2. cells

summarise the difference (in products) between mitosis and meiosis

mitosis: produces 2 daughter nuclei each w/ the same number of chromosomes as the parent cell and each other

meiosis: produces 4 daughter nuclei w/ half the number of chromosomes as the parent cell

name the 3 stages of interphase:

• G1 (growth stage 1)

• S (synthesis)

• G2 (growth stage 2)

what occurs in G1 of interphase?

• cell grows

• proteins synthesised

• organelles replicate → prepares for DNA replication

what occurs in S of interphase?

DNA is replicated

what occurs in G2 of interphase?

• cell finishes growing

• protein synthesised → prepares for cell division

what is mitosis significant for?

• growth

• repair

• differentiation

what are the stages of the cell cycle?

• interphase (made up of G1, S and G2)

• Prophase

• Metaphase

• Anaphase

• Telophase

• cytokinesis

  

what is the centrosome? what are some of its key features?

• where spindle fibres grow from

• located near the nucleus

• not present in plants/fungi

• in cytoplasm?

• 1 centrosome contains 2 centrioles

  

what is the centriole?

• 1 centriole = 9 groups of microtubules

• spherical shape

  

what happens (generally) during interphase?

• DNA replication

• Organelle (including centrosomes) duplication

• Cell growth

• Transcription/translation

• Obtain nutrients

• Respiration

what happens during prophase?

• chromosomes condense so they become visible

• chromosomes attach to spindle fibres (/metaphase)

• nucleolus disappears and nuclear envelope breaks down

what happens during metaphase?

chromosomes arrange along middle of cell:

• spindle fibres form from centrioles

• chromosomes line up along spindle fibres across middle of cell

what happens during anaphase?

• centromeres divide

• sister chromatids pulled to opposite poles of cell

• spindle fibres shorten (/prophase/metaphase)

what happens during telophase?

nuclear envelope reforms:

• spindle fibres disintegrate

• nucleolus reforms

• nuclear membrane reforms

• chromosomes decondense

what happens during cytokinesis?

division of the cytoplasm and cell membrane into 2 genetically identical daughter cells

what is the proteome?

all of the proteins in an organism (essentially like the genome but for proteins)

what is the centromere?

centre of a chromosome, where spindle fibres attach

explain the difference between a chromosome and a chromatid

• chromosome = DNA molecule that contains part of the genetic material of an organism

• chromatid = one arm of a duplicated chromosome - one copy of a newly copied chromosome

• (confusingly, chromosomes can look like I or X)

what is a cell?

smallest building block in an organism and are capable of carrying out specific functions

how are cells able to carry out different functions?

differentiation

what is ultrastructure?

the internal structure of a cell as not visible on a light microscope

what are the three domains of all living things?

• archaea

• bacteria

• eukaryota

what is a cell made of (main groups)?

• proteins

• polysaccharides

• lipids

• nucleic acids

what is the significance of the proteins w/in a cell?

• enzymes in the cytoplasm and inside organelles

• associated w/ the membrane

• associated w/ DNA in the nucleus

• associated w/ RNA in ribosomes

• cytoskeleton

what is the significance of the polysaccharides w/ in a cell?

• associated w/ the membrane

• makes up cell walls

• stored for energy reserve

what is the significance of the lipids w/in a cell?

• stored for energy reserve

• phospholipids make up cell membranes

• cholesterol associated w/ membrane and controls fluidity

where are the nucleic acids w/in the cell found?

• DNA: associated w/ proteins in the nucleus

• RNA: mRNA, rRNA, tRNA - different types found in nucleus or cytoplasm or associated w/ proteins in ribosomes

what is the function of the nucleus?

• contains genetic material for polypeptides

• DNA replication

• production of mRNA/tRNA/transcription

• production of rRNA/ribosomes

what is the structure of the nucleus?

• nuclear envelope/double membrane and pores

• chromosomes/chromatin/DNA w/ histones

• nucleolus/nucleoli

what is the difference between chromosomes and chromatin?

chromosomes:

• linear molecule of DNA tightly wrapped around histone proteins

• DNA is only in this form during cell division

chromatin:

• DNA more loosely associated w/ histones

• enclosed in the nucleus

what are the two types of endoplasmic reticulum (ER)?

• rough endoplasmic reticulum (RER)?

• smooth endoplasmic reticulum (SER)?

what is the structure of the RER?

• continuous w/ the nuclear membrane, membrane bound

• has ribosomes on cisternae

what is the function of the RER?

• cisternae provide large SA for protein synthesis

• protein collects inside RER and transported throughout cell

what is the structure of the SER?

• membrane bound

• no ribosomes (hence smooth)

• more tubular than RER

what is the function of the SER?

synthesises, stores and transports lipids, steroids and carbohydrates

what is the function of the ribosomes?

site of protein synthesis

what is the structure of the ribosomes?

• made up of ribosomal RNA (rRNA) and protein

• consists of a large and small subunit

• two types: 80S (found in eukaryotic cells) and 70S (found in prokaryotic cells, mitochondria and chloroplasts)

what is the structure of the Golgi apparatus?

• membrane bound

• stacks of cisternae (flattened, membrane bound sacs)

• vesicles are continuously pinched off from the ends

what is the function of the Golgi apparatus?

• modifying/packaging/transporting proteins/glycoproteins

• modifying/packaging/transporting lipids/glycolipids

• form vesicles and lysosomes (as they are Golgi vesicles)

what events take place when a protein is made and sent to the extracellular space?

• a gene is transcribed into mRNA in the nucleus

• the mRNA leaves through a nuclear pore

• the mRNA reaches a ribosome on the RER

• the ribosome synthesises a protein into the RER

• the protein is packed in a vesicle that leaves the RER

• the vesicle reaches the golgi and fuses w/ its cisternae

• the protein is released outside

what are lysosomes?

type of Golgi vesicle containing hydrolytic enzymes (proteases, lipases, lysozymes)

what is the function of lysosomes?

digests unwanted material in the cell:

• hydrolyses material ingested by phagocytic cell

• exocytosis - releases enzymes to outside of cell to destroy material

• digests worn out organelles

• autolysis - complete breakdown of cells after they have died

what is the function of the mitochondria?

• site of aerobic respiration

• releases ATP during respiration - source of energy for cell activities

what is the structure of the mitochondria?

• double membraned (membrane bound) - inner membrane folds to form cristae, where respiratory enzymes are embedded

• fluid centre = mitochondrial matrix - also contains respiratory enzymes as well as loop of mitochondrial DNA, proteins, lipids and ribosomes

give the 4 main steps of cell fractionation:

• sample preparation

• homogenisation

• filtration

• ultracentrifugation

describe the sample preparation stage:

sample is placed in an ice cold, isotonic, buffered solution

why must the solution used in sample preparation be ice-cold?

reduce enzyme activity that might otherwise digest organelles

why must the solution used in sample preparation be isotonic?

ensures ψ inside and outside organelles is the same, so they do not burst as a result of osmosis

why must the solution used in sample preparation be buffered?

keeps pH constant so that organelle structures are not damaged and enzymes do not denature

describe and explain the homogenisation stage:

• cells are broken open

• this disrupts the plasma membrane, allowing the organelles to be released into the solution

describe the filtration stage:

mixture filtered to remove cellular debris and tissue fragments

describe the ultracentrifugation stage:

• filtrate centrifuged at a low speed → dense organelles (nuclei) form pellet at bottom of tube, less dense organelles remain suspended in supernatant

• supernatant transferred to new tube and centrifuged at a higher speed → next heaviest organelles (chloroplasts/mitochondria) settle out

• transfer supernatant into new tube and repeat entire process, increasing speed each time until all organelles have been separated into distinct layers

give the order of organelles from heaviest to lightest:

• nuclei

• chloroplasts

• mitochondria

• lysosomes

• ER

• ribosomes

what is the pellet?

sediment at bottom of tube - contains heavier organelles

what is the supernatant?

liquid remaining above pellet - contains lighter organelles

what is the function of the chloroplasts?

site of photosynthesis

what is the structure of the chloroplasts?

• double membraned

• grana - sticks of disc like structures called thylakoids (membranes that contain photosynthetic pigment - chlorophyll)

• stroma - fluid filled matrix containing enzymes for photosynthesis

• contain both DNA and ribosomes

what is the structure of the vacuole?

fluid filled sac surrounded by a membrane called tonoplast

what is the function of the vacuole?

• makes cells turgid by pushing cytoplasm against cell wall → provides support

• temporary store of sugars and amino acids

• stores and excretes waste products

• pigments may give cell colour

what is the function of the cell wall?

• provides structural support and strength to the cell

• prevents cell from bursting under osmotic pressure

what is a plant cell wall made up of?

cellulose microfibrals

what is an algal cell wall made up of?

cellulose and/or glycoproteins

what is a fungal cell wall made up of?

chitin, glycan and glycoproteins

outline the similarities in and the differences between the structures of chloroplasts and mitochondria (4):

accept chloroplasts have chlorophyll whereas mitochondria do not

what are the 3 key types of microscope?

• optical/light microscope

• transmission electron microscope

• scanning electron microscope

what is magnification?

how many times larger an image is compared to the object

what is resolution?

minimum distance between 2 objects in which they can still be viewed as separate

how do you convert from mm → µm?

x1000

how do you convert from µm → nm?

x1000

what is the equation for magnification?

magnification = image size/object size

what is an eyepiece graticule?

• circular piece of glass/plastic that sits on a ledge in the eyepiece, w/ a scale engraved into it

• will always appear the same no matter the magnification

what is a stage micrometer?

• slide w/ a very accurate scale engraved into the glass, placed on microscope stage

• distance between lines remains same no matter the magnification

why must we calibrate the eyepiece graticule?

graticule scale is arbitrary (represents different lengths for different magnifications), so needs to be calibrated for any new microscope or new magnification

how does a light microscope work? what is its max magnification and resolution?

• visible light is bent through the lens system to enable the user to see the specimen

• max resolving power = 0.2 µm

• max magnification = x1500

evaluate the use of a light microscope:

strengths:

• living specimens can be viewed

limitations:

• much lower resolving power and magnification compared to electron microscopes

• stains must be used, as cells transparent and components not distinguishable, which usually kills cells

• specimen must be extremely thin for light to pass through

a scientists prepared alveolar tissue to view using optical microscope. the scientist cut very thin slices of the alveolar tissue.

explain why the scientist used very thin slices of alveolar tissue with the optical microscope (2)

what is the maximum magnification and resolution of a transmission electron microscope and scanning electron microscope?

• max magnification = x1,500,000

• max resolving power = 0.0002 µm (TEM), 0.02 µm (SEM)

how does a transmission electron microscope work?

• electron beam penetrates the cell, providing details of cell’s internal structure

• denser parts of specimen absorb more electrons, making them look darker - this is how an image is formed

evaluate the use of a transmission electron microscope:

strengths:

• higher resolving power and magnification than light microscopes

limitations:

• can only be used on thin specimens

• complex staining process

• b&w image

• can only be used on dead specimens as system must be in a vacuum

• may contain artefacts as a result of how the specimen is prepared

how does a scanning electron microscope work?

• beam of electrons moves across specimen, knocking electrons off the specimen

• electrons gathered in a cathode ray tube - this is how an image is formed

evaluate the use of a scanning electron microscope:

strengths:

• higher resolving power and magnification than light microscopes

• produces 3D images

limitations:

• complex staining process

• b&w image

• can only be used on dead specimens as system must be in a vacuum

• may contain artefacts as a result of how the specimen is prepared

• lower resolving power than transmission electron microscope

what is a bacterial cell wall made up of?

murein (peptidoglycan)

give 2 features of all prokaryotic cells that are not features of eukaryotic cells (1)

reject plasmids - smaller versions of circular DNA which are not necessary for survival

give 3 structural features found in all virus particles and describe their function:

• capsid - protects genetic material

• genetic material - codes for viral protein

• attachment protein - to bind to receptors on cell

name the 7 key structural components of a general bacterial cell

• flagellum

• genetic material (circular and plasmids)

• cytoplasm

• ribosomes

• capsule

• murein cell wall

• cell membrane

describe the process of binary fission:

• circular DNA and plasmids replicate (main DNA loop only replicated once but plasmids can be replicated many times)

• cell grows and DNA loops move to opposite poles of cell

• cytoplasm begins to divide and new cell walls begin to form

• cytoplasm divides and 2 daughter cells are produced w/ 1 copy of circular DNA but a variable no. of copies of plasmids

describe viral replication (3)

• attachment proteins attach to receptors

• nucleic acid/DNA/RNA enters cell

• nucleic acid replicated in cell/reverse transcriptase makes DNA from RNA

• cell produces protein/capsid/enzymes

• virus assembled and released from cell

why are viruses described as acellular and non living? (2)

• not made of cells/no cell surface membrane

• no metabolism/nutrition

give one reason why antibiotics are ineffective against viruses:

any 1 from:

• do not have bacterial structure/enzymes

• do not have metabolism

• do not have cell wall/murein

describe the differences between active and passive immunity (5)

can you label this antibody?

yes

how do antibodies help to destroy pathogens?

• bind and neutralise toxins

• agglutination

what is agglutination? why is it significant?

• antibodies are flexible, which cause pathogens to clump together

• → this makes the pathogens easier to locate and destroy by phagocytes

draw the shape of the primary/secondary immune response graph:

explain the shape of the primary/secondary immune response graph:

primary immune response:

• takes time for clonal selection and expansion of specific T and B cells

• antibodies do not begin to appear in the blood for several days after the foreign antigen enters the body (this is when symptoms occur)

• some B cells differentiate during clonal expansion into plasma cells and memory cells but plasma cells are short lived :(

secondary immune response:

• B memory cells recognise antigen and quickly / and differentiate into plasma cells and more memory cells

• antibodies made more quickly and in a higher conc → pathogens killed before symptoms develop

what is active immunity?

immunity developed after immune system makes its own antibodies

what is natural active immunity?

immunity developed after immune system makes its own antibodies following infection

what is artificial active immunity?

immunity developed after immune system makes its own antibodies following vaccination

what is passive immunity?

immunity acquired by receiving antibodies from another organism

what is natural passive immunity?

immunity acquired by transmission of antibodies from mother to baby