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Biology AS > Cell structure 1 > Flashcards

Cell structure 1 Flashcards

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1
Q

What are the characteristics of eukaryotic cells?

A

They have a distinct nucleus.
Membrane-bound organelles.

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2
Q

What is the structure and function of the nucleus?

A

It is usually spherical.
It is between 10 and 20μm in diameter.
It contains the organism’s hereditary material.
It controls the cell’s activities.

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3
Q

What is the structure of the nuclear envelope?

A

It is a double membrane that surrounds the nucleus.
Its outer membrane is continuous with the ER and often has ribosomes on its surface.

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4
Q

What is the function of the nuclear envelope?

A

It controls the entry and exit of materials in and out of the nucleus.
It contains the reactions taking place within the nucleus.

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5
Q

What is the structure of nuclear pores?

A

Typically around 3000 pores in each nucleus.
Each 40 - 100nm in diameter.

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6
Q

What is the function of the nuclear pores?

A

They allow the passage of large molecules (e.g. messenger RNA) out of the nucleus.

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7
Q

What is the structure of the nucleolus?

A

A small, spherical region within the nucleoplasm.
There may be more than one nucleolus in a nucleus

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8
Q

What is the function of the nucleolus?

A

It manufactures ribosomal RNA.

Assembles the ribosomes.

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9
Q

What is the structure of the nucleoplasm?

A

Granular, jelly-like material that makes up the bulk of the nucleus.

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10
Q

What is the structure of chromosomes?

A

Consist of protein-bound, linear DNA.

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11
Q

What are the functions of the nucleus?

A

Acts as a control centre through the production of mRNA and tRNA for protein synthesis.
Retain the genetic material of the cell in the form of DNA and chromosomes.
Manufacture ribosomal RNA and ribsomes.

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12
Q

What is the structure of the mitochondria?

A

Usually rod-shaped.
1 - 10μm in length.
Contain a double membrane, cristae, and matrix.

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13
Q

What is the function of the double membrane of the mitochondria?

A

It is around the organelle.
It controls the entry and exit of material.
The inner of the two membranes is folded to form extensions (cristae).

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14
Q

What are the cristae?

A

Extensions of the inner membrane.
They provide a large surface area for the attachment of enzymes and other proteins involved in respiration.

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15
Q

What is the matrix?

A

Makes up the remainder of the mitochondria.
Contains lipids, proteins, ribosomes and DNA. This allows the mitochondria to control the production of its own proteins.
Many enzymes involved in respiration are found in the matrix.

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16
Q

What is the function of the mitochondria?

A

It is the site of aerobic respiration.

It produces ATP, from respiration.

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17
Q

What is the function of chloroplasts?

A

They harvest sunlight.

The site of photosynthesis.

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18
Q

What is the structure of chloroplasts?

A

Typically disc-shaped

2-10μm long and 1μm in diameter.

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19
Q

What is the chloroplast envelope?

A

A double plasma membrane that surrounds the organelle.
It is highly selective in what it allows to enter and exit the chloroplast.

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20
Q

What is the grana?

A

They are stacks of up to 100 disc-like structures called thylakoids.
The first stage of photosynthesis (light absorption) takes place here.

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21
Q

What are thylakoids?

A

Contain the photosynthesis pigment chlorophyll.
Some thylakoids have tubular extensions that join up with thylakoids in adjacent grana.

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22
Q

What are the stroma?

A

A fluid-filled matrix where the second stage of photosynthesis (synthesis of sugars) takes place.
Contain starch grains and other structures.

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23
Q

How are the granal membranes adapted to their function?

A

They provide a large surface area for the attachment of chlorphyll, electron carriers and enzymes that carry out stage 1 of photosynthesis. These chemicals are attached to the membrane in a highly ordered fashion.

24
Q

How are the stroma adapted to their function?

A

The fluid of the stroma possesses all the enzymes needed to make sugars in stage 2 of photosynthesis.

25
Q

How are chloroplasts adapted to their function?

A

Chloroplasts contain both DNA and ribsomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis.

26
Q

What is the Endoplasmic Reticulum?

A

Three-dimensional system of sheet-like membranes, spreading through the cytoplasm of cells.
It is continuous with the outer nuclear membrane.
The membranes enclose a network of tubules and flattened sacs called cisternae.

27
Q

What is structure of the Rough Endoplasmic Reticulum?

A

It has ribosomes present on the outer surfaces of the membranes.

28
Q

What is the function of the RER?

A

Provides a large surface area for protein and glycoprotein synthesis.
Provides a pathway for the transport of materials (especially proteins) throughout the cell.

29
Q

What is the structure of Smooth Endoplasmic Reticulum?

A

It lacks ribosomes on its surface.
It is often more tubular in appearance.

30
Q

What are the functions of the SER?

A

Synthesise, store and transport lipids and carbohydrates.

31
Q

What are the functions of the Golgi apparatus?

A

Add carbohydrate to proteins to form glycoproteins.
Produce secretory enzymes.
Secrete carbohydrates.
Transport, modify and store lipids.
Form lysosomes.

32
Q

What is the structure of the Golgi apparatus?

A

Similar to the SER, except more compact.
It consists of a stack of membranes that make up flattened sacs called cisternae with vesicles.

33
Q

What does the golgi apparatus do?

A

The proteins and lipids produced by the ER pass through the golgi apparatus in strict sequence.
The Golgi modifies these by adding non-protein components, e.g. carbohydrates, to them.
It also allows them to be accurately sorted and sent to the correct destinations.
It then packages them into vesicles to be transported to the cell surface, where they fuse with the membrane and release their contents to the outside.

34
Q

What are lysosomes?

A

They are formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases.

35
Q

What are ribosomes?

A

Small cytoplasmic granules found in all cells.
Found in the cytoplasm or associated with the RER.

36
Q

What are 80S ribosomes?

A

Found in eukaryotic cells.

They are around 25nm in diameter.

37
Q

What are 70S ribosomes?

A

Found in prokaryotic cells, mitochondria and chloroplasts.
Slightly smaller than 80S, (<25nm).

38
Q

What is the structure of ribosomes?

A

They have 2 subunits - one large and one small.
They each contain ribosomal RNA and protein.
Despite their small size, they occur in vast numbers so they make up 25% of the dry mass of a cell.

39
Q

What is the function of ribosomes?

A

The site of protein synthesis, which acts as an assembly line to use RNA to assemble proteins.

40
Q

What is the structure of cell walls?

A

Consist of a number of polysaccharides such as cellulose.
There is a thin layer called the middle lamella - it marks the boundary between adjacent cell walls and cements them together.

41
Q

What is the function of cell walls?

A

Provides mechanical strength to prevent the cell bursting under pressure by osmotic entry of water.
The cellulose provides mechanical strength to the whole cell.
Allow water to pass along it - so it contributes to the movement of water throughout the plant.

42
Q

What is the structure of vacuoles?

A

A fluid-filled sac bound by a single membrane - tonoplast.

43
Q

What is the function of vacuoles?

A

Contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments, e.g. anthocyanins.
The sugars and amino acids may act as a temporary food store.
Provide support to the plant by making it turgid.
The pigment may colour petals to attract pollinating insects.

44
Q

What are the functions of lysosomes?

A

Hydrolyse material ingested by phagocytic cells, such as white blood cells and bacteria.
Release enzymes to the outside of the cell (exocytosis) to destroy material around the cell.
Digest worn out organelles so the useful chemicals they’re made from can be re-used.
Completely break down dead cells (autolysis).

45
Q

What are lysozymes?

A

Enzymes that hydrolyse the cell walls of certain bacteria.

46
Q

What is the structure of lysosomes?

A

They contain lysozymes.
As many as 50 enzymes can be contained in a single lysosome.
Up to 1μm in diameter.

47
Q

What are the characteristics of prokaryotic cells?

A

They are smaller than eukaryotes.

Have no nucleus or nuclear envelope.

48
Q

What is the size of bacteria?

A

Range from 0.1 - 10μm in length.

49
Q

What is the capsule? (prokaryotic cells)

A

A capsule of mucilaginous slime is secreted around the cell wall.
It protects bacterium from other cells and helps groups of bacteria to stick together for further protection.

50
Q

What is the cell wall? (prokaryotes)

A

Made of murein
Physical barrier that excludes certain substances and protects against mechanical damage and osmotic lysis.
10 - 80nm thick.

51
Q

What is the cell-surface membrane? (prokaryotes)

A

Acts as a differentially permeable layer, which controls the entry and exit of chemicals.
It is inside the cell wall.

52
Q

What is circular DNA?

A

Possesses the genetic information for the replication of bacterial cells.

53
Q

What are plasmids?

A

They possess genes that may aid the survival of bacteria in adverse conditions (e.g. produce enzymes that break down antibiotics).
Circular pieces of DNA.

54
Q

What are the flagella?

A

Used for locomotion.
Only found in some species of prokaryotic cells.

55
Q

What is the pili?

A

Some prokaryotic species have pili.
They are used to adhere to other cells.

56
Q

Compare prokaryotic and eukaryotic cells.

A

No true nucleus, only an area where DNA is found.
- distinct nucleus and a nuclear envelope.
DNA not associated with proteins.
- DNA associated with proteins called histones.
Some DNA is in the form of plasmids.
- no plasmids and DNA is linear.
No membrane-bound organelles
- membrane-bound organelles.
Ribosomes are smaller [70S]
- ribosomes are larger [80S]
Cell wall made of murein.
- cell wall made of cellulose.
May have a capsule
- no capsule.

57
Q

What are viruses?

A

Acellular, non-living particles.
Range in size from 20-300nm, smaller than bacteria.
Contain nucleic acids such as DNA or RNA as genetic material but can only multiply inside living host cells.
Nucleic acid is enclosed in a protein coat called a capsid.
Some have a lipid envelope - has attachment proteins which are essential in allowing the virus to identify and attach to host cells.

Biology AS (20 decks)

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