Molecular biophysics and biochemistry professor Robert Macnab, known for his Scottish accent and efforts to make biochemistry accessible to undergraduates, died Sunday after falling down a flight of stairs in his home. He was 63.

Macnab, who joined the Yale faculty in 1973, served as chairman and director of both undergraduate and graduate studies for the molecular biophysics and biochemistry department and researched the motor bacteria use to swim and how they find food. Colleagues and students recalled his sense of humor, his ability to speak his mind and his devotion to teaching.

Molecular biophysics and biochemistry professor Donald Engelman said Macnab’s wife May, who ran her husband’s lab, came to the lab Monday to help other members of the lab cope.

“We’re all horrified,” Engelman said. “It’s a very unexpected tragedy.”

Macnab was slated to teach “Biochemistry” this semester with molecular biophysics and biochemistry professor Nicholas Ornston. Ornston taught the class alone Monday and plans to continue the class for the semester.

Professors and students describe Macnab as a leader in the department and the University.

He served on several Yale committees including the Executive Committee, Engelman said. He also was a fellow in the Japan Society for Promotion of Science.

But Engelman said Macnab stood out most for his character.

“What comes to mind is his wry sense of humor and his sense of what was right,” Engelman said.

Molecular biophysics and biochemistry professor Dieter Soll, whose lab was next to Macnab’s, said Macnab always spoke his mind.

“Bob was our conscience,” Soll said. “He was an absolutely splendid citizen.”

Soll recalled how hard Macnab worked to put his “Principles of Biochemistry” lecture notes on Microsoft PowerPoint, so that the difficult course would be more accessible to students.

“You could really see his joy that he mastered something that he thought he wouldn’t,” Soll said. “He produced marvelous handouts for the course. I will remember him as a most dedicated and organized lecturer.”

Lydia Finley ’05, who took “Biochemistry” from Macnab last year said he loved the material that he taught and helped students grasp the difficult subject.

“Biochem is not the most welcoming experience, but he made it very accessible to everyone,” Finley said.

Macnab was a brilliant scientist who was open to new ideas, Ornston said.

“His Scotch accent delighted the students as it always did me,” Ornston said.

Soll said Macnab was looking forward to future research on the motor that bacteria use to swim, particularly since he had received high priority for National Institutes of Health funding.

Ornston said for the sake of continuity he would continue to teach “Biochemistry” this semester, without Macnab.