BRAMPTON ANKI EXAM QUESTIONS Flashcards
Describe the structure of proteins [6 marks]
> Polymer of amino acids
Joined by peptide bonds
That are formed by condensation
> Primary structure is the sequence/order of amino acids
> Secondary structure is folding of polypeptide chain due to hydrogen bonding - forms alpha helixes / beta pleated sheets.
> Tertiary is 3D folding due to hydrogen, ionic and disulfide bonds.
> Quaternary structure is 2 or more polypeptide chains.
Describe the structure and function of cellulose [6 marks]
1) Polymer of β-glucose.
2) Joined by condensation to form 1,4 glycosidic bonds
3) …so straight-chain, unbranched structure.
4) Alternate glucose molecules are rotated 180° (“flipping over”)
5) Hydrogen bonding crosslinks between adjacent chains…
6) …so it forms microfibrils for high tensile strength.
7) A structural unit making cell walls strong as it provides rigidity…
8) …so it can resist osmotic pressure
9) Bonds difficult to break
10) Resists action of enzymes
ATP is useful in many biological processes. Explain why [4 marks]
1) Releases energy in small, easily manageable amounts.
2) Broken down in a 1 step reaction so energy is available rapidly.
3) Phosphorylates substances to make them more reactive
4) Reformed/made/resynthesised again rapidly.
Describe the biochemical tests you would use to confirm the presence of lipid, non0reducing sugar and amylase in a sample [5 marks]
= LIPID =
1) Add ethanol and shake then add water and shake gently
2) White/milky emulsion
= NON-REDUCING SUGAR =
1) Do Benedict’s test and stays blue/negative
2) Boil with acid then neutralise with alkali
3) Heat with Benedict’s and forms red/orange precipitate
= AMYLASE =
1) Add biuret reagent and becomes purple.
2) Add starch, (leave for a time), test for reducing sugar OR absence of starch.
Explain 5 properties that make water important for organisms [5 marks]
1) A METABOLITE in condensation/hydrolysis/photosynthesis/respiration.
2) A SOLVENT so metabolic reactions can occur.
3) High HEAT CAPACITY so buffers change in temperature.
4) Large LATENT HEAT OF VAPORISATION so provides a cooling effect (through evaporation)
5) COHESION between water molecules, so supports columns of water (in plants)
6) OR produces surface tension supporting small organisms.
Explain how the structure of DNA is related to its functions [6 marks]
1) Double helix structure w/ many H bonds =
> Provides stability to molecule.
2) Coiling =
> Makes DNA compact - stores lots of info in a small space.
3) Long molecule =
> Stores a large amount of info.
4) Strong covalent sugar-phosphate backbone =
> Gives strength - prevents code from being corrupted.
5) H bonds between bases are weak =
> Allows chains to split easily for replication and transcription.
6) Sequence of bases =
> Allows info to be stored.
Describe and explain how the structure of DNA results in accurate replication [4 marks]
1) Forms TWO strands therefore semi-conservative replication.
2) Base pairing held together by hydrogen bonds.
3) Hydrogen bonds weak so easily broken, allowing strands to separate.
4) Bases exposed and act as a template
5) A with T, C with G
6) DNA made has 1 parent strand and 1 new strand.
Explain how a mutation can result in the production of a non-functional protein receptor [4 marks]
1) Change in DNA base sequence
2) Change in amino acid sequence
3) This alters position of hydrogen/ionic/disulfide bonds
4) And causes a change in the tertiary structure (of receptor)
State the formula for pH [1 mark]
pH = -log10[H+]
Give the properties of glycogen [4 marks]
1) Insoluble ⟶ doesn’t affect water potential
2) Large ⟶ cannot leave cells
3) Compact ⟶ more energy stored in small spaces
4) Highly branched ⟶ larger surface area for enzymes to act on
Explain why maltase can only catalyse the hydrolysis of maltose [3 marks]
1) Active site of enzyme has specific shape
2) Only maltose can bind
3) To form ES complex
Compare and contrast the structure and properties of triglycerides and phospholipids [9 marks]
SIMILARITIES =
> Both contain ester bonds
> Both contain glycerol
> Both insoluble in water
> Both contain C, H, O
DIFFERENCES =
> Phospholipids contain phosphate group
> Triglycerides have 3 FA chains, phospholipids have 2 FA chains + phosphate group.
> Triglycerides are hydrophobic/non-polar, whereas phospholipids have hydrophobic & hydrophilic regions
> Phospholipids form bilayer in water
What is a monomer? [1 mark] MS
A repeating unit from with larger molecules are made
Describe how the structure of starch is related to its function [4 marks] MS
1) Helical/spiral shape so compact
2) Molecule is insoluble so doesn’t affect WP.
3) Branched so glucose is easily accessible by enzymes to break down for respiration
4) Large molecule so cannot leave cell
When investigating the effect of enzyme concentration on a reaction, what factors must we keep constant [3 marks]
1) Temperature of the solution
2) pH of the solution
3) Concentration of substrate
Describe how a peptide bond is formed between 2 amino acids to form a dipeptide [2 marks]
1) Condensation reaction
2) Between amine and carboxyl group
Describe how the secondary structure of a polypeptide is produced by bonds between amino acids [2 marks]
1) Hydrogen bonds
2) Between NH and C=O
Describe the function of DNA helicase [1 mark]
1) Unwinds DNA
2) Breaks hydrogen bonds between strands
Describe the function of DNA polymerase [1 mark]
1) Joins nucleotides
2) Forms phosphodiester bonds
Contrast the structures of ATP and a nucleotide found in DNA [3 marks]
> ATP has ribose whereas DNA nucleotide has deoxyribose
> ATP has 3 Pi whereas DNA has 1 Pi
> ATP always has base adenine, whereas DNA nucleotide can vary
Describe 4 differences between the structure of a cellulose molecule and a glycogen molecule [4 marks]
> alpha VS beta
> branched VS straight-chain
> coiled VS straight-chain / microfibrils
> 1,4 & 1,6 glycosidic bonds VS only 1,4 glycosidic bonds
Describe the structure of glycogen [3 marks]
1) Polysaccharide of alpha glucose
2) Joined by glycosidic bonds
3) Branched structure
Suggest how glycogen acts as a source of energy [2 marks]
1) Hydrolysed to form glucose
2) Glucose used in respiration
Compare and contrast the processes by which water and inorganic ions enter cells [3 marks]
> Both move down concentration gradient
> Both move through protein channels in membrane
> Ions can move against a concentration gradient by active transport
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein [4 marks]
1) Glucose and galactose
2) Joined by condensation
3) Joined by glycosidic bonds
4) Added to polypeptide in GOLGI apparatus
Give 2 ways om which the nucleotides in DNA are different from the nucleotides in RNA [2 marks]
> DNA ⟶ deoxyribose sugar
RNA ⟶ ribose sugar
> DNA ⟶ contains thymine
RNA ⟶ contains uracil
> DNA ⟶ long polymer chain
RNA ⟶ short polymer chain
> DNA ⟶ 2 helical strands
RNA ⟶ single strand
Draw the structure of ATP [1 mark]
From LEFT to RIGHT…
Rectangle = adenine
Pentagon = ribose sugar
3 circles = phosphate groups
Explain how the organic bases help to stabilise the structure of DNA [2 marks]
1) Hydrogen bonds between the base pairs holds 2 strands together
2) Many hydrogen bonds provide strength
Describe how you can investigate the permeability of a cell membrane in the lab using beetroot: [6 marks]
1) Cut 5 equal sized pieces of beetroot using a scalpel
2) Rinse to remove pigment on the surface after cutting
3) Add each piece to a test tube with 5 cm3 of water
4) Place each in a different temperature water bath (10, 20, 30, 40 and 50 ºC) for the same amount of time
5) Remove the beetroot so only coloured liquid is left
6) Determine the absorption of the coloured solution left using a colorimeter
7) High absorbance means more pigment was released
8) Plot on a graph, or connect the colorimeter to a computer
Mitosis is important in the life of an organism. State reasons why. [4] MS
- Growth / increase in cell number;
- Replace cells / repair tissue / organs / body;
- Genetically identical cells;
- Asexual reproduction / cloning;
Discuss the advantages and disadvantages of using a transmission electron microscope. [4 marks]
ADVANTAGES =
> Best magnification and resolution
> Allows internal structures to be seen
DISADVANTAGES =
> Can’t look at living cells → specimen need to be in a vacuum
> Specimen must be very thin
> Artefacts present
> Long preparation time and complex staining process
> Doesn’t form a colour image
> Only 2D images produced
State the adaptations of the plasma membrane for its functions [6 marks]
1) Phospholipid bilayer forms a barrier (to water soluble substances)
2) Fluid ⟶
can bend to take up different shapes E.G. to form vesicles / self repair
3) Channel proteins ⟶
let water soluble/charged particles substances through
4) Carrier proteins ⟶
allow for facilitated diffusion
5) Surface proteins / Glycoproteins ⟶
act as receptors
6) Cholesterol ⟶
regulates fluidity
Describe how substances move across cell surface membranes by facilitated diffusion MS [3 marks]
1) Carrier / Channel Protein
2) Protein’s are specific to substance
3) Substance moves down the concentration gradient
Explain how epithelial cells absorb glucose via co-transport with sodium ions. MS [3]
1) Sodium ions actively transported from the ileum cell to blood
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2) This maintains the concentration gradient for sodium to enter from gut, each coupled with a glucose molecule
3) Glucose enters by facilitated diffusion via a co-transport protein with sodium ions
How would the addition of a respiratory inhibitor stop the absorption of amino acids in the ileum? MS [4 marks]
1) No ATP produced
2) Sodium ions not moved out of the cell
3) No concentration gradient for sodium to move into the cell with amino acids, hence no amino acids are absorbed
Describe how bacteria divide [4 marks]
> Binary fission
Replication of circular DNA
Division of cytoplasm to produce 2 daughter cells
Each with a single copy of circular DNA
Describe the roles of centromeres [3 marks]
> Holds chromatids together
Attaches chromatids to spindle
Allows chromatids to move to opposite poles
Give 4 reasons why mitosis is important in the life of an organism. [4 marks]
> Growth in cell number
Replace cells
Genetically identical cells
Asexual reproduction
What is an antigen? MS [2 marks]
FOREIGN protein;
that STIMULATES an immune response
Explain why cancer treatments based on immunological methods
are more likely to minimise damage to healthy tissue [5 marks]
> Proteins on cell surface membrane of cancer cells;
different from healthy cells (abnormal);
abnormal cell surface proteins are non-self antigens;
immunotherapy facilitates immune system by detecting non-self-proteins;
immune system mounts immune response; destroys cancer cells
Cancer is often described as the result of the cell cycle “being out of control”. Explain this statement.
Cell cycle describes the formation of new cells from old cells
Checkpoints regulate the progression of the cell replication
Genes control these checkpoints
Mutation of genes
Control is lost
Cancer develops / uncontrolled cell cycle/mitosis
Explain why the antibody will only detect this antigen. [3 marks]
1) Antibody has a variable region with a specific amino acid sequence / primary structure;
2) The shape of tertiary structure of the binding site;
3) Complementary to the antigens;
4) Forms complex between antigen and antibody;
Explain why an electron microscope shows more detail of cell structure than a light microscope [2 marks]
1) Electron microscope has a greater resolving power / objects closer together can be distinguished
2) electron (beams) have a shorter wavelength;
What are the functions of glycoproteins? [2 marks]
> Act as recognition sites
> Help cells attach to one another + form tissues
What are lysosomes and their function? [2 marks]
> Membrane-bound vesicles found in the cytoplasm that contain a hydrolytic enzyme called lysozyme.
> They are responsible for digesting invading cells / breaking down work out components
Recall the structure of chloroplasts [6 marks]
1) Small, flattened structure found within plant and algae cells
2) Contains a double membrane
3) Stroma is an aqueous liquid found within these membranes (contains enzymes)
4) Contains structures within called thylakoids
5) Stacked thylakoids = grana
6) Grana linked to each other by thin, flat piece of membrane called a lamellae
7) Contains circular DNA and ribosomes
How are SEM images created?
e- beam is directed from above
e- beams are scattered which are analysed by a computer to build a 3-D image.
Describe a method to quantify the amount of sugar in a solution without a colorimeter MS [3]
1) Filter
2) Dry precipitate
3) Find mass / weight
What is a monoclonal antibody? MS [2]
1.Antibodies with the same tertiary structure
2. produced from identical plasma cells
How are photomicrographs formed using a TEM?
e- gun produces a beam of e- -> focused on specimen by electromagnet.
beam passes through specimen, denser areas are absorbed causing dark spots.
What do prokaryotic cells have instead of Mitochondria?
Mesosomes
These are in foldings of the cell membrane that provide a large surface area for the attachment of the enzymes involved in respiration.
Outline the steps in preparing a ‘‘temporary mount’’
1) Start by pipetting a small drop of water onto the slide
2) Use tweezers to place a thin section on top of the water drop
3) Add a drop of stain E.G. eosin to make cytoplasm show up
4) Use a mounted needle to add a cover slip to protect the specimen. Try and avoid air bubbles.
Describe the function of cholesterol in the cell membrane [3 marks]
Cholestrol regulates the fluidity of the cell-surface membrane.
Key Functions:
- reduces lateral movement of other molecules including phospholipids
- makes the membrane less fluid at high temperatures
- prevent leakage of water and dissolved ions from the cell as it is hydrophobic
What is the main difference between fungal cells and plant cells?
Fungal cells are like plant cells, except:
> Cell walls are made of chitin, instead of cellulose
They don’t have chloroplasts
Which extra organelles do plant cells have compared to animal cells?
A cellulose cell wall
A vacuole full of cell sap
Chloroplasts
What is a mitochondrion, and what is its function?
STRUCTURE =
> Oval shaped
> Double membrane
> Inner membranes are folded to form cristae
> Has a matrix inside - this contains enzymes involved in respiration
FUNCTION =
> Site of aerobic respiration
> ATP produced here
> Found in large numbers in active cells that have high energy requirements
What is a golgi apparatus, and what is its function?
> A group of fluid-filled membrane bound flattened sacs
Processes and packages new lipids and proteins
Makes lysosomes
What is a Golgi vesicle and what is its role?
A small fluid filled sac
Surrounded by a membrane
Made by the Golgi apparatus
Stores lipids and proteins that are made by the Golgi apparatus
Transports them out of the cell by the cell surface membrane during exocytosis
What is a ribosome, and what is its structure/function?
> Site for protein synthesis
> Floats free in the cytoplasm or attached to the rough endoplasmic reticulum
> Made of proteins and rRNA
What is a smooth endoplasmic reticulum (SER), and what is its function?
Network of fluid-filled membranes
Produces and processes lipids
What is a cell wall, and what is its function?
1) Rigid cellulose structure that surrounds plants
2) Provides structural support to the plant and therefore keeps it rigid
What is a vacuole, and what is its function?
An organelle found enclosed by a membrane (tonoplast)
In the cytoplasm of plant cells
Contains sap - a weak solution of salts and sugar
Helps maintain cell pressure, ensuring the cell remains rigid and prevents wilting of the plant
Isolates and detoxifies unwanted chemicals in the cell
Why may cells have lots of mitochondria?
If the cell used lots of energy
Why do some cells have villi?
This increases the surface area for absorption
e.g. in the epithelial cells of the small intestine
What is a group of cells called?
tissue
What is a tissue?
A group of (specialised) cells that works together to carry out a specific function
What are organs?
Groups of different tissue that work together to perform certain functions
What is an organ system?
A group of organs that works together to perform a function in a multicellular organism
Describe the structure and function of the cell wall of prokaryotic cells:
> Retains the structure of the cell, prevents it from changing shape
Made of murein polymer
Murein is a glycoprotein
Describe the plasmids found in prokaryotic cells:
> Small loops of DNA
Contain antibiotic resistance genes amongst others
Some have several plasmids, others have no plasmids
Describe the DNA of prokaryotic cells: [4 marks]
1) No nucleus is present
2) DNA is free in the cytoplasm
3) Circular DNA
4) Not attached to any histone proteins
Viruses have no…
No plasma membrane
No ribosomes
No cytoplasm
How do prokaryotic cells replicate?
By binary fission
Cells split to make two daughter cells
What is magnification and how is it calculated?
How much bigger the image is than the actual sample/specimen
Magnification = size of image / size of object
What is resolution?
How well can a microscope distinguish between two points that are close together
Compare SEMs and TEMs:
> SEMs can be used on thick specimens, TEMs can only be used on thin specimens
SEMs give lower resolution images than TEMs
SEMs produce 3D images
What is cell fractionation?
The separation of organelles from the rest of the cell, before examining them under an electron microscope
What are the three stages of cell fractionation?
Homogenisation - Breaking cells
Filtration - Removing large debris
Ultracentrifugation - Separating the organelles
Contrast the structure of a bacterial cell and the structure of a human cell. [6 marks]
1) Bacterial is much smaller than human
2) Bacterial has cell wall but human doesn’t
3) Bacterial lacks nucleus but human has nucleus
4) Bacterial lacks membrane-bound organelles but human has membrane-bound organelles
5) Bacterial have 70S ribosomes whereas human have 80S ribosomes
6) Bacterial DNA is circular but human DNA is linear
7) Bacterial DNA is ‘naked’ whereas human DNA is bound to histones
Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells. [6 marks] MS
1) Cell homogenisation to break cells open
2) Filter to remove large debris
3) Use isotonic solution to prevent damage to mitochondria
4) Keep cold to prevent damage by enzyme
5) Use buffer to prevent protein denaturation
6) Centrifuge at lower speed to separate nuclei
7) Re-spin supernatant at higher speed to get mitochondria in pellet at bottom
What are the two main stains we use during microscopy?
Eosin is used to highlight the cytoplasm
Iodine contained in potassium iodide solution highlights starch grains
Bacterial cells have ____ ribosomes whereas human cells have ____ ribosomes
Bacterial cells have 70S ribosomes whereas human cells have 80S ribosomes
Why do electron microscopes have a higher resolution than optical microscopes?
Electrons have a shorter wavelength.
Define introns and describe where they are positioned in the genome MS [2 marks]
1) DNA that does not code for amino acids
2) Positioned between genes
Describe the induced fit model of enzyme action. MS [3 marks]
Active site of enzyme is not complementary;
Active site is flexible & can mould around the substrate;
change in enzyme allows substrate to fit and form an E-S complex
Explain why maltase:
* only breaks down maltose
* allows this reaction to take place at normal body temperature. [5 marks]
- Specific Tertiary structure enzyme (means)
- Active site is only complementary to maltose
- Description of induced fit;
- Enzyme is a catalyst which lowers the activation energy required for the reaction
- By forming an enzyme-substrate complex;
Why is ATP needed?
Energy can’t be directly released from glucose
Energy released from glucose makes ATP
What is ATP?
The nucleotide tide base is adenine
The pentose sugar is called ribose
There are three phosphate groups
A modified nucleotide, known as a nucleotide derivative
Energy is stored in bonds between phosphate groups, and released by hydrolysis reactions
How is energy released from ATP?
ATP is broken down under a hydrolysis reaction
Broken down into ADP (adenine diphosphate) and Pi (inorganic phosphate)
The phosphate bonds are broken, and energy is released
This is catalysed by ATP hydrolase, an enzyme
Describe the structure of a virus:
Contain core genetic material, as RNA or DNA
Have a ‘capsid’ which is a protein coat
Attachment proteins stick out from the edge of the capsid to allow the virus to attach to a host cell
How is the inorganic phosphate (Pi) released from the hydrolysis of ATP used?
Added to another compound by phosphorylation
This makes the compound more reactive
How can ATP be resynthesised?
A condensation reaction
Between ADP and Pi
This occurs during respiration and photosynthesis
Catalysed by ATP synthase
ATP is useful in many biological processes. Explain why MS [4 marks]
1) Releases energy in small / manageable amounts
2) Broken down in a one step reaction
3) Phosphorylates other compounds to make them more reactive
4) Reformed / remade / easily resynthesised
Write a simple equation to show how ATP is synthesised from ADP: MS [1 mark]
ADP + Pi → ATP
Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP: MS [2 marks]
ATP cannot be stored it is an immediate source of energy
Only a small amount of energy is released at a time
Describe how ATP is resynthesised in cells. [3 marks]
From ADP and Pi
By ATP synthase
During respiration/photosynthesis
Where does the energy in ATP come from?
The unstable bonds between the phosphate molecules
