Chapter 3 - Cell Structure Flashcards
What is a eukaryotic cell?
Defined as cells that contain membrane bound organelles.
Describe the structure and function of the nucleus.
- Has a nuclear envelop - double membrane that surrounds it.
- Has nuclear pores - allow molecules (ribosomes/mRNA) out
- Nucleolus - where ribosomal RNA is made
- contains DNA which codes for protein synthesis
- site of DNA REPLICATION in eukaryotes.
- histone proteins: wrap linear DNA around these to make chromosomes.
RIBOSOMES
What are they made of, what are they used for and is there size differences?
- made of ribosomal RNA and protein - assembled in nucleolus
- HAVE NO MEMBRANE
- used for protein synthesis
- ribosomes in eukaryotes are LARGER than in prokaryotes.
How are ribosomes made? [4]
- Nucleolus makes ribosomal RNA
- Ribosomal proteins are made in cytoplasm, then imported into nucleus
- Nucleolus then assembles complete ribosomes using protein and ribosomal RNA
- The completed ribosomes then move from the nucleus into the cytoplasm via nuclear pores.
- some attach to endoplasmic reticulum, others remain free in cytoplasm
Describe the structure and functions of the rough endoplasmic reticulum
- consists of membrane - bound flattened sacs called cisternae
rER:
1. Has ribosomes on outer surface
2. transports proteins made by ribosomes
3. Present in large amounts of cells that make enzymes that may be secreted out of the cell.
- Name the structure that the smooth endoplasmic reticulum doesn’t have
- What does the sER do?
- Has membranes that LACK ribosomes
- assist in the synthesis and transport of lipids
Describe the process of protein secretion. [7]
- DNA in nucleus codes for a protein
- Ribosomes on rER produce protein
- Mitochondria produce ATP for this protein synthesis
- Vesicles bud off the rER and transport the protein to the Golgi apparatus
- The Golgi apparatus MODIFIES the protein (add carbohydrate to make glycoprotein)
- Vesicles then bud off the Golgi apparatus, carrying the protein to the cell surface membrane
- The vesicles FUSE with the cell surface membrane, releasing their protein contents to the outside of the cell
- Where will the protein be made if it is going to end up in the cell cytoplasm
AND
- Where will it be made if going to be transported to the Golgi apparatus?
- Made by the ribosomes free in cytoplasm
- Made by ribosomes bound to rER
Describe the structure and function of the Golgi apparatus
Also mention about Golgi vesicles.
Golgi apparatus: stack of flattened sacs = cisternae
- Enzymes + proteins packaged into Golgi vesicles for secretion
- Some combined with carbohydrate to form glycoproteins
- Work in transporting and storing lipids
- Form lysosomes
Describe what lysosomes are, what they contain and what these do.
- they are a special type of Golgi vesicle
- contain LYSOZYMES that are enzymes which carry out hydrolysis.
- Lysozymes can be used to digest worn out organelles, digest food particles taken up by phagocytosis
- white blood cells (phagocytes) use lysozymes to digest pathogens.
Describe the function of mitochondria and it structure.
- produces ATP via aerobic respiration = energy for many cell processes
- has folds called cristae which provide a large SA to hold proteins involved in aerobic respiration
- the matrix (fluid filling the mitochondria) contains enzymes for aerobic respiration.
EXAM TECHNIQUE
Why do some mitochondria look different under a microscope?
They have been cut in different planes
What is the word equation for photosynthesis?
Carbon dioxide + water —> oxygen + glucose
PLANTS ONLY
Describe the structure of chloroplasts.
- surrounded by double membrane = envelope
- contain thylakoids - contain chlorophyll which absorbs light energy
- thylakoids stack up into grana
- some of the glucose gets stored up as starch grains
- has stroma = fluid that fills chloroplast (contains enzymes for photosynthesis)
PLANTS ONLY
Describe the function of chloroplast
- site of photosynthesis - absorb light energy to make sugar
PLANTS ONLY
What is the cell wall made of
Cellulose
Describe the functions of the cell wall. [3]
- Provides mechanical strength to prevent OSMOTIC LYSIS
- Provides mechanical strength to plant as a whole
- Permeable to water so allows water to travel through the plant
What is different about the cell walls of fungi?
Possess cell walls made of a polymer called chitin - not plants so do not photosynthesise
PLANTS ONLY
What is the cell vacuole?
Large, permanent fluid filled sac surrounded by a single membrane called a TONOPLAST
PLANTS ONLY
Describe the functions of the cell vacuole [3]
- inflates with water to make cells turgid
- Stores sugar and amino acids as food
- Contain pigments to colour petals of flowers and therefore attract insects for pollination
How is a prokaryotic cell different to eukaryotic cells? [5]
- much smaller
- no membrane bound organelles
- smaller ribosomes
- no nucleus - instead have single circular DNA molecule free in cytoplasm that is not associated with histones
- a cell wall that contains MUREIN = a glycoprotein.
E.g. BACTERIA
What are some other things that prokaryotes have? [3]
- plasmids: small circular piece of DNA
- capsule around cell: mucilaginous layer of slime
- flagella: used for locomotion
Why might have mitochondria and chloroplast evolved from free living bacteria?
- contain circular DNA
- contain smaller ribosomes
(Both features are shared with bacteria)
What are the 2 key things about viruses?
What are the 3 key structures on a virus?
- acellular (not made of cells) and non living
- Genetic material: can be DNA or RNA
- Capsid: made of proteins and contains genetic material
- Attachment proteins: help the virus identify and attach to host cell
What does the term resolution refer to?
- a measure of the ability of a microscope to distinguish detail
E.g. the minimum distance at which two distinct points of a specimen can still be seen as SEPARATE ENTITIES
Which microscope has a better resolution, optical or electron and why?
Electron has better resolution because:
- a beam of electrons has a shorter wavelength than light
What are the differences between electron and optical microscopes? [7]
- ELECTRON uses electrons whereas OPTICAL uses light.
- ELECTRON has greater resolution whereas OPTICAL has lower resolution
- SO… ELECTRON can observe smaller organelles in more details whereas OPTICAL can only observe larger organelles in less detail
- In ELECTRON the specimen has to be dead whereas OPTICAL can use living or dead
- ELECTRON does not show colour whereas OPTICAL can show colour
- ELECTRON prep is more complex and more time consuming whereas OPTICAL is less complex and time consuming
- ELECTRON focuses using magnets whereas OPTICAL focuses using glass lenses
How would you mount a specimen for the optical microscope? [3]
- Take a thin slice/ section;
- Put on slide and add stain as required;
- Add cover slip using a mounted needle;
Why must electron microscope specimens be dead?
- electron microscopes must use a vacuum (completely empty space) to ensure the electron beam isn’t disrupted
- vacuum would kill any specimen
What stops electron microscopes achieving max resolution?
- Changes to specimen during prep can limit resolution
- Higher energy electron beams give even greater resolution, but can damage specimen
What are the two types of electron microscopes and what’s the differences?
- Transmission electron microscope:
- very thin specimen
- electron beam passed through specimen
- 2D image at BEST RESOLUTION
- Scanning electron microscope:
- thicker specimen
- electron beam scans across specimen and is scattered off the surface of sample
- pattern of scatter used to determine 3D shape of sample
- resolution not so good
How would you measure the size of an object viewed with an optical microscope?
- Measure structure using eyepiece graticule;
- Calibrate eyepiece graticule against stage micrometer;
- Take a number of measurements to calculate mean;
What is the formula for magnification?
Magnification = size of image / size of real object
What is an artefact?
When a specimen is damaged during preparation
Describe how you would carry out cell fractionation and ultracentrifugation.
- Chop up fresh liver tissue in ice-cold isotonic buffer solution
- Put tissue in homogeniser (blender) to break open cells and release organelles
- Filter mixture to remove debris
- Spin mixture in a centrifuge so that denser parts get moved to the bottom forming a bullet
- The supernatant is poured into a tube leaving a sediment (which contains nuclei)
- Supernatent can then be spun again at a faster speed to produce a sediment containing LESS DENSE organelles etc.
What are the 3 stages of centrifugation? List the organelles that are filtered out at each one.
- Spun at low speed = more dense = nuclei
- Spun at medium speed = bit less dense = mitochondria
- Spun at high speed = least dense = ribsomes
What are the conditions for homogenisation solution and what do they do?
- ICE COLD - slows/ stops enzyme activity to prevent digestion of organelles
- BUFFERED - maintains pH so that enzymes/ other proteins are not denatured
- ISOTONIC - same water potential prevents osmosis so no lysis/ shrinkage of organelles
How is eukaryotic DNA packaged?
- packaged into chromosomes
DNA + HISTONE PROTEINS = CHROMATIN
Stage 1 of mitosis:
What occurs during prophase?
- chromosomes condense;
- chromosomes appear as 2 sister chromatids joined at the centromere;
- nuclear envelope breaks down;
Stage 2 of mitosis:
What occurs during metaphase?
- chromosomes line up on the equator/ centre of the cell;
- chromosomes attached to spindle fibres by their centromere;
Stage 3 of mitosis:
What occurs during anaphase?
- the centromere splits;
- sister chromatids, now chromosomes, are pulled to opposite poles of the cell by the SHORTENING of the spindle fibres;
Stage 4 of mitosis:
What occurs during telophase?
- chromosomes uncoil and de-condense;
- nuclear envelop reforms around each group of chromosomes;
What occurs during cytokinesis?
- cytoplasm divides producing two genetically identical daughter cells.
Why is mitosis important?
- Increases cell number to allow growth;
- Replace cells to allow repair of tissues;
- Produces genetically identical cells;
- Can sometimes allow asexual reproduction;
How do prokaryotic cells divide and what does it involve?
Use binary fission:
- Replication of circular DNA and of plasmids
- Division of cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of plasmids.
