Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

6. The Membrane

Introduction to Membrane Transport

General Biology

6. The Membrane

Introduction to Membrane Transport

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3:17 minutes

Problem 4

Textbook Question

Which of the following groups of amino acid residues would likely be found in the portion that crosses the lipid bilayer?
a. Acidic
b. Basic
c. Polar uncharged
d. Nonpolar

Verified step by step guidance

Understand that the lipid bilayer is a hydrophobic environment, meaning it repels water and is composed mainly of nonpolar molecules.

Recognize that amino acids with nonpolar side chains are more likely to be found in the hydrophobic core of the lipid bilayer because they do not interact with water.

Identify the nonpolar amino acids from the image: Glycine (Gly), Alanine (Ala), Valine (Val), Leucine (Leu), Isoleucine (Ile), Methionine (Met), Cysteine (Cys), Phenylalanine (Phe), Tryptophan (Trp), and Proline (Pro).

Consider that polar, acidic, and basic amino acids are more likely to be found on the exterior of the protein or in aqueous environments because they can form hydrogen bonds or ionic interactions with water.

Conclude that the group of amino acid residues most likely to be found in the portion that crosses the lipid bilayer is the nonpolar group.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lipid Bilayer Structure

The lipid bilayer is a fundamental component of cell membranes, composed of two layers of phospholipids. The hydrophobic (water-repelling) tails face inward, while the hydrophilic (water-attracting) heads face outward. This arrangement creates a barrier that separates the interior of the cell from the external environment, influencing which molecules can pass through.

Amino Acid Properties

Amino acids can be classified based on their side chains (R groups) into categories such as polar, nonpolar, acidic, and basic. Nonpolar amino acids have hydrophobic side chains that do not interact favorably with water, making them more likely to be found in the lipid bilayer, while polar and charged amino acids tend to be hydrophilic and interact with the aqueous environment.

Transmembrane Proteins

Transmembrane proteins span the lipid bilayer and often contain regions that interact with both the hydrophobic core of the membrane and the aqueous environments on either side. The portions of these proteins that cross the bilayer typically consist of nonpolar amino acids, allowing them to stabilize within the hydrophobic environment of the membrane.

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