Cell structure

Question 1

What is epigenetics?

Answer 1

Control of gene expression by the modification of DNA
Stable, heritable phenotype caused by changes in a chromosome without alterations in DNA sequence
Genes can be switched on/off by internal/external signals

Question 2

What are epigenetics affected by?

Answer 2

Development (during childhood)
Environment
Drugs/Pharmaceuticals
Ageing
Diet

Question 3

Whats a nucleosome?

Answer 3

DNA wound and packed around histone proteins= chromatin

Question 4

Whats a chromosome?

Answer 4

Carries genetic info in the form of genes
Threadlike structure containing nucleic acids and proteins
Found in the nucleus

Question 5

Chromosome structure

Answer 5

Nucleosomes wound together at different levels of superstructure

Question 6

Charge of DNA

Answer 6

-ve

Question 7

Charge of histones

Answer 7

+ve

Question 8

What does DNA’s fractal globule structure mean?

Answer 8

Folded in a way keeping neighbours along NDA helix while remaining completely unknotted

Question 9

How do gene regulatory proteins recognise DNA sequence info?

Answer 9

Outside of NDA double helix is studded with DNA sequence info that gene regulatory proteins can recognise without having to open the double helix

Question 10

What 4 ways can genes be regulated?

Answer 10

1. Transcriptional
2. Post transcriptional
3. Translational
4. Post-translational

Question 11

Transcriptional control

Answer 11

Genes can be turned on/off
Heterochromatin
Euchromatin
- heterochromatin is such part of the chromosomes, which is a firmly packed form and are genetically inactive, while euchromatin is an uncoiled (loosely) packed form of chromatin and are genetically active
Histone modification

Question 12

Heterochromatin

Answer 12

DNA tightly wound around histones= chromatin
Causes chromosomes to be visible during cell division
Transcription of genes not possible as RNA polymerase can’t access the genes
So no transcription during cell division

Question 13

Euchromatin

Answer 13

DNA loosely wound around histones
Present during interphase
So protein synthesis occurs during interphase

Question 14

Histone modification- Acetylation

Answer 14

Acetylation/phosphorylation reduces positive charge on histones
so DNA coils less tightly
allowing certain genes to be transcribed

Question 15

Histone modification- Methylation

Answer 15

Makes histones more hydrophobic
Bind more tightly to DNA
DNA coils more tightly
Preventing transcription of genes

Question 16

Post transcriptional control

Answer 16

RNA processing

RNA editing

Question 17

Post transcriptional- RNA processing

Answer 17

pre-mRNA modified to mRNA
modified nucleotide added to 5’ end
tail of adenine nucleotides added to 3’ end
Helps stabilise mRNA and prevents degradation in cytoplasm
Splicing- introns (non-coding DNA) are removed and exons are joined together
All happens in nucleus

Question 18

Post- transcriptional- RNA editing

Answer 18

Nucleotides of some mRNA sequences can be added/deleted/substituted
Causes proteins to be made with different functions

Question 19

Translational-control

Answer 19

Degradation of mRNA
Binding of inhibitory molecules to mRNA
Activation of initiation factors

Question 20

Translational-control- mRNA degradation

Answer 20

more resistant mRNA= longer it will stay in cytoplasm

so more protein is synthesised

Question 21

Translational control- inhibitory proteins

Answer 21

Inhibitory proteins bind to mRNA
prevents mRNA binding to ribosomes
no protein synthesis

Question 22

Translational control- initiation factors

Answer 22

Initiation factors are activated
help mRNA bind to ribosomes
so more protein synthesis

Question 23

Post translational control

Answer 23

Modifications of proteins:

1. Adding carbohydrate/lipids/phosphates
2. Adding bonds such as disulphide bridges
3. Folding/shortening of protein

Question 24

Role of nuclear envelope in an animal cell@?

Answer 24

Separates chromatin from cytoplasm

Question 25

Peroxisome in animal cell?

Answer 25

Membrane bound organelle

oxidises and breaks down fatty acids

Question 26

Cytoskeleton

Answer 26

Microfilaments- actin
Microtubules- tubulin
Intermediate fibres

Question 27

Function of cytoskeleton

Answer 27

Network of fibres that gives cell stability and structure
Organelle movement
Cell division
Microtubules make spindle fibres for cell division

Question 28

What are centrosomes?

Answer 28

Organelles that produce microtubules

Question 29

Role of cell membrane

Answer 29

Cell compartmentalisation

Endocytosis/exocytosis

Question 30

How do enzymes as biological catalysts help?

Answer 30

1) Greater reaction specificity
2) Function in milder (physiological) reaction conditions
3) Can be regulated
4) They make endpoint more favourable

Question 31

Molecular hierarchy of structure

Answer 31

1. Cells and organelles
2. Chromatin, plasma membrane, cell wall= supramolecular complexes
3. DNA, protein, carbohydrates= macromolecules
4. Amino acids, nucleotides, sugars= monomeric units

Question 32

What is heme?

Answer 32

Organometallic compound

transports O2 in blood

Question 33

What is stereoisomerism?

Answer 33

Molecules have same molecular formula but different spatial arrangement

Question 34

2 types of stereoisomerism?

Answer 34

1. Enantiomerism (optical isomerism)

2. Diastereoisomerism (cis-trans isomerism)

Question 35

Enantiomers

Answer 35

• Form of optical isomerism
• Non superimposable images
• Chiral carbon
• Identical physical properties

Question 36

Diastereoisomers- cis-trans

Answer 36

• E-Z isomerism, E=trans (opposite) , Z= cis (together)
• Have different physical and chemical properties

Question 37

Levels of protein structure

Answer 37

Primary structure- a.a sequence
Secondary structure- folds- alpha helix or beta pleated sheet
Tertiary structure- 3D: polypeptide chains
Quaternary structure- multiple polypeptide chains