energy in the form of ATP from an area of low to high concentration with the aid of transport proteins such as carrier proteins.
- hydrophyllic substances
Bulk transport
- active transport
- too large for carrier proteins
- high to low concentration??
Endocytosis:
- enter cell
- phagocytosis (solid)
- pinocytosis (liquid)
1. substance approaches plasma membrane
2. Portion of plasma membrane is invaginated
3. membrane forms vesicle that contains substance
Exocytosis:
- substance encolsed in a vesicle from the golgi apparatus
- vesicle fuses with plasma membrane and releases contents
Osmosis
a specialised process of
passive transport in which water
molecules move across a partially
permeable membrane from an area
of high water (low solute) to an area
of low water (high solute)
structure of membrane (proteins, cholesterol, temp, carbs)
- double layer of phospholipids
(hydrophilic heads on outside, hydrophobic tails face each other) - integral proteins (embedded in membrane, transmembrane proteins span entire width)
- peripheral proteins (anchored to exterior of plasma membrane
through bonding with lipids, or indirectly associated with plasma membrane through interactions with integral proteins) - cholestoral (animal cells only):
at low temps, maintains fluidity by keeping phospholipids separated and keeping it from becoming too stiff
-at high temps, stabilizes membrane by restricting movement of phosopholipids, reduces permeability to some small water-soluble molecules from becoming too fluid thus raising melting point
- carbohydrates: attached to lipids (glycolipid), attached to proteins (glycoproteins) (peripheral)
cell to cell communication, receptors and recognition
How to describe structure of plasma membrane
- fluid mosaic model
- phospholipids can move laterally (influenced by unsaturated fatty acids- kinks in the tail that make it more fluid)
- looks like a mosaic with proteins embedded
Phospholipids
- two fatty acid chains (non polar/hydrophobic)
- joined to phosphate containing group (hyrdophilic/polar)
Proteins in membrane
Integral proteins:
permanent parts of cell membrane
Transmembrane proteins:
span both phospholipid bilayers
Peripheral proteins:
- temporary
- surface of membrane
Coded vs decoded information
Coded information: nucleotide sequences in DNA template strand
Decoded information: order of amino acids in a polypeptide (decoding is transcribing and translating sequences into proteins)
why is the genetic code referred to a triplet code?
the idea that the
genetic code consists of triplets
or three-base sequences
what is the strand of a DNA
double helix that is complementary
to the template strand
the coding strand, non-template strand
what is pre-mRNA also known as?
the primary transcript
what is tRNA made out of?
- single strand of 76 nucleotides coiled and paired with themselves
- anticodon
- region that attaches to one specific amino acid
- amino acyl tRNA synthetase catalyses linking of amino acid with tRNA
what are the advantages and disadvantages of the universability of the genetic code in humans?
Advantages:
- gene manipulation and therapeutic uses: can insert human genes into any other organism such as bacteria and they can express the same proteins as in humans.
e.g. insulin
- more easily sequence genes of other species and determine the proteins that will be produced
Disadvantage:
- easier for foreign dna to be incorporated into a genome. e.g. some viruses can hide in the genomes of host cells without being recognised as foreign
A change in the DNA sequence that does not result in a change in the amino acid sequence is known as a ??? mutation.
silent
What would be the consequence if the fifth-last base in the sequence mutated from adenine to thymine, changing the stop protein to another amino acid?
It would change the length of the polypeptide, possibly chaning structure and function of the protein.
how many amino acids can humans not make?
9 (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.)
What are catalysts?
substances that speed up the rate of chemical reactions
function of enzymes
increase the rate of chemical reactions in cells within the cell’s prevailing temperature and pH conditions
bind to substrate, lower the activation energy
without enzymes, speed of biochemical reactions would be too slow to sustain living state
are all enzymes proteins?
exception: ribozymes- are catalytic RNA molecules that can cut themselves
out of long RNA sequences.
what is the proteome?
complete array of proteins produced by a single cell or organism in a particular environment
What are the types of proteins?
Structural- fibrous support tissue (keratin, collagen)
enzyme- catalyse reactions (ATP synthase)
contractile- muscle movement (myosin, actin)
Immunoglobulin- defence against disease (antibodies)
Hormone- regulate body activity (insulin)
Receptor- responds to stimuli (insulin receptors)
Transport- carry other molecules (haemoglobin)
Conjugated- consists also of non-protein elements called prosthetic groups (e.g. haemoglobin which contains protein chains linked to haem groups)
What are some advantages of studying the proteome over the genome?
- proteome is more complex: better understanding of organism, see expression of genes and when genes are inactive/active
- better understanding of post transcriptional and post translational modifications (understand removal of introns, alternative splicing and how it affects function of protein)
- explore interaction between different proteins and proteins do not act in isolation
An individual has a deficiency in an enzyme that catalyses the breakdown of lactose.
a. What are the possible consequences of this?
b. With reference to genes and proteins, explain how this may occur.
a - cannot properly digest or break down lactose (the chemical reaction will occur far too slowly).
- may cause illness.
b - mutation in the gene coded for
lactase
- leads to a different protein being transcribed (or even no protein being
transcribed at all), causing a non-functional lactase enyzyme to be formed.
Explain why beta-pleated sheets may be important in the function of a particular protein.
- Structure of proteins allow them to elongate or contract
- provides strength and stability (due to hydrogen bonds)
- provides an active site for enzymes or other molecules
Proteins can also be classified on the basis of their general function. Three of these functions are listed below.
* structural
* transport
* regulatory
Give an example of a protein for each of the functions listed.
structural:
keratin, collagen, silk, cilia, cytoskeleton
transport:
haemoglobin, serem albumin, protein carrier
regulatory:
OR lacl (lactose repressor)
some hormones (e.g insulin) , some enzymes (e.g kinases), (transcription factors I think) major histocompatibility complex
what are ribosomes made up of?
- strands of rRNA merged with about 80 ribosomal proteins (r-proteins).
Where is the RNA of ribosomes made?
- rRNA is made in the nucleolus
- mRNA is made in the nucleus
- trna in nucleus
true or false: The folding of a protein into its functional 3D shape takes place on the ribosomes.
folding of a proteins detined for secretion takes place on the rough endoplasmic reticulum
Does trna contain thymine or uracil?
uracil
What is gene regulation?
Gene regulation are the mechanisms used to express genes only when they are required, thus conserving energy.
Describe two advantages of an operon over an unregulated gene structure.
- Genes are transcribed only when they need to be
- energy efficient- amino acids and ATP aren’t unnecessarily used
- prevents toxic buildup of proteins and enzymes
When testing a hypothesis, it is important to include a control group in the experiment because this
helps to ensure that the results can be compared to a standard
Refer to the following table, which shows the surface area to volume ratio of a plant cell at two stages of its growth.
Stage of growth
Surface area to volume ratio
W
3:1
X
1:1
At stage W of its growth, the plant cell Plant cell
a. is of a smaller size than at stage X
b. is less efficient in exchanging materials by diffusion than at stage X
c. has a larger surface area than at stage X
d. has a larger volume than at stage X
A
A higher surface area to volume (SA:V) ratio, such as 3:1, typically indicates a smaller cell size compared to a lower SA:V ratio like 1:1. This is because smaller cells have a relatively larger surface area compared to their volume.
not c because:
Although the surface area to volume ratio is higher at stage W, the actual surface area is smaller because the cell is smaller in size.
what is ligase?
- enzyme that catalyzes the joining or ligation of two strands of DNA.
- creates a phosphodiester bond between the sugar-phosphate backbones of adjacent nucleotides in DNA. - - crucial for DNA replication, repair, and recombination.
what is the role of collagen?
Keratin?
Collagen: provides structural support to the extracellular space of connective tissues.
keratin: serves as a protective layer in the skin
what are the stop codons?
UAA, UAG and UGA (on mRNA)
TAA, TAG, TGA (on coding strand)
