Cell physiology

Question 1

What gives cells their overall negative charge?

Answer 1

Carbohydrates on cell membrane causing a loose carbohydrate coat - glycocalyx

Question 2

What is ATP made up of?

Answer 2

Adenosine, ribose, 3 phosphate radicals joined by high energy phosphate bonds

Question 3

What is the function of non-motile/primary cilia? How does their structure differ to motile cilia?

Answer 3

Non-motile cilia have only a single cilia which acts as an antenna - sensory.

Motile ciliated cells have thousands of cilia

Question 4

What are the 2 ways by which endocytosis can occur?

Answer 4

1. Pinocytosis - this is ingestion of minute particles. Particle attaches to cell membrane receptor which are concentrated in coated pits on the cell membrane. Beneath these coated pits is a lattice of clarithrin +/- actin/myosin which contract to invaginate the pit inwards. Requires ATP.
2. Similar to pinocytosis but only specialised cells can do this, for ingestion of larger particles.

Question 5

After endocytosis, what happens to the particles that have been ingested?

Answer 5

Lysosomes bind to the vesicle to digest it - these lysosomes contain bactericidal material (e.g. lysosyme) and lysoferrin (to bind iron) to inhibit bacteria.

Products of digestion diffuse into cytoplasm.

Leaves a residual body in the vesicle which is excreted by exocytosis

Question 6

What is the function of the endoplasmic reticulum?

Answer 6

Rough - protein synthesis with ribosomes

Smooth - lipid synthesis to be incorporated into lipid bilayer

Question 7

What is the function of the Golgi apparatus?

Answer 7

Makes certain carbohydrates that can’t be made by the ER - e.g. large polysaccharide molecules

Forms secretory vesicles

High numbers in glandular cells on side of secretion

Question 8

What makes up the cell cytoskeleton and where are these made?

Answer 8

Made up of fibrillar proteins which are made by ribosomes of the ER - strong and ropelike filaments

Question 9

What makes up a nucleotide?

Answer 9

Phosphoric acid
Deoxyribose
One nitrogenous base

Question 10

What are the 4 nitrogenous bases in DNA and which ones pair together?

Answer 10

Purines - adenine and guanine
Pyrimidines - thymine and cytosine

A and T go together
G and C go together

Question 11

What holds nitrogenous base pairs together? How many bonds between each base?

Answer 11

Loose hydrogen bonds

2 bonds between A and T
3 bonds between G and C

Question 12

What is codon?

Answer 12

Group of 3 bases

Question 13

What is transcription?

Answer 13

Transfer of DNA code to RNA code

Question 14

What are 2 differences between DNA and RNA nucleotides?

Answer 14

1. Rather than thymine - URACIL
2. Rather than deoxyribose - RIBOSE

Question 15

What does RNA polymerase do? What causes RNA polymerase to start and stop?

Answer 15

Attaches to promoted gene = sequence of base pairs just before gene to be transcribed
Attaching of RNA polymerase to DNA promoter causes DNA to unwind
RNA polymerase then moves along DNA strand and transcribes
Stopped by a chain terminating sequence

Question 16

What is mRNA and what is its function?

Answer 16

Messenger RNA - takes DNA code from nucleus into cytoplasm to be used for protein synthesis

Question 17

What is the function of transfer RNA? What is its shape?

Answer 17

Carries amino acids to the ribosomes.

Cloverleaf appearance

Has an anticodon that matches to a codon on mRNA

Question 18

What is the function of ribosomal RNA?

Answer 18

This is NON-coding RNA - forms ribosomes together with 7s proteins. As it’s formed it collects in the nucleus (cells that are forming more protein have bigger nuclei for this reason). Processed further in nucleolus and combined with ribosomal proteins to form granular condensation products.

These are then released into the cytoplasm and assembled together to form ribosome.

Question 19

What is the function of micro RNA? Describe its formation.

Answer 19

NON-coding RNA - not translated into proteins.

Regulate gene expression by:
1. Binding to mRNA and repressing translation
2. Destroying mRNA before it’s translated

Formed from precursor primi RNA -> processed in nucleus by microprocessor complex to premi RNA -> further processed in cytoplasm by a DICER enzyme which assembles an RNA induced silencing complex (RISC) which makes miRNA

Question 20

What type of RNA is short interfering RNA? What is its function?

Answer 20

Type of micro RNA. Avoids processing in the nucleus and goes into cytoplasm - binds with RISC to block mRNA translation

Question 21

What direction does DNA replication occur in?

Answer 21

5’ to 3’ direction

Question 22

What is translation?

Answer 22

Formation of protein in the ribosomes from mRNA

Question 23

What is a polyribosome?

Answer 23

Multiple ribosomes linked together as mRNA moves through them

Question 24

What are histones?

Answer 24

Chomosomes wound around small proteins
Can’t form RNA from these as too wound up

Question 25

Describe the order of phases in the cell cycle and say what happens in each one.

Answer 25

Interphase = resting phase between mitosis, covers all of below (cells mostly in G1) (G0 = cell not dividing or preparing to divide) G1 phase = cell making more organelles, synthesising proteins and repairing any damage G1 checkpoint - ensuring cell is correct S phase: DNA replication G2 phase: cell growth, increased cytoplasm Mitosis (M phase) - happens 1-2 hours after S phase

Question 26

What are the 4 phases of mitosis and what happens in each one?

Answer 26

1. Prophase: chromatin in chromosomes is being condensed and nuclear envelope dissolved. Centrosomes being formed. (prometaphase: microtubules start growing from each centromere = aster) 2. Metaphase: centrosomes move to edges of cell and microtubules connect to centromere (middle of chromatid), chromosomes pushed to middle to form equatorial plate 3. Anaphase: chromatids pulled apart to each side of cell 4. Telophase: mitotic apparatus dissipates and ER forms new nuclear membrane. Cell forms contractile ring (contains actin and myosin) and pinches in 2

Question 27

What is the leading strand in DNA replication?

Answer 27

Strand going TOWARDS replication fork

Question 28

What is the lagging strand in DNA replication?

Answer 28

Strand doing AWAY from replication fork

Question 29

What enzyme unwinds DNA to allow replication?

Answer 29

DNA helicase

Question 30

What binds to the DNA strand to determine a starting point for DNA replication?

Answer 30

RNA primer

Question 31

What does DNA polymerase type I exonuclease do?

Answer 31

Proof reads DNA after replication

Question 32

What enzyme is responsible for DNA replication - adding new single pieces of DNA?

Answer 32

DNA polymerase

Question 33

What are Okazaki fragments?

Answer 33

Single pieces of new DNA formed by DNA polymerase

Question 34

What enzyme attaches Okazaki fragments together?

Answer 34

DNA ligase

Question 35

What enzyme removes RNA primers, stopping DNA replication?

Answer 35

Exonuclease

Question 36

What enzyme breaks phosphodiester bonds between DNA nucleotides just before the replication fork, preventing supercoiling. What drugs inhibit this?

Answer 36

Topoisomerase Fluoroquinolones inhibit gyrase (topoisomerase II found only in prokaryotes) which stitches bonds back together

Question 37

What are telomeres and what is their function?

Answer 37

End of chromosomes - contain non-coding DNA so prevent gene loss, as telomeres get shorter with time

Question 38

What is the function of telomerase?

Answer 38

Adds extra telomeres onto end of chromosomes, meaning it can undergo more divisions

Question 39

Describe the structure of a chromosome

Answer 39

2 identical chromatids attached in the centre by a centromere