MGD S1 - Cell structure, Amino acids and Proteins

Question 1

Ribosome function?

Answer 1

Ribosomes interpret cellular information from the nucleus and synthesise proteins. There are different types of ribosomes (80s eukaryotic, 70s prokaryotic)

Question 2

Microfilament function?

Answer 2

• Made up of actin
• In non-muscle cells the actin makes up a web-like layer, the cell cortex, located immediately below the cell’s plasma membrane
• The structure helps define the shape of the cell
• They also facilitate the movement of certain particles and structures i.e macrophages, fibroblasts and nerve growth cones

Question 3

Microtubules function?

Answer 3

• Made ups of α-tubulin and β-tubulin dimers
• dynamic structure
• The main ‘building blocks’ forming the cytoskeleton
• The cells framework within which all components of the cell are held in position or allowed restricted movement
• Movement of materials and structures within cells Eg help form the mitotic spindle during prophase

Question 4

Intermediate filament function?

Answer 4

• Important for maintaining the mechanical structure of cells
• There are different types occurring in different cells and therefore provide structural support in slightly different ways

Question 5

Centrosome function?

Answer 5

Contain the centrioles, which are involved in the process of mitosis

Question 6

Nucleus function?

Answer 6

• Control centre of the cell
• Contains cell’s DNA in the form of genes
• Sequestration of DNA and replication of DNA
• Transcription and modification of RNA

Question 7

Rough endoplasmic reticulum function?

Answer 7

• Consists of many interconnected membranous sacs called cisternae, onto which ribosomes are attached In the lumen of the cisternae.

Produce proteins that are either:

1) Retained within vesicles
2) Secreted from the cell

Question 8

Smooth endoplasmic reticulum function?

Answer 8

• Many enzymes attached to the surface of the the cisternae or located within Chemical reactions within the SER vary with the type and location of cells
• Helps with protein folding
• Glycosylation - involves the addition of oligosaccharides
• Disulphide bond formation and rearrangement - to stabilise the tertiary and quaternary structure of many proteins
• Modification of some drugs EG by the cytochrome P450 enzyme in liver cells

Question 9

Lysosome function?

Answer 9

1) Autophagy - Digestion of materials within the cells
2) Heterophagy - Digestion of materials originating from outside the cell
3) Biosynthesis - recycling unwanted products of chemical reactions to process materials received from outside the cell Lysosomes also destroy the cell - usually after it has dies

Question 10

Peroxisome function?

Answer 10

Similar to lysosome but also include:

• β-oxidation of fatty acids
• Breakdown excess purines to urea
• Breakdown of toxic compounds Eg in the cells of the liver and kidney
• Plays a role in the biosynthesis of cholesterol and bile acids derived from cholesterol

Question 11

Vesicle function?

Answer 11

Transport and deliver contents (hormones and neurotransmitters etc) either into or out of the cell, via the cell membrane

Question 12

What are the 4 types of non-covalent interactions that help bring molecules in a cell together?

Answer 12

1) Electrostatic interaction - attractive forces between oppositely charged atoms
2) Hydrogen bonds - special form of polar interaction where an electropositive hydrogen atom is partially shared by two electronegative atoms. It hydrogen can be seen as a proton that has partially disassociated from a donor atom, allowing it to be shared by a second acceptor atom
3) van der Waals attractions - Spontaneous polar interactions
4) Hydrophobic interaction - caused by pushing of non-polar surfaces out of the hydrogen-bonded water network, where they would interfere with the highly favourable interactions between water molecules

Question 13

How many amino acids are there?

Answer 13

20

Question 14

How are amino acids linked?

Answer 14

Covalent peptide bonds

Question 15

Define aliphatic

Answer 15

Hydrocarbons arranged in a linear chain

Question 16

Define aromatic

Answer 16

Closed hydrocarbon chain

Question 17

What is an amphipathic molecule?

Answer 17

Molecule containing both hydrophilic and hydrophobic regions

Question 18

Define pH

Answer 18

Concentration of H+ ions in solution pH= -log(H+)

Question 19

What is the purpose of a buffer?

Answer 19

Solution made of weak acid and its conjugate base that resists changes in pH upon the addition of small amounts of acid or alkali

Question 20

What is the isoelectric point of a protein?

Answer 20

pH at which the protein has no net charge Acidic proteins have a low Pi and basic protein have a high Pi

Question 21

Describe the structure of an amino acid

Answer 21

• Central alpha carbon atom
• Amino group
• Carboxyl group
• R group

Question 22

What happens to an amino acid with a Pi lower than the pH of solution?

Answer 22

Amino acid is deprotonated

Question 23

How are amino acids classified?

Answer 23

Polar, non-polar, aliphatic, aromatic, charged, uncharged

Question 24

Name two non-polar amino acids?

Answer 24

Phenylalanine and Tryptophan

Question 25

Name two negatively charged amino acids

Answer 25

Glutamate and aspartate

Question 26

Name two positively charged amino acids

Answer 26

Lysine and arginine

Question 27

What is a peptide bond? List the features of a peptide bond

Answer 27

• Covalent linking of two amino acids between the carboxyl group of one and the amino group of the other with the subsequent removal of a water molecule
• Peptide bonds are planar, in trans arrangement and have double bond properties due to delocalisation of electrons

Question 28

What is the consequence of a change in the primary structure of a protein?

Answer 28

Altering the sequence of amino acids can impact the secondary and tertiary structure leading to a non-functional polypeptide

Question 29

List the key features of an alpha helix

Answer 29

1) Right handed
2) R groups on the outside of the helix
3) 3.6 amino acids per turn
4) 0.54 nm pitch
5) Stabilised by hydrogen bonds

Question 30

List the key features of a beta pleated sheet

Answer 30

1) Extended conformation
2) Parallel or antiparallel
3) Interconnecting hydrogen bonds between each
4) R groups alternate between opposite sides of the chain
5) 0.35nm pitch

Question 31

Name two helix forming amino acids

Answer 31

Alanine and leucine - small hydrophobic residues

Question 32

Name two helix breaking amino acids

Answer 32

Glycine - Small R groups support other conformation

Proline - non-rotation around C-N bond

Question 33

List the essential amino acids

Answer 33

If Learnt, This Huge List May Prove Truly Valuable

Isoleucine Leucine Tryptophan Histidine Lysine Methionine Phenylalanine Threonine Valine

Question 34

Describe the differences between globular and fibrous proteins and give examples of each

Answer 34

Globular - different secondary structures, compact, for catalysis and regulation Eg enzymes

Fibrous - One type of secondary structure, long strands or sheets, for shape and support Eg collagen

Question 35

What are amyloidosis?

Answer 35

Accumulation of mis-folded or altered dysfunctional proteins which cause disease