PLEASE HELP ME! I AM STUCK on 3 BIOLOGY multiple choice questions.

Question

In general, colder temperatures reduce the fluidity of the membrane, so cells will produce different molecules to maintain the proper degree of fluidity. How would the membrane change in response to colder temperatures?

The amount of saturated triacylglycerols would increase.
The amount of unsaturated fatty acids would increase.
The length of the fatty acid side chains in the phospholipids would increase.
The amount of saturated triacylglycerols would decrease.
The amount of unsaturated fatty acids would decrease.

*I think the answer to this is b.

2. Which one of the following statements about a carbon-carbon double bond is CORRECT?

Each of the two carbons is capable of bonding to three other atoms.
The double bond allows free rotation of the molecule at the bond position.
Double bonds are often found in cyclical structures.
The double bond is longer than a corresponding carbon-carbon single bond.
None of the other answer options is correct.

* I have NO IDEA how to answer this one. :(
3. Which one of the following nucleotides could base pair with a pyrimidine?

All of these choices are correct.
cytosine
uracil
thymine
adenine

*Would it be adenine?

I truly appreciate the help. I am taking molecular and cellular biology and I am already struggling two weeks in to the semester. Its so difficult!!!

Answer 1

Regarding the pairing question... the question itself has some assumptions that are worth realizing. Formally, MOST of the nucleotides could form hydrogen bonds with most others... but classroom questions almost always want to know about "in a DNA double helix". The two 'classical' pairs are

Adenine (purine) with thymine (pyrimidine)

Guanine (purine) with cytosine (pyrimidine)

You can explore pairings here:

https://thinkbio.guru/Molecules/BasePairer.php

or see Ade-Thy specifically here:

https://thinkbio.guru/3D_Directory/Flotsam_and_Jetsam/BasePairer/BasePairerQuest.html?instrux=ATpair

 

'Purines' are a CLASS of structures; they have two rings

'Pyrimidines' are a different group; they have one ring

 

One classic mnemonic to help you remember is "PUR As Gold" (PURines are Adenine and Guanine)

Answer 2

Cytosine/C and Thymine/T are pyrimidines in the list. 

 

C always pairs with Guanine/G in both DNA and RNA.

 

T always pairs with Adenine/A in DNA, in RNA T is missing and is replaced by Uracil/U. 

Answer 3

2: Double bonds are found in cyclic structures is the closest one that is correct.  If "cyclic structures" means benzene or another carbocycle.