Progress Test (lectures 2-14) Flashcards
State the 8 characteristics of life
Cellular organisation Reproduction Metabolism Homeostasis Heredity Response to stimuli Growth and development Adaptation through evolution
How many micrometers in a metre?
1 million
Which take up most of the total distribution of organisms- plants or animals? How many Gt?
Plants- 450Gt
Humans- 0.7Gt
Natural selection
The process by which organisms better adapted to their environment survive and produce more offspring, leading to evolution of the species.
What is the process that allows for evolution?
Natural selection
Does natural selection act on biological molecules, or just animals and plants?
All
What does natural selection require? (4)
Variation
Inheritance
Selection
Time
Name of the diagram used to relate organisms to others through shared characteristics
Phylogenetic tree
Three domains of life
Archaea
Bacteria
Eukarya
Which domain can grow at very high temperatures?
Archaea- can grow at over 100 degrees Celsius
What term can be used to refer to both bacteria and archaea domains collectively?
Prokaryotes
Three main differences between prokaryotic and eukaryotic cells
Prokaryotic cells are smaller, have no nucleus and don’t contain organelles
Endosymbiosis
The theory which explains how eukaryotic cells may have evolved from prokaryotic cells.
Which organelles of plant and animal cells are derived from bacteria? What is the name of the theory that explains this?
Mitochondria and chloroplasts
Endosymbiosis
How much of a typical cell is water?
70%
Does DNA make up a large amount of the cell?
No- only 0.25%
What are the building blocks of the cell? (6)
Amino acids
Nucleobases
Simple carbohydrates
Glycerol, fatty acids, hydrocarbon rings
Macromolecules of the cell (5)
Proteins DNA RNA Complex carbohydrates Lipids
Which building block makes up proteins?
Amino acids
Which building block makes up DNA and RNA?
Nucleobases
Which building block makes up complex carbohydrates?
Simple carbohydrates
Which building blocks make up lipids? (3)
Glycerol, fatty acids, hydrocarbon rings
What are the three supramolecular assemblies of the cell?
Membranes
Ribosomes
Chromatin
Name the organelles found in an animal cell (5)
Nucleus Golgi apparatus Mitochondrion Endoplasmic reticulum Lysosomes
What organelle do plant cells contain that animal cells don’t?
Chloroplasts
Macromolecule
An organic biological molecule of large molecular mass which is necessary for life
Name the four levels of carbohydrate
Monosaccharides
Disaccharides
Oligosaccharides
Polysaccharides
Monosaccharides and disaccharides are what type of carbohydrate?
Simple
Oligosaccharides and polysaccharides are what type of carbohydrate?
Complex
How many sugars are in a monosaccharide?
One
Glucose is what type of carbohydrate?
Monosaccharide (simple)
Which monosaccharides are the building blocks of higher order carbohydrates?
Hexose monosaccharides
Which simple carbohydrates are usually part of larger molecules? Give an example of these molecules
Pentose monosaccharides, DNA
How are disaccharides made up?
By two monosaccharides joined together
How many monosaccharides join to form an oligosaccharide?
3-10
What is the name of the complex carbohydrate which is formed by joining over 10 monosaccharides?
Polysaccharides
Name two types of polysaccharides
Starch and cellulose
Describe starch
A plant carbohydrate made of long chains of glucose monomers linked to form a branch shape
Describe cellulose structure
A fibre- long chains of glucose stacked on top of each other
Functions of carbohydrates (3)
Recognition of other cells/ bacteria
Source of energy
Structure
What do nucleic acids do?
They are informational molecules- they tell the cell what to do and where and when to do it
Name the two types of nucleic acids
Ribonucleic acid RNA
Deoxyribonucleic acid DNA
What are the two structural differences between RNA and DNA?
DNA has a hydrogen atom whereas RNA has a hydroxyl group at the second carbon position
RNA has one polynucleotide, DNA has two
Name the three components of a nucleotide
Phosphate group
Ribose sugar
Base
Name the five bases in nucleic acids
Adenine
Guanine
Thymine/ uracil in RNA
Cytosine
What do bases A and G have in common?
They are both purines
Thymine, uracil and cytosine are all what type of base?
Pyrimidines
How do nucleotides join to form a polynucleotide?
They join by their phosphate groups
Transcription (cellular process)
Process by which DNA is copied to messenger RNA (mRNA)
Translation (cellular process)
Process by which mRNA is used to produce proteins
How do amino acids differ?
By their R group (side chain)
What base joins to cytosine?
Guanine
Which base joins to adenine?
Thymine
Which macromolecule is not a polymer?
Lipids
Name five common types of lipids
Triacylglycerols TAG (fats) Steroids Phospholipids Glycolipids Fat soluble vitamins
Are lipids hydrophilic or hydrophobic?
Hydrophobic
Three functions of lipids
Forming cell membrane
Energy storage (in form of fat molecules TAG)
Regulate temperature
Five actions of the cell
Manufacture cell materials Obtain raw materials Remove waste Generate required energy Control above actions
Why does the cell have separate organelles? (3)
To provide different conditions for specific processes
To allow substances to be concentrated, and therefore form concentration gradients
To package substances for transport
What is the name of the semi-permeable barrier at the boundary of the cell? What does this semi-permeability mean?
Plasma membrane
It controls what substances are let in and out
Which parts of a phospholipid bilayer are hydrophobic/phillic?
Hydrophobic head
Hydrophilic tails
What are the hydrophobic tails of phospholipids made of? What do they do?
Fatty acids, affect membrane fluidity.
Describe a more fluid phospholipid bilayer
The tails (fatty acids) are unsaturated, so they prevent packing. This is due to the kinks in the tails caused by double bonded carbons.
Describe a more viscous phospholipid bilayer
Saturated tails are packed tightly together.
What is the function of cholesterol in cell membranes? Which cells is it found in?
It fits between phospholipids and strengthens and stabilises the membrane. Found only in animal cells
Name the three types of transport across the cell membrane
Passive, active and co-
What is the difference between diffusion and facilitated diffusion?
Hydrophobic molecules are able to pass through the membrane- diffusion.
Hydrophilic (including charged) molecules are able to pass through the membrane using channels and carriers- facilitated diffusion.
Difference between passive and active transport
Molecules move down their concentration gradient in passive transport, and against it in active transport.
Aquaporins
Channel proteins which allow water molecules to move down their concentration (osmotic) gradients
Is active transport aiming for homeostasis?
No, it moves molecules against their concentration gradients.
What is needed for active transport to take place? (2)
Energy, usually in the form of ATP
Transport proteins to facilitate the movement
Contransport
A form of active transport that allows two or more types of molecules to cross the membrane against their concentration gradients.
Example of contransport
H+ ions are pumped out of cell by proton pump
They cross back into it passively, taking sucrose molecules with them
What causes diseases such as albinism II, Wilson’s disease and cystic fibrosis?
A lack of/ damage to transport mechanisms in the cell membrane
Name four roles of membrane proteins
Signal transduction (relay messages into cell, to grow, divide etc.) Cell recognition (of invading cells) Intercellular joining (cell junctions) Linking cytoskeleton and ECM
What is included in the endomembrane system? (7)
Nuclear envelope ER Golgi apparatus Vesicles Lysosomes Vacuoles Plasma membrane
How is the endomembrane system connected?
By direct physical contact, and transfer by vesicles
What are the two regions of the ER?
Smooth and rough
sER and rER
Which region of the ER can be increased or decreased to meet the cell’s demands?
sER
Functions of sER (4)
Metabolises carbohydrates
Synthesises lipids for membranes
Detoxifies drugs/ poisons
Stores calcium ions
What is a main function of the smooth ER in liver cells?
Detoxifying drugs and poisons e.g. alcohol
Function of rER
Synthesising proteins
How does the rER process proteins?
They move into the lumen of the rER, are folded into shape, are processed then move to the Golgi complex.
Describe the structure of the Golgi apparatus
A complex made of flattened tubules with a cis face and a trans face.
Functions of Golgi apparatus
Organises, modifies and sorts proteins
Describe the travel of proteins through the Golgi apparatus
Arrive at cis face from the rER, leave at the trans face in vesicles
What is the name of the process that adds/ modifies carbohydrates to proteins in the Golgi apparatus?
Glycosylation
Which proteins is glycosylation important for?
Cell surface and secreted proteins
How does the Golgi apparatus direct proteins out into the cell?
Molecular markers are added to the proteins. They leave in vesicles which are also tagged with markers of short proteins. These act as barcodes
Where are proteins directed to from the Golgi apparatus?
Lysosomes, plasma membrane or secretion
Two categories of bulk transport
Exocytosis (out of the cell) and endocytosis (into the cell)
Two types of exocytosis
Constitutive exocytosis
Regulated exocytosis
Which process continuously releases ECM proteins?
Constitutive exocytosis
Bulk transport
Form of transport of glycoproteins across the plasma membrane
Describe regulated exocytosis
A signal is required to move vesicles in the cell which release hormones and neurotransmitters into the ECM
Phagocytosis
A pseudopodium stretches out of the cell, forming a phagocytic vacuole.
This vacuole traps particles (like food), then merged with a lysosome which digests the food particles.
What do lysosomes contain?
Hyrdolytic enzymes which break the bonds between particles
Macrophages
White blood cells
Which type of bulk transport occurs in macrophages?
Phagocytosis- it takes in bacteria to fight.
Pinocytosis
Form of bulk transport (endocytosis) which forms a vacuole in the cell wall.
The vacuole is lined with protein called coat protein. This helps direct the vacuole in the right direction.
Receptor-mediated endocytosis
A specialised form of pinocytosis which is selective about the solute captured into the vacuole.
Receptors sit on the cell membrane, and the vacuole forms once a bulk quantity of the required solute is captured.
What is the pH level hydrolytic enzymes require to function well?
Low pH (acidic)
What are lysosomes made by?
rER and Golgi apparatus
Lysosome functions (2)
To break down proteins, lipids, carbohydrates and nucleic acids
To recycle unwanted cellular materials
Autophagy
Process of cell eating itself/ breaking down. Performed in lysosomes.
Important for cell health and to facilitate cell death
What is Tay-Sachs disease caused by?
Hydrolytic enzymes in the lysosomes aren’t able to properly break down molecules, which build up in cells and damage the kidneys, eyes, brain.
Vacuoles
Large vesicles derived from the rER and Golgi. Unlike other vesicles, their membranes cannot fuse with others.
Function of cytoskeleton
Maintain cell shape and organelle positions
Allows change in cell shape by disassembling/ reassembling rapidly
Three components of the cytoskeleton
Microtubules
Intermediate filaments
Microfilaments
Which component of the cytoskeleton is the smallest?
Microfilaments
Microtubules
A component of the cytoskeleton. Made of tubular subunits.
Functions of microtubules (3)
Maintain cell shape by resisting compression
Provide cell motility
Provide organelle motility
What structures can microtubules make up to provide cell motility?
Flagella and cilia
Describe the movements of flagella and cilia
Flagella- few per cell- have a snake-like motion
Cilia- lots per cell- have a rowing-like motion (undulating)
These can move the cell itself, or move fluid past it.
How are microtubules organised?
They can radiate out from a centrosome, or can be arranged alongside each other
How do microtubules facilitate organelle motility?
ATP-powered motor proteins can ‘walk’ along the microtubules, transporting an attached vesicle/ organelle to a different part of the cell
Describe the structure of microfilaments
A double chain of actin subunits, which can form linear strands or 3D networks.
Function of microfilaments
To resist tension- e.g. the cortical network under plasma membrane helps maintain cell shape by making it less fluid
What happens when microfilaments (actin) and motor proteins interact?
Muscle contraction
Amoeboid movement
Cytoplasmic streaming (plants)
Intermediate filaments structure
Composed of various proteins e.g. keratins (hair), lamins (nucleus), neurofilaments (neurons)
They are supercoiled into cables.
Functions of intermediate filaments
Maintain cell shape- more long lasting than other components
Anchor organelles in place
Three types of cell junction
Tight junctions
Desmosomes
Gap junctions
How do tight junctions connect cells?
Press neighbouring cells tightly together by attaching the microfilaments networks beneath the plasma membrane (cortical network).
Function of tight junctions?
Prevents movement of fluid across cell layer
How do desmosomes connect cells?
Anchor them together via intermediate filaments.
A torn muscle is a torn _____?
Desmosome
Gap junction structure
Proteins, arranged with a pore in the middle, attach the two cells.
Function of gap junctions
Allows rapid communication between cells. Ions and small molecules can pass through quickly.
Do all cells make direct contact with each other?
No. Some lie with an ECM
What is the ECM composed of?
Material secreted by cells. Includes various proteins
Which glycoproteins is most abundant in the ECM?
Collagen
What do proteoglycans do in the ECM?
Trap water to help it keep shape
Complex matrix proteoglycans
Proteins with extensive sugar additions
Fibronectins
Glycoproteins that attach cells to the ECM
Integrins
Proteins that connect the ECM to the cytoskeleton
Protoplast (5)
The term used to describe inside the plant cell (so not including cell wall)
Nucleus Golgi apparatus Central vacuole Mitochondrion Chloroplast
Two phases of the plant cell wall
Cellulose
Noncrystalline matrix
Cellulose structure
Glucose polymer
Highly organised and strong
Cellulose molecules bond to form microfibrils
What two polysaccharides are in the noncrystalline matrix?
Pectin and hemicellulose
What is pectin and what is it’s function?
Branched, negatively charged polysaccharides
They bind water with their gel-like properties
Hemicellulose and it’s structure
Heterogenous group of polysaccharides
A long chain of one sugar type with short side chains
Strengthen cell wall
Extensin
A protein with dehydrated the cell wall by cross-linking with pectin
This reduces extensibility and increases strength if the cell wall
Rosette
An enzyme complex at the cell wall which produces cellulose
Three parts of primary cell wall synthesis. What type of transport is performed?
Cellulose microfibrils laid down at plasma membrane
Polysaccharides are transported in vesicles from Golgi to the cell wall
Cell wall proteins (e.g. extensins) are transported to the cell wall
Constitutive exocytosis
What determines where the microfibrils are laid during primary cell wall synthesis?
Cortical microtubules. Rosettes start at one end and travel parallel to the cortical microtubules as they lay down the microfibrils.
Middle lamella
In between the primary and secondary cell walls. Made up of pectin mostly
Functions of cell wall
Influences cell morphology (it’s shape, size, form etc.)
Provides structural support
Prevents excessive water uptake
What in the cell wall influences the cell’s morphology?
The orientation of microfibrils.
When arranged parallel to long axis- the cell will expand longitudinally
When arranged randomly, the cell will expand equally in all directions
What will cause the cell to shrivel up?
Water loss
How does the cell wall prevent excessive water uptake?
The cell wall pressure limits the volume of water it can take- it restricts the protoplast from expanding too far.
How many membranes do vacuoles have?
One
Hypotonic
Too much water
Hypertonic
Not enough water
Isotonic
Just right amount of water
Do all plant cells have a secondary cell wall?
No
Which cell wall is thicker?
Secondary
Which layers make up the secondary cell wall?
S1, S2 and S3
What makes the layers in the secondary cell wall different?
Different orientations of microfibrils- this adds strength
Does the secondary cell wall have more or less cellulose, and more or less pectin?
More cellulose, less pectin
Which macromolecule can be found in the secondary cell wall but not the primary one?
Lignin
Describe lignin
Second most abundant organic macromolecule to cellulose
Complex polymer
Very strong and rigid. Excludes water
Plasmodesmata
What do they allow?
Intercellular connections allowing cells to communicate. They are pores in the cell wall.
Allow free exchange of small molecules- organelles cannot pass through.
Does the plasma membrane stop at plasmodesmata?
It is continuous with the plasma membrane of the other cell at the pore.
What main reaction occurs in photosynthesis?
Light energy transferred into chemical energy in organic molecules
By product of photosynthesis
O2
Where does photosynthesis take place?
In the chloroplasts in plant cells
ATP
Adenosine Triphosphate, an energy carrier
What makes up ATP?
Adenine, ribose and a triphosphate group
What has to happen for energy to be released from ATP?
One phosphate is removed, turning ATP into ADP adenosine diphosphate
What does the cell require energy for?
Mechanical walk
Making new materials
Power active transport
Maintain order (fight entropy)
Reaction occurring in mitochondria
C6H12O6 + 6O2 —> 6CO2 + 6H2O + energy
How many mitochondria per cell? What does the number depend on?
1-1000’s
Depends on energy demand
What does the mitochondrion contain?
Mitochondrial DNA and ribosomes
Cristae
Folds in the inner membrane of the mitochondrion
Three stages of cellular respiration
Glycolysis
Pyruvate oxidation + citric acid cycle
Oxidative phosphorylation
Describe the glycolysis stage of cellular respiration
Glucose 6C molecule is split in half into two pyruvate 3C molecules.
2ATP released.
Electrons transferred to -NAD+ which becomes NADH
NADH
A high energy electron carrier
Describe the pyruvate oxidation and citric acid cycle stage of cellular respiration
Pyruvate 3C converted into Acetyl CoA
More electrons to NADH
Acetyl CoA enters the citric acid cycle
More electrons to NADH. Some higher energy electrons go to FADH2
2 ATP released
Describe the oxidative phosphorylation stage of cellular respiration
1: proton gradient is generated
Protons pumped by electron carriers accumulate in inter membrane space. Energy for this comes from electrons
2: chemiosmosis
Proton gradient causes protons to move back into matrix. This powers ATP synthase
ADP + Pi —> ATP
ATP synthase
Protein complex that synthesises ATP molecules from ADP and Pi
What process is responsible for almost all of the planet’s energy resources?
Photosynthesis
What are the two products of photosynthesis?
Organic molecules and O2
What are the two products of cellular respiration?
CO2 and H2O
What are the two parts of photosynthesis?
Light reactions and Calvin cycle
Where in the plant cell does photosynthesis occur?
In the chloroplasts
How many membranes do chloroplasts have?
Three
What membrane-bound compartments make up the central membrane system of a chloroplast?
Thylakoids
Granum
A stack of thylakoids
Light reactions (photosynthesis)
Light is captured in the thylakoids and converted to chemical energy in the form of ADP and NADH
Calvin cycle (photosynthesis)
ATP and NADPH drive the reactions to turn CO2 into carbohydrates (3 carbon sugars)
Stroma
Fluid-filled space within the chloroplast, surrounding the grana
What is the name of the system which moves electrons during photosynthesis?
Photosynthetic electron chain
Photosystems
Protein complexes in the thylakoid membranes that work together to carry out photosynthesis.
Which part of a photosystem is able to absorb light energy?
Chlorophyll
How are the two photosystems in photosynthesis connected?
By the electron transport chain
What happens after light energy is absorbed in photosystem II?
Electrons get excited, and enter the electron chain
What are the electrons leaving photosystem II replaced by?
Electrons taken from H2O molecules
How is O2 produced during the light reactions?
By stripping electrons from H2O molecules to replace excites electrons which have left the photosystems
What does the energy from electrons go towards in the photosynthetic electron chain?
Pumping hydrogen ions from the stroma into the thylakoid
What powers ATP synthase?
The high concentration of hydrogen ions inside the thylakoid
How does NADPH function in the light reactions?
It captures excited electrons from photosystem I.
What are the two energy products of the light reactions in photosynthesis?
ATP and NADPH
Where does the Calvin cycle take place?
In the stroma of the chloroplast
What is the reaction that takes place in ATP synthase?
ADP + phosphate group —> ATP
Cytochrome complex
A complex used to pump protons through the thylakoid membrane by using energy from electrons from photosystem II
List the three parts of the Calvin cycle
Fixation
Reduction
Regeneration
Describe carbon fixation
Low energy CO2 is fixed into sugars.
Three CO2 molecules react with three 5-carbon molecules to produce six 3-carbon sugars.
3CO2 + 3(5C) —> 6(3C)
Describe reduction in the Calvin cycle
The six 3-carbon sugars are converted into slightly different 3-carbon sugars.
This step requires energy from ATP and NADPH.
How much ATP and NADPH is needed for reduction in the Calvin cycle?
One molecule of each per carbon sugar.
Describe regeneration in the Calvin cycle.
One 3-carbon sugar has exited, and we are left with five 3-carbon sugars.
These five 3-carbon sugars are used to regenerate the starting molecules (three 5-carbons) required for the fixation step.
3ATP is needed for this (one per 5-carbon product)
Inputs of photosynthesis (3)
Light
Water
Carbon dioxide
Main difference in cellular respiration between plants and animals
Animals must source their glucose externally, while plants generate their own (Calvin cycle)
Difference between electron transport chains in cellular respiration of plants and animals
It pumps H+ ions into inter-membrane space for animals, and thylakoid space for plants
Describe the theory of endosymbiosis
An ancestral host cell engulfed a cyanobacterium. Instead of digesting it, the host cell kept it because it benefited the cell (photosynthesis). Eventually the genes of the bacterial cell merged with those of the host cell, and the cell reproduced.
Over generations, the engulfed cell became an organelle.
How large is the nucleus?
5-10 micrometres
Where are most of the cells genes found?
In the nucleus
What makes red blood cells different to other animal cells?
They have no nucleus- takes up too much room in a cell whose job is to transport oxygen
Where are genes found in the cell?
Nucleus, mitochondria and chloroplasts
Functions of nucleus (2)
Protects genes
Controls cell
Perinuclear space
The space between the two membranes of the nucleus
Nuclear envelope
Two lipid bilayer membranes that surround the nucleus
What is continuous with the perinuclear space?
Lumen of ER
What is continuous with the outer membrane of the nucleus?
ER membrane
Nuclear pore complex
Pores scattered on the surface of the nuclear outer membrane.
They control the movement of particles into/ out of the nucleus
What travels out of the nucleus? (3)
mRNA
tRNA
Ribosomal subunits
What is tRNA and it’s function?
Transfer RNA
Carries information from a gene
What is mRNA and it’s function?
Messenger RNA
Needed to build ribosomal subunits
What travels into the nucleus? (3)
Energy
Control signals
Building materials for RNA
In what forms does energy enter the nucleus? (3)
Proteins
Carbohydrates
Lipids
What is the process of moving particles into/ out of the nucleus called?
Nucleocytoplasmic exchange
Nuclear lamina
Sheet of intermediate filaments that form a mesh work inside the nucleus
Two functions of nuclear lamina
Maintains shape of nucleus
Organises packing of DNA
How does a detective nuclear lamina effect the cell?
How it divides
It’s behaviour e.g. premature aging
Nucleolus
Prominent structure within the nucleus of non-dividing cells
Function of nucleolus
Produce ribosomal RNA
What does ribosomal RNA produce in the cell? What does it combine with?
Ribosomes- by combining with proteins
How much DNA does each cell contain? How does this compare to the size of the cell?
~2.5m
250 000 times the diameter of the nucleus
How does DNA fit within the nucleus?
It is tightly packed into dense fibres (chromosomes when dividing)
How large in diameter is a DNA double helix?
~2nm
Histones
Proteins that serve as a spool for the DNA helix to wrap around almost twice
How many histones are there and what are they called?
8
H2a (2)
H2b (2)
H3 (2)
H4 (2)
What are the ‘beads’ called that are formed by DNA helix wrapping around a histone?
Nucleosomes
How does DNA further condense after wrapping into nucleosomes?
Into a 10nm fibre
Then a 30nm fibre
Then a 300nm fibre
Then a metaphase chromosome (but only if undergoing cell division)
List the packing steps of DNA
Double helix —> nucleosomes —> 10nm fibre —> 30nm fibre —> 300nm fibre —> metaphase chromosome (when dividing)
Euchromatin
A less dense region in a chromosome which contains genes that are being used
Heterochromatin
A more dense region in a chromosome containing genes not being used by the cell
Which regions in a chromosome are darker?
Heterochromatin
What do chromosomes consist of? (2)
Nucleic acid
Proteins
DNA varies between species. What does this show?
That DNA is the genetic material differentiating species
Chargaff’s two rules
Base pairing: A to T and G to C
The composition of DNA varies between species
What makes up the Watson-Crick model of DNA structure? (5)
DNA has a double-stranded helix a structure
Sugar phosphate backbone on the outside
Based on the inside
Stabilised by hydrogen bonds
The two polynucleotide strands run anti parallel
How are the nucleotides of nucleic acids joined together?
By phosphodiester bonds
In which direction is the polynucleotide synthesised?
5’ end to 3’ end
How many bonds join adenine to thymine?
Two hydrogen bonds
How many bonds join guanine to cytosine?
Three hydrogen bonds
What stabilises the DNA molecule?
Hydrogen bonds
Which parts of the nucleotides do the phosphodiester bonds attach?
The 3’ hydroxyl group and the 5’ phosphate group.
What kind of reaction occurs when a phosphodiester bond is formed? Why?
Condensation reaction, because an H2O molecule is formed.
OH from 3’ hydroxyl group, and H from 5’ phosphate group
Where does DNA replication occur?
At origins of replication
Why are there multiple origins of replication?
Because a single origin would take too long
What is the point where a DNA strand is untwisting called?
Replication fork
Helicase
Enzymes which pull the two parental strands of a DNA helix apart.
Pulls like a zipper- travels as it pulls
Topoisomerase
Enzymes which release tension and unwind the strands ahead of the replication fork
Primase
An enzyme containing a 3’ hydroxyl group, which it uses to synthesise an RNA primer, which ends in a phosphate group.
DNA pol III
Synthesises DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand
Single-strand binding proteins
Bonds to single strands of DNA to protect from other enzymes and keep the two parental strands apart
DNA pol I
Enzyme which removes RNA primer nucleotides and replaces them with DNA nucleotides. It leaves fragments of DNA that aren’t linked by phosphodiester bonds.
DNA ligase
Enzyme which forms a phosphodiester bond between two Ogazaki fragments.
e.g. joins lagging strand parts into one, as well as joining the strands of adjacent bubbles
Why do lagging strands exist?
As the helicase unwinds more of the DNA helix, more of the 3’ end is exposed as single strands to replicate.
Since DNA pol III can only synthesise from 5’ to 3’, and the daughter strand must run antiparallel to the parent strand, only fragments of DNA can be synthesises at a time.
Exonuclease
Enzyme (DNA pol III) which repairs errors in DNA by removing nucleotides from the end of the strand.
Occurs during replication
Endonuclease
Enzyme (DNA pol III) which repairs errors in DNA by removing bases at any point of the strand.
Occurs after replication.
How does DNA pol III perform exonuclease activity?
As it synthesises the strand, it detects an incorrect base, removes it, then continues synthesis.
How does DNA pol III perform endonuclease activity? What other enzyme is involved?
After synthesis, it takes a chunk of bases out of the strand- one of which is the incorrect base. It replaces with the correct bases.
DNA ligase forms phosphodiester bonds to join the new nucleotides to the strand.
What happens if an error in DNA is not corrected?
Incorrect bases is passed down to daughter cells, which leads to permanent DNA change or mutation.
PCR
Polymerase chain reaction
It is used to make large quantities of DNA copies (in vitro replication)
Why do we use in vitro replication?
When we want a large amount of material to work with- for example when examining a disease
What are the three steps of PCR?
Denaturation
Annealing
Extension
Denaturation (PCR)
DNA is heated to 94-98 degrees Celsius, strands separate
Annealing (PCR)
DNA is cooked to 45-70 degrees Celsius, allowing primers to base pair to parental strand
Extension (PCR)
72 degrees Celsius, polymerase extends primer to form a nascent DNA strand
How many DNA copies do we get after 30 rounds of PCR?
Two billion
Nascent DNA strand
A DNA strand which has just come into existence
Karyotype
An ordered visual representation of chromosomes in a cell
How do we make a karyotype? (3)
Take blood sample
Treat with mutagen, colchicine and stain
Organise pictures by pairing homologous chromosomes
Each chromosome is made of two ___?
Chromatids
Homologous pairs 1-22 are called ____?
Autosomes
What are the differences between X and Y chromosomes?
Y is smaller and contains less genes
Locus
Particular location on a chromosome where a particular gene is found
Gene
Sequence of nucleotides in a chromosome that determine a specific trait
Alleles
Different forms of a gene
Homozygote
An individual who has two of the same allele
Heterozygote
An individual who has two different alleles
What does cell division allow? (3)
Development from a fertilised cell
Growth from foetus to adult
Repair of cells/ tissue
Mitosis
Cell division that produces two genetically identical daughter cells
Two main phases of cell cycle
Interphase
Mitotic phase
How much of the cell cycle does interphase take up?
90%
Three phases in interphase
Growth 1 (G1) Synthesis Growth 2 (G2)
Two phases within mitotic phase
Mitosis
Cytokinesis
Five phases of mitosis
Prophase Prometaphase Metaphase Anaphase Telophase
Describe prophase
Occurs after G2
Chromosomes condense and become visible as a sister chromatin pair
Early mitotic spindle develops
What does the mitotic spindle develop from?
Disassembled cytoskeleton
At what point are two sister chromatids connected?
Centromere
What appear at the two ends of the mitotic spindle?
Centrosomes (clusters of microtubules)
Describe prometaphase
Occurs after prophase
Nuclear envelope fragments
Microtubules extend from mitotic spindle and attach to kinetochores of sister chromatid pairs
Kinetochore microtubules
Microtubules that attach to the kinetochores of sister chromatids
Nonkinetochore microtubules
Microtubules that don’t attach to the kinetochores of sister chromatids
Metaphase
Occurs after prometaphase
Kinetochore microtubules pull at each sister chromatid of a pair until they settle at the metaphase plate
What is the imaginary equator of the cell called?
Metaphase plate
Describe anaphase
Occurs after metaphase
Kinetochore microtubules shorten, which pulls sister chromatids apart, towards the piles of the cell
Nonkinetochore microtubules lengthen, pushing and widening the cell
Describe telophase
Occurs after anaphase
Cleavage furrow forms in centre of cell, forming two connected cell shapes.
Nuclear envelopes form around the chromatids at each pole of the cell
Cytokinesis
Splitting of the cell into two daughter cells (occurs during telophase)
What causes the cleavage furrow?
A ring of actin filaments contracting around the parent cell
Haploid cell
A cell with one set of chromosomes
Diploid cell
A cell with two sets of chromosomes
Meiosis
A process of cell division that halves the number of chromosomes going into gametes
Explain the sexual life cycle
Meiosis of parent cell produces haploid gametes- eggs or sperm with a single set of chromosomes
Two gametes fuse (fertilisation) to form a diploid zygote with the original number of chromosomes is the same as the parent cell
Three basic phases of meiosis
Interphase- Chromosomes duplicate
Meiosis I- Homologous chromosomes separate
Meiosis II- Sister chromatids separate
Prophase I (meiosis)
Occurs after interphase
Homologous chromosome pairs align and synapse (two pairs join)
Crossing over occurs between non-sister chromatids at chiasmata
Mitotic spindle is forming and nuclear envelope fragments like mitosis
What does crossing over result in?
Chromatids being a mix of pieces from each chromosome
Describe metaphase I (meiosis)
The chiasmata of paired homologous chromosomes line up with the metaphase plate
How many chromosome pairs are at the metaphase plate in meiosis I, compared to the number of chromosomes in mitosis?
Half as many chromosome pairs in meiosis I as chromosomes in mitosis
Describe anaphase I (meiosis)
Recombined homologous chromosomes separate, but sister chromatids remain attached
Describe telophase I (meiosis) (and cytokinesis)
Cleavage furrow causes haploid cells with duplicated chromosomes to form
What is different about the two cells formed from meiosis I, and the two formed from mitosis?
The two cells formed from meiosis I are haploid cells- they only have half the genetic information in each cell. Their chromosomes are also duplicated (for division in meiosis II)
Differences between mitosis and meiosis I (5)
In mitosis, chromosomes align independently. In meiosis, homologous chromosomes synapse.
Meiosis has chiasmata.
Mitosis has centromeres on metaphase plate, meiosis has chiasmata.
Chromatids disjoin during mitosis, while chromosomes disjoin during meiosis.
2n—>2n (diploid cell formed) for mitosis
2n—>n (haploid cells formed) for meiosis
Advantage of asexual reproduction
Can produce a much larger number of offspring
Advantage of sexual reproduction
Produces much more genetic diversity
How does genetic diversity arise from sexual reproduction? (3)
Independent assortment of chromosomes (organised indecently during metaphase)
Crossing over between non-sister chromatids
Random fertilisation of gametes
In what circumstances does genetic diversity allow for better survival? (3)
Spatially variable environments (climate, ecology etc)
Changing environments (parasites, seasons etc)
Sib-sib competition (different siblings will utilise resources differently)
