Chapter 13 - DNA Flashcards
What is DNA short for?
Deoxyribosenucleic acid
What are histones?
Special proteins that are bound to DNA
Why are DNA strands coiled around histones?
So that the long molecules can fit into small spaces
What is chromatin?
The tangled network formed by coiled DNA that is not dividing
What are genes?
Sections of DNA molecules
What is the genetic code?
The stored information that determines the structure and activities of the cell
What does each DNA molecule consist of?
- deoxyribose (a 5 carbon sugar)
- a phosphate group
- pairs of nitrogenous bases forming cross-links between the sugar molecules in the two strands
What are the four different nitrogen bases?
- adenine
- thymine
- guanine
- cytosine
What bond is present between the nitrogenous bases?
A weak hydrogen bond
What shape is DNA in?
A double helix
Which base pairs pair up?
A —> T
G —> C
What happens in replication?
- the two linked chains separate because of the weak hydrogen bonds
- these separated sections serve as templates for nucleotides that will form the new half
What is synthesis?
The combing of small molecules to make larger molecules
What does the genetic code in DNA do?
Provides instructions for protein synthesis
Why can different cells make different proteins even though they are identical?
Different genes are activated in different cells
What makes up the genetic code?
The order in which the four bases occur in DNA
What is a triplet?
A sequence of three base that is the code for a particular amino acid
What is DNA?
- a very large molecule made of two strands of nucleotide that are joined by bonds between the nucleotide bases
- the two strands are twisted into a double helix
- found in the nucleus and mitochondria of the cell
Why can DNA not leave the nucleus?
The molecule is too large
What does RNA consist of?
A single strand of sugars and phosphates, with single bases
What is the purpose of RNA only having one strand?
It is small enough to pass through the nuclear pores
What is transcription?
A process by which the mRNA is formed using the code in the DNA molecule
How does transcription start?
Transcription is triggered by chemical messengers that enter the nucleus and bind to the relevant gene
What makes the DNA come apart?
Enzymes called helicases, usually 17 base pairs at a time
What does DNA polymerase do?
Copies the coding from the DNA by forming a complementary mRNA molecule
What tells DNA polymerase to stop copying?
A sequences of bases within the gene
What is mitochondrial DNA?
The DNA found in the mitochondria
What are the differences between DNA found in the nucleus and mitochondrial DNA?
- mitochondrial DNA is in the form of circular molecules that are not bound to proteins
- mtDNA has 37 genes
What do the genes on mtDNA do?
- 24 contain the code for making transfer RNA molecules
- 13 have instructions for making some enzymes involved in cellular respiration
What is acetylation and what does it do?
Acetylation is the adding of an acetyl group (CH3CO) to a histones protein that enhances gene expression
What is methylation and what does it do?
Methylation is the adding of a methyl group (CH3) to a histones which inhibits gene expression
