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Alevel Biology > Cell Biology > Flashcards

Cell Biology Flashcards

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1
Q

Electron microscope

A

The use electrons to create a magnified image of the sample.

The specimen also has to de dead as the sample is put into a vacuum to be magnified.

have higher resolving power. This means that we can study cells in much finer detail. This has enabled biologists to see and understand many more sub celular structures.

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2
Q

Describe the principle on the limitation of using a transmission electron microscope to investigate cell stricture

A

Principles: electrons pass through/enter thin specimen. Denser parts absorb more electrons. So denser parts seem darker. Electrons have a short wavelength so give a higher resolution.
Limitations: cannot look at living material must be in a vacuum. Specimen must be very thin. Artefacts present. Complex staining method long prep time. Image not in 3D only 2D images are produced.

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3
Q

Artefacts

A

• An artefact is things that aren’t meant to be in the microscope sample that are not part of the specimen.
• Examples of artefacts include dust, air pockets and/or halos. Artefacts are usually created when preparing the specimen.
• Artefacts are common in electron microscopes due to the difficulty and the time it takes to set up which creates lots of opportunities to mess up.

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4
Q

Magnification and scale

A

long wavelength means that light microscopes can only distinguish between objects if they are 0.2 micrometers or further apart.
This limitation can be overcome by using beams of electrons rather than beams of light.
With their shorter wavelength, beams of electrons can distinguish between 2 objects as close as 0.1 nanometers.

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5
Q

scanning electron microscopes (SEM)

A

In scanning electron microscopes (SEM) electrons are scattered by surface contour of the specimen producing a 3D image.
Density in images - more electrons attract and absorbed because the subject is more dense meaning it is darker. This is the same in light microscopes as well.

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6
Q

DNA in eukaryotes

A

the DNA is contained in nucleus. Their DNA is tightly wrapped around proteins called histones.
Together the DNA and histone proteins form chromosomes.
Their DNA is a linear molecule, meaning the ends are not joined together to form a loop.

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7
Q

What are the main 3 uses of protein

A

• Enzymes for chemical reactions
• Structural proteins eg organelle movement.
• Transport molecules eg haemoglobin.

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8
Q

Synthesising proteins

A

The instructions for encoding the amino acid sequence of a protein are in the gene of that protein, these are part of the chromosomes in the nucleus.

the genetic info coded by that gene is converted to mRNA (transcription) this mRNA leaves the nucleus to carry out translation

Some proteins are secreted from cells. They are translated on a ribosome attached to the rough endoplasmic. The proteins make their way through the ER and the Golgi apparatus.

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9
Q

What is the nucleoplasm

A

The nucleus contains a material called the nucleoplasm. The nucleoplasm contains molecules such as nucleotides and enzymes.

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10
Q

What is the nuclear envelope

A

there is a double membrane called the nuclear envelope. The nuclear envelope consists of two phospholipid bilayers. There are also nuclear pores, which allow molecules to enter and leave the nucleus.

The outer membrane with the nuclear envelope is continuous with the rough endoplasmic reticulum, which plays a role in protein synthesis.

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11
Q

What is chromatin

A

Nucleus also contains chromatin, which consists of DNA coiled around proteins called histones, the DNA and histone proteins form chromosomes. Chromosomes are not visible in the nucleus unless the cell is undergoing mitosis or meiosis.

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12
Q

What is the nuclelolus.

A

Inside the nucleus on an electron micrograph, the region that is darker than the rest is called the nuclelolus.

This is where a special type of rRNA. Ribosomal RNA forms the structure of ribosomes. The nucleolus is also where the ribosome subunits are assembled.

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13
Q

The rough endoplasmic reticulum

A

A large number of ribosomes are attached to the rough endoplasmic reticulum.

The rough ER consists of sheets of membranes forming flattened sacs called cisternae which contain a range of enzymes. The membrane of cisternae are covered with ribosomes.

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14
Q

What happens when a polypeptide chain passes into the lumen of the rough er

A

This is where the chain folds into its tertiary structure. Now, it makes its way through the rough ER. During the process, the polypeptide can be modified.

The polypeptide is packaged into vesicles and transported into the golgi apparatus

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15
Q

Endocytosis and exocytosis

A

Endocytosis - entering the lumen of the rough ER
Exocytosis - exiting the lumen of the rough ER

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16
Q

Smooth endoplasmic reticulum

A

Cells that secrete large amounts of protein will have a lot of RER. Some rer are not covered in ribosomes this is called smooth endoplasmic reticulum. The job of the smooth ER is to make and store both lipids and carbohydrates.

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17
Q

What is the function of the golgi apparatus

A

The golgi apparatus consists of sheets of flattened sacs (folded membranes) called cisternae. As the polypeptide makes its way through the golgi apparatus it can be modified further. Here the polypeptide will reach its final structure so it can be referred to as a functional protein.

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18
Q

What happens when the protein passes through the golgi

A

Once the protein has travelled through the golgi apparatus, it is packaged into vesicles. These vesicles can then fuse with the cell membrane and the protein can be secreted from the cell. Or the protein can form part of the cell membrane or go on to form lysosomes.

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19
Q

Roles of lysosome

A

• Contain the enzyme lysozyme and protease digest and break down bacteria
• Can be dangerous if they’re in the wrong place
• Can also destroy cells that are damaged or no longer functional.
• Internal fluid of a lysosome is acidic.
• Contains a lot of cholestrol to make it have a thick membrane

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20
Q

What are mitochondria key for

A

Key for aerobic respiration to produce the energy carrying molecule ATP. In respiration, the energy contained in the chemical bonds of glucose, is transferred to ATP.

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21
Q

Two stages of repsiration

A
  1. Glycolysis - takes place in cytoplasm
  2. The Krebs Cycle and oxidative phosphorylation (requires oxygen) - in the mitochondria
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22
Q

Membranes in mitochondria

A

Mitochondria have a double membrane - the outer membrane and the inner membrane. In between the membranes is called the inter membrane space.

There are also enzymes on the inner membrane which has a large surface area.

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23
Q

Matrix

A

Within the mitochondria there is a fluid called the matrix.
The enzymes for the kreb cycle are found in the matrix (liquid inside mitochondria).

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24
Q

What is a chloroplast surrounded by

A

Chloroplasts are surrounded by a double membrane.

25
Q

What are thylakoids

A

The membrane bound flattened disks are called thylakoids, this is where the light dependant reactions take place so contain chlorophyll and enzymes.

26
Q

What are stacked thylakoids called

A

These discs stacked are called granum, by stacking them, light can be absorbed more efficiently. When the discs are stacked, they are connected by a flattened membrane called lamelllae.

27
Q

Liquid in chlorplasts

A

Chloroplasts contain a liquid called stroma, this is where the light independent reactions take place so contains enzymes.

28
Q

What else is in chloroplats

A

Starch granules are also contained in the chloroplasts as a product of photosynthesis.
Chloroplasts contain a loop of DNA which contains genes which encode for some proteins. And they also contain ribosomes to synthesise protei

29
Q

Reactions in chloroplast

A

The energy trapped in photosynthesis is contained within the chemical bonds in the glucose molecule.
The light dependant reactions use chlorophyll to harvest light energy. The energy is then transferred to the other molecules.
Light independent reactions take place in both light and dark conditions.

30
Q

Comparing prokarys to eukarys

A
  1. Prokaryotic cells are much smaller than eukaryotic cells
  2. No membrane bound organelles, DNA is found in cytoplasm so DNA is in a circular chromosome with no free ends.
  3. The DNA in prokaryotes is not bound to histone proteins
  4. Bacterial cells can contain small loops of DNA called plasmids which contain a relatively small number of genes but these can include genes which make bacteria resistant to antibiotics.
31
Q

Cell walls in rpokaryot

A

Prokaryotic cells are surrounded by a cell wall, in bacteria this is called peptidoglycan which is also called murein. This is a polymer formed between peptides and polysaccharide molecules.the cell wall helps maintain the structure of the cell.

32
Q

What is the flagellum

A

Flagellum - helps the cell move. The prokaryotic flagellum has a different structure to the ones found in eukaryotes.

33
Q

What is pili

A

Some bacteria also have fine protein strands on their surface called pili. This helps bacteria attatched to surfaces and other bacteria.

34
Q

What is a mesosome

A

Mesosomes - infoldings in the cell membrane of prokaryotic cells. An example of an artefact when bacterial cells are prepared for electon microscopy

35
Q

What is the nutrient stores for bacterial cell

A

Bacteria also contain lipid droplets and glycogen granules. Whcih act as nutrient stores for the bacteria cell.

36
Q

What is the cell wall made of

A

Made of polysaccharide cellulose which is a polymer betaglucose.cellulose molecules can form hydrogen bonds forming larger structures called microfibrils which is extremely strong. Provides strength to the cell. Controls osmosis to prevent bursting.

37
Q

What is between cell walls

A

a layer called the middle lamella, which is a layer of polysaccharides aswell as calcium and magnesium ions. The function of this is to act as a glue between plant cells.

38
Q

Cell walls in algae and fungi

A

In algae the cell walls can contain both cellulose and glycoprotein whereas in fungi the cell wall are made of polysaccharide kytin aswell as others and glycoprotein.

39
Q

Genetic material in viruses

A

All viruses contain genetic material (DNA or RNA). The genetic material is contained inside a protein structure called a capsid. On the surface there are attachment proteins, these allow the virus particle to attach and enter the host cell.

40
Q

How do viruses reproduce

A

Many viruses are broadly spherical. Viruses cannot reproduce independently, can only reproduce inside of a host cell where it can use the host cells enzymes to copy itself. Viruses are acellular meaning not based on cells. They are not counted as living organisms.

41
Q

What is the plant cell vacuole surrounded by

A

A plant cell vacuole is surrounded by a membrane called the tonoplast. This controls which chemicals enter and leave the vacuole.

42
Q

Cell sap

A

The fluid in the vacuole is called the cell sap. Cell sap contains disolved sugars, mineral salts and amino acids.

The cell sap has low water potential, this means water moves into the plant by osmosis and that water enters the vacuole. This creates a hydrostatic pressure acting outwards. Causing cytoplasm to press against the cellulose cell wall.

43
Q

Vesicles and large vacuoles

A

Vesicles - sacs of fluid enclosed by a membrane.
Larger and longer living vesicles are called vacuoles so can transport/carry other molecules.

They also are key in the removal of waste materials.
Animal cell vacuoles are temporary structures, however in plant cells there is a larger permanent vacuole.

44
Q

Plasma membranes

A

Cell membranes control exit and entry to the cell. Plasma membranes cover the surface of every cell and surround most organelles within the cell.

45
Q

Several functions of the plasma membranes

A
  1. Keeping all cellular components inside the cell
  2. Allowing selected molecules in and out of the cell
  3. Isolating the organelles from the rest of the cytoplasm allowing cellular processes to occur separately
  4. Allows cell to change shape eg red blood cells
46
Q

Phospholipids in plasma membranes

A

Phospholipids are the basic components of a plasma membrane. Phospholipids contain a polar hydrophilic phosphate head and non-polar hydrophobic tails.

When exposed to water, phospholipids form one of two structures: a MONOLAYER or a MICELLE. A monolayer can form at a water/air interface however in living cells, these are rare. Phospholipids also form a bilayer.

47
Q

Phospholipids in plasma membranes

A

Phospholipids are the basic components of a plasma membrane. Phospholipids contain a polar hydrophilic phosphate head and non-polar hydrophobic tails.

When exposed to water, phospholipids form one of two structures: a MONOLAYER or a MICELLE. A monolayer can form at a water/air interface however in living cells, these are rare. Phospholipids also form a bilayer.

48
Q

What are glycoproteins

A

• Chains of carbohydrates attached to proteins.
• They are the receptors (carbohydrate components extend outside the cell)

49
Q

Functions of gylcoprotein:

A

Functions:
Recognition sites for hormones and neurotransmitters
Allows cells to recognise each other (ie lymphocites can recognise body’s own cells)
Helps cells attach to each other to form tissues

50
Q

Cholestrol

A

• Cholesterol molecules provide strength to membranes
• They are very hydrophobic, they prevent water loss and loss of ions from the cell
• They limit the movement of phospholipids by attracting the tails, this allows them to have some flexibility.

51
Q

Cholestrol

A

• Cholesterol molecules provide strength to membranes
• They are very hydrophobic, they prevent water loss and loss of ions from the cell
• They limit the movement of phospholipids by attracting the tails, this allows them to have some flexibility.

52
Q

Functions of cholestrol:

A

Reduce the fluidity at high temperatures and too rigid under cool conditions
Supposed to stop lateral movement.
Increases the strength of the cell surface membrane

53
Q

Fluid mosaic model name

A

“Fluid” used because phospholipid molecules can move around each other meaning membrane is flexible and can change shape. “Mosaic because the membrane is studded with protein molecules and the arrangement of these proteins vary.

54
Q

Functions of membranes in cells

A
  1. Act as barriers eg between internal contents of cell and the external environments.
  2. Membranes separate parts of organelles
  3. Membranes can also be a location for chemical reactions
  4. Membranes are involved in cell signalling.
55
Q

Hydrophobic center in membranes

A

The hydrophobic center prevents water-soluble molecules from easily passing through. This is because hydrophilic substances are polar (have a charge), these substances cannot easily pass through the non-polar region of the membrane.

Water molecules can pass through because they are extremely small.

The cell-surface membrane is based on the phospholipid bilayer. The cell surface membrane contains a large number of protein molecules.

56
Q

Intrinsic protein

A
  • protein that spans the whole length of the bilayer. It contains a channel/carrier in the center of the protein where molecules can pass through the gap, it is lined with hydrophilic amino acids and is filled with water molecules. Carrier proteins are another example that can change their shape or position to transfer from one side of the membrane to the other. They have hydrophobic amino acids on the outside surface of the protein. These can interact with the hydrophobic tails in the bilayer
57
Q

Partially Intrinsic protein -

A

Only spans through half of the bilayer. As it cant pass through the bilayer it cannot be used for transport.

58
Q

Partially Intrinsic protein -

A

Only spans through half of the bilayer. As it cant pass through the bilayer it cannot be used for transport.

59
Q

Glycolipids

A

Glycolipids - carbohydrates that are found attached to phospholipid molecules. Often used when cells come into contact with each other. The glycolipids on the surface of one cell can be recognised by another cell. Can also act as antigens for example determining blood group.

Alevel Biology (6 decks)

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