Where do proteins enter the respiratory pathway?

During prolonged fasting,the sequence of utilization of energy sources in the body is:

Maximum energy can be obtained from the oxidation of which respiratory substrate?

Choose the incorrect sentence$(s)$ regarding the amphibolic pathway.
$(1)$ Carbohydrates are generally used as substrates for respiration.
$(2)$ Fatty acids can first be degraded into acetyl $CoA$,which enters the respiratory pathway.
$(3)$ In the case of proteins,they are first broken down into amino acids,which are later converted into pyruvic acid and enter the respiratory pathway.
$(4)$ The respiratory pathway is involved in both anabolism and catabolism.
$(5)$ Glycerol would enter the pathway after being converted to $PGAL$.

From the oxidation of one molecule of palmitic acid (fatty acid),the number of $ATP$ molecules gained as net are

Proteins act as respiratory substrates only when: