Cell Structure (cells) Flashcards
In which cells is the nucleus present
All eukaryotic cells
What is the structure of the nucleus
It is relatively large and separated from the cytoplasm by a double membrane (the nuclear envelope) which has many nuclear pores . These nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus . As well as allowing enzymes to travel in it also contains chromatin and a nucleolus
In which cells is the rough endoplasmic reticulum present
Eukaryotic cells
What is the structure and function of the rough endoplasmic reticulum
Surface covered in ribosomes , formed from continuous folds of membrane continuous with the nuclear envelope. It processes proteins made by the ribosomes
In which cells is the smooth endoplasmic reticulum present
Eukaryotic cells
What is the structure and function of the smooth endoplasmic reticulum
Does not have ribosomes on the surface,it is involved in the production , processing and storage of lipids and carbohydrates
In which cells is the Golgi apparatus present
Eukaryotic cells
What is the structure and function of the Golgi apparatus
Flattened sacs of membrane similar to the smooth endoplasmic reticulum.
It processes proteins and lipids before packing them into the Golgi vesicles (membrane bound sac for transport and storage) the vesicles then transport the proteins and lipids to their required destination eg. Exported out of the cell , put into lysosomes or delivered to other membrane bound organelles
- modifies triglycerides and combines them with proteins packaged for release exocytosis
In which cells is mitocondria present
Eukaryotic ( animal and plant) as too large to fit inside a bacterial cell
What is the structure and function of mitochondria
The site of aerobic respiration,and where ATP is made
surrounded by double membrane , with the inner membrane folded to form Cristae and the matrix formed by the cristae contains enzymes needed for aerobic respiration producing ATP . Also small circular pieces of DNA and ribosomes are also found in the matrix ( needed for replication)
In which cells are chloroplasts present
Plant cells (eukaryotic)
What is the structure and function of chloroplasts
chloroplasts absorb light for photosynthesis and produce carbohydrates/sugars They are surrounded by a double membrane . Have membrane bound compartments , called thylakoids containing chlorophyll stack to form structures called grana (joined together by lamellae- thin and flat thylakoid membranes ) chloroplasts are the site of photosynthesis. They also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis
In which cells are vacuoles present
Present in plant cells ( if present in animal cells , not permanent and small)
What is the structure and function of vacuoles
Holds cell Sap- a dilute fluid consisting of water , amino acids , glucose and salts , and it is surrounded by the tonoplast - a specialised selectively permeable membrane
In which cells are lysosomes present
Animal and plant
What is the structure and function of lysosomes
Specialist forms of vesicles which contain hydrolytic enzymes ( enzymes that break down biological molecules ) and break down waste materials such as worn - out organelles . used extensively by cells of the immune system and in apoptosis ( programmed cell death)
In which cells is the cell wall present
Plant and bacterial
What is the structure and function of the cell wall
Cell walls are formed outside of the cell membrane and offer structural support to cell , this is provided by the polysaccharide cellulose in plants and peptidoglycan (murein) in most bacterial cells
In which cells are ribosomes found
All cells ( eukaryotic and prokaryotic )
What is the structure and function of ribosomes
Found freely in the cytoplasm or as part of the rough endoplasmic reticulum in eukaryotic cells. Each ribosome is a two part complex of ribosomal RNA and proteins . 80S ribosomes (composed of 40S and 60S ) subunits are found in eukaryotic cells . Ribosomes are the sight of translation ( protein synthesis )
In which cells is the cell membrane present
All eukaryotic cells
What is the structure and function of the cell membrane
All cells are surrounded by a cell surface membrane which controls the exchange of materials between the internal cell environment and the external environment . The membrane is described as being partially permeable and is formed from a phospholipid bilayer of phospholipids spanning a diameter of around 10nm
In which cells are centrioles found
Not found in flowering plants or fungi
What is the structure and function of centrioles
Hollow fibres made of microtubules . Two centrioles at right angles to each other form a centro some which organises the spindle fibres during cell division ( mitosis )
What is the smaller knob on the light microscope called
Fine adjustment screw
What is the larger knob on the microscope called
Coarse adjustment screw
What’s the long piece attached to the eyepiece called
Body tube
What are the objective lens called
High power objective lens and low power objective lens
What is the thing below the stage
Condenser
What is the max magnification for a light microscope
X1500
What is the max magnification for an electron microscope
1,000,000
What is the smallest resolution on a light microscope
250 nm
What is the smallest resolution on a electron microscope
0.25nm
What type of radiation is used for a light microscope
Light
What type of radiation is used for an electron microscope
Electrons
How is a light microscope focussed
Glass lenses
How is an electron microscope focussed
Electromagnets
What specimen can be used on a light microscope
Living / moving / dead / abiotic
What type of specimen can be used for an electron microscope
Dead / abiotic
What is the size of a light microscope
Small and portable
What is the size of an electron microscope
Large and static
What is the preparation and cost of light microscopes
Cheap and easy
What is the preparation and cost of material on electron microscope
Large and static
How do light microscopes work
Light microscopes use light and lenses to form to form an image of a specimen and magnify it to look bigger
What is the magnification and resolution of light microscopes
Low
What images do light microscopes give
They give coloured images of cells
Why do light microscopes have a low resolution
Light has a long wavelength
How do electron microscopes work
Electron microscopes use a beam of electrons instead of beams or rays of light
What is the magnification of electron microscopes
High
What is the resolution of electron microscopes and why
High as the electron beam has a very short wavelength
What is an advantage of electron microscopes
They let us see much smaller organelles than light microscopes eg mitocondria
What images do electron microscopes give
Black and white images
What does the specimen have to be to use an electron microscope
Dead
What are the two types of electron microscopes
Transmission electron microscopes (TEM) and scanning electron microscopes (SEM)
How do TEM microscopes work
A microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. Which is focused onto the specimen by a condenser electromagnet. Parts of the specimen absorb electrons ( the denser parts) and therefore appear darker and bright sections where electrons were passed through
What is a limitation of TEM microscopes
Has to be very thin and images formed are in black and white
How does a SEM microscope work
A type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons
What is an advantage of SEM microscopes
The specimens do not need to be as thin as TEM and can show 3D images whereas TEM only show 2D images
Why can the resolving power on TEM microscopes not always be achieved
Difficulties preparing the specimen can limit the resolution and also a higher energy electron beam is required and this may destroy the specimen
What is a limitation of the TEM microscope
Image may contain artefacts
how do you convert mm - um
X1000
magnification =
image size / actual size
What is the definition for cell fractionation
Cell fractionation is the process used to separate cellular components while preserving individual functions of each component.
What are the two stages of cell fractionation
Homogenation and ultracentrifugation
What needs to happen before cell fractionation can begin
Tissue placed in cold , isotonic , buffer solution .
Why is the tissue placed in cold solution
To reduce enzyme activity that might break down organelles
What does isotonic mean
Two solutions ( buffer and tissue ) are at the same concentration
Why is the solution isotonic
Isotonic (same water potential as original tissue) to prevent organelles bursting /shrinking due to osmotic gain/loss os water
Why is the solution buffered
To maintain a constant ph as any change in ph could denature enzymes or alter organelle structure
Describe stage 1 of cell fractionation - homogenation
1) tissue is cut into small peices and placed in a cold , isotonic , buffered solution
2) these are then ground into smaller pieces using a homogeniser which releases the organelles from the cell . The resultant fluid is called the homogenate
3) the homogenate is filtered to remove any complete cells and large debris eg cell wall / membrane
Describe stage 2 - ultracentrifugation
1) ultracentrifugation is the process by which fragments in the filtered homogenate are separated in a machine called a centrifuge
2) the filtrate is placed in the centrifuge and spun at a slow speed
3) the heaviest organelles , the nuclei , are forced (by centrifugal force ) to the bottom of the tube , where they form a thin sediment or pellet .
4) the fluid at the top of the tube (supernatent) is removed , leaving just the sediment behind the nuclei
5) the supernatent is transferred to another tube and spun in the centrifuge at a faster speed
6) the next heaviest organelles the mitocondria are forced to the bottom of the tube
7) the process is continued in this way so that at each increase in speed the next heaviest organelle is separated out
What does homogenise mean
Break down ( tissue )
What is the size order of the organelles
Nucleus -> chloroplasts —> mitocondria -> lysosomes -> endoplasmic reticulum—>ribosomes
What is the supernatent
Remaining organelles (liquid left after centrifugation)
What are the problems with ultracentrifugation
- difficult to separate organelles fully . Other organelles may be present
- cannot separate all organelles
- cannot be sure that the pellet contains one singular organelle
What is the homogenate
The tissue once broken down
What is used to keep it cold
Ice
What is the definition for magnification
Magnification is how many times bigger the image of a specimen observed is in compared to the actual (real - life ) size of the specimen
What is the definition for resolution
A measure of the microscopes ability of to distinguish between two points which are close together on an object
What is the cell cycle
The cell cycle is the series of events that take place in a cell leading to its division to produce two daughter cells.
What is the average time of the cell cycle
A typical human cell might take about 24 hours to divide but fast cycling cells eg the ones that line the intestine can take 9-10 hours this is because they are some of the most hard working cells and need to be replaced rapidly
What are the two stages in the cell cycle
Interphase and mitosis
What is the interphase
A time of organised activity during which the cell synthesises new cell components, such as organelles and membranes and new DNA
What is mitosis
Cell division in body cells
What causes cancer
Uncontrolled cell growth
What percentage of a cells life is spent in interphase
90%
What is a cell checkpoint
To check the cell is working properly . Regulation / check it’s carrying out correct function
What type of cells does chemotherapy target
Cells that go through the cell cycle quickly
What happens at G1. In the interphase
Cell organelles are duplicated - chemical reactions and cell process take place
What happens at s in the interphase
Each of the 46 chromosomes are duplicated
What happens at G2 in the interphase
A period of rapid cell growth and protein synthesis during which the cell readies itself for mitosis . During g2 the cell checks the duplicated chromosomes for errors and duplicates enzymes
what is mitosis
mitosis is the process by which cells divide to achieve growth and repair by simply increasing cell number eg cloning B cells
what is the dividing cell and resulting cells called
the dividing cell is called the parent cell. the resulting two cells are called daughter cells
why are the daughter cells genetically identical
because they contain copies of the parents cells DNA
what is the interphase nucleus
the interphase nucleus looks fairly uniform in images . DNA in interphase is loosely packed - this is called chromatin
what happens to the DNA during mitosis
the nucleus breaks dowbnand the chromosomes condense. chromosomes are made up of DNA associated with proteins called histones
what are the stages in mitosis
prophase , metaphase , anaphase and telophase and cytokinesis
what happens during interphase
the nucleus is in a uniform shape and the chromatin is in its least condensed state. the chromosomes double
what happens during prophase
the nuclear envelope breaks down and the chromosomes begin to appear visible under a microscope due to dna condensing . . organelles known as centrioles migrate towards te poles of the cell to release spindle fibres
what happens when dna doubles
chromatids double and join together at their centres called centromeres they are then called homologous chromosomes
what happens during metaphase
chromosomes are aligned at the cell equator by spindle fibres. this area is called the metaphase plate
what happens during anaphase
the chromatids split at their centromeres and are pulled towards opposite poles of the cell by the spindle fibres
what happens at telophase
nuclear envelopes reform around the two new nuclei . the chromosomes become indistinguisible again under a microscope and the spindle fibres spread out
what happens during cytokinesis
this is the final step of mitosis when the cytoplasm of the parent cell divides to complete the cell division , resulting in two brand new and genetically identical daughter cells . these cells then go through interphase
Describe the role of the spindle during mitosis
Spindle fibres attach to chromatids and then pull chromostids to opposite poles of the cell
Why are viruses described as acellular and non living
They have no cell surface membrane , they have no metabolic reactions and they cannot independently respire or replicate
A student prepared a plant root to observe cells undergoing mitosis . He put the root in a small bottle of hydrochloric acid why
- to soften the cells so soften the root top so the root tip can be more easily squashed . Also stop mitosis / stop mitosis continuting and allowing stain to pass through cells
A student prepared a plant root to observe cells undergoing mitosis . He put the root in a small bottle of hydrochloric acid why
- to soften the cells so soften the root top so the root tip can be more easily squashed . Also stop mitosis / stop mitosis continuting and allowing stain to pass through cells
State two precautions when working with hcl
- eye protection
-gloves
-add water to spills
-do not pour down sink
State two precautions when working with hcl
- eye protection
-gloves
-add water to spills
-do not pour down sink
Describe one difference between SEM and TEM images
3D with SEM and 2D with TEM
What does a colorimeter do
Measures the light absorbance , a calibration curve can be used to draw a line to curve and then read against po2 value obtained
Is po2 pressure or volume
Pressure
do mitocondria contain starch grains
no
name one organelle that you would expect to find in large numbers in a mucus secreting cell and describe its role in the production of mucus
golgi apparatus - packages / processes proteins
or rough endoplasmic reticulum as it makes proteins on ribosomes
give one function of the cell wall
prevents lysis
provides strength and support
protection
describe how tempory mounts are made
place a thin slice of specimen onto a slide and add water and a coverslip
give two reasons why mitosis is important
- replaces cells and tissues
-produces genetically identical cells - cloning
why are chromosomes stained when doing the root tip squash
to distinguish chromosomes / they are not visible without the stain
describe how bacteria divide
they divide by binary fission first - plasmids and circular dna replicate and then the cytoplasm divides producing two daughter cells , each with a single copy of circular dna
how do viruses divide
not living so no cell division , they inject their DNA into a hosts cell and the host cell replicates the virus particles
how does a tumour cause harm to the body
it may exert pressure on other organs or cause obstruction
