Question
In mammals, some cell signalling molecules are steroid (lipid) hormones. These hormones are transported in the bloodstream to reach capillary networks.
At a capillary network, hormones pass out of the blood into tissue fluid.
(a) Fig. 3.1 is a diagram of a capillary network.
X body cells tissue fluid
blood blood from to artery vein
Fig. 3.1
(i) Describe the differences between the blood arriving at the arterial end of the capillary network and the tissue fluid surrounding the body cells.
…… [3]
(ii) Not all the tissue fluid passes back into the blood capillaries to enter the bloodstream.
Some of the tissue fluid drains into blind‑ended vessels, such as vessel X shown in
Fig. 3.1.
Name the fluid that is formed in vessel X.
…… [1]
Hormone S is a steroid hormone involved in cell signalling.
Fig. 3.2 shows the sequence of events that occurs when hormone S enters a target cell.
hormone-receptor complex
R
DNA
B
C
G nuclear cell surface envelope membrane
KEY: not to scale hormone S cell surface membrane receptors cytoplasmic receptors nuclear receptor messenger RNA molecule polypeptide
Fig. 3.2
(b) Explain why hormone S, shown in Fig. 3.2, does not need to pass through a transport protein to enter the cytoplasm of the target cell.
…… [2]
(c) The target cell can respond to other cell signalling molecules in addition to hormone S. The cell has receptors in the cell surface membrane, in the cytoplasm and in the nucleus.
Explain why hormone S binds only with receptor R in the cytoplasm and not with the other receptors shown in Fig. 3.2.
…… [1]
(d) The hormone‑receptor complex shown in Fig. 3.2 enters the nucleus and binds to DNA. This switches on a gene coding for a polypeptide that is synthesised in the cytoplasm.
(i) Name the structure through which the hormone‑receptor complex enters the nucleus.
…… [1]
(ii) Name the processes occurring at B and C.
B ……
C …… [2]
(iii) Name structure G.
…… [1]
(e) Cell signalling by hormone S results in the production of a functioning globular protein molecule composed of three identical polypeptide chains.
After the synthesis of these polypeptides, changes need to occur to form the functioning globular protein molecule.
Outline the changes that need to occur to form the functioning globular protein molecule.
…… [4]
[Total: 15]
Mark scheme
3(a)(i) accept from either column for mark and assume blood if not stated 3
any three from
blood tissue fluid
has red blood cells has no red blood cells ;
more, white blood cells / leucocytes / named fewer white blood cells / leucocytes / named ;
e.g. neutrophils, lymphocytes, monocytes e.g. neutrophils, lymphocytes, monocytes
or or
fewer macrophages more macrophages
has platelets has no platelets ;
has, more protein / large proteins has, fewer / no large, proteins ;
or or
has, plasma proteins / named example has no, plasma proteins / named example
e.g albumin / fibrinogen / globulin e.g. albumin / fibrinogen / globulin
these are large proteins only allow fewer plasma proteins if clear the
proteins present are small enough to leave blood
higher, concentration / AW, oxygen lower, concentration / AW, oxygen ;
A more oxygenated A less oxygenated
higher, concentration / AW, glucose / amino lower, concentration / AW, glucose / amino ;
acids / fatty acids acids / fatty acids
lower, concentration / AW, carbon dioxide A urea, higher, concentration / AW, carbon dioxide A ;
in liver / muscles urea, in liver / muscles
I waste I waste
higher pressure lower pressure ;
3(a)(ii) lymph ; A lymphatic fluid 1
3(b) any two from: 2
1 can cross / AW, hydrophobic core (of bilayer) / phospholipid bilayer
or
can pass through gaps between, fatty acid tails / phospholipids ;
2 is, hydrophobic / lipid-soluble / non-polar / not ionic / not charged
or
not, hydrophilic / water-soluble / polar / ionic / charged ;
3 small size ;
3(c) Reject if hormone S or receptor R described as an antigen or enzyme 1
complementary (shape) to / only fits into / specificity for (binding to),
R / receptor ;
3(d)(i) nuclear pore ; A nuclear pores 1
3(d)(ii) B = transcription ; 2
C = translation ;
3(d)(iii) (80S) ribosome ; I 70S 1
3(e) any four from 4
1 (formation of), secondary / 2° / second level, structure with, alpha-helix / α-helix / beta-pleated sheet(s) / β-pleated
sheet(s) ;
A β-conformation for β-pleated sheet
I incorrect detail of bonds
2 folding / coiling, to form tertiary / 3° / third level, structure ;
A ref. to 3D structure as alternative to, folding / coiling
A secondary structure, folds / coils, to form tertiary structure
R alpha helix / beta-pleated sheet, coils / folds
3 two of hydrogen bonds / ionic or electrostatic bonds / disulfide bonds or bridges / hydrophobic interactions ;
I peptide bonds as part of a list that contains two correct bond types
these must be in context of tertiary structure
4 (formation of), quaternary / 4° / fourth level structure ;
A description e.g. polypeptides held together by, interactions / hydrogen bonds / ionic bonds / disulfide bonds
R if peptide bonds included
5 (globular protein) has hydrophilic, amino acids / R-groups / side chains, to, outside / AW ;
ora hydrophobic, amino acids / R-groups / side chains, towards centre / AW
6 example of other post-translational modification ;
e.g. removal, methionine / met
addition sugar group / glycosylation
addition phosphate group / phosphorylation
addition prosthetic group