What is DNA? Flashcards
DNA
DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other
organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA). Mitochondria are structures within cells that convert the energy from food into a form that cells can use.
- DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone
4 Chemical Bases That Make Up a Cell’s Code
adenine (A), guanine (G), cytosine (C), and thymine (T).
DNA Bases
Human DNA consists of about 3 billion
bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism. DNA bases pair up with each other, A with T and C with G, to form units called base
pairs.
DNA Base Pairs
A w/ T & C w/ G. Each base is also attached to a sugar molecule and a phosphate molecule.
Together, a base, sugar, and phosphate are called a nucleotide
Nucleotide
a base, sugar, and phosphate. Nucleotides are
arranged in two long strands that form a spiral called a double helix. The structure of the
double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs
and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.
Important property of DNA
that it can replicate, or make copies of itself. Each
strand of DNA in the double helix can serve as a pattern for duplicating the sequence of
bases. This is critical when cells divide because each new cell needs to have an exact
copy of the DNA present in the old cell.
What is noncoding DNA?
Only about 1 percent of DNA is made up of protein-coding genes; the other 99 percent
is noncoding. Noncoding DNA does not provide instructions for making proteins. at least some of it is integral to the function of cells, particularly
the control of gene activity
noncoding DNA contains sequences that act
as regulatory elements, determining when and where
genes are turned on and off.
transcription factors
noncoding DNA elements provide sites for specialized proteins (called transcription factors) to attach
(bind) and either activate or repress the process by which the information from genes is
turned into proteins (transcription).
types of regulatory
elements in Noncoding DNA:
Promoters, Enhancers, Silencers, Insulators
- Promoters
provide binding sites for the protein machinery that carries out
transcription. Promoters are typically found just ahead of the gene on the DNA
strand.
- Enhancers
provide binding sites for proteins that help activate transcription.
Enhancers can be found on the DNA strand before or after the gene they control,
sometimes far away.
- Silencers
provide binding sites for proteins that repress transcription. Like
enhancers, silencers can be found before or after the gene they control and can be
some distance away on the DNA strand.
- Insulators
provide binding sites for proteins that control transcription in a number of
ways. Some prevent enhancers from aiding in transcription (enhancer-blocker
insulators). Others prevent structural changes in the DNA that repress gene activity
(barrier insulators). Some insulators can function as both an enhancer blocker and a
barrier.
RNA molecules
RNA is a chemical cousin of DNA. Other regions of noncoding DNA provide instructions for the formation of certain kinds
of RNA molecules
tRNAs
transfer RNAs specialized RNA
molecules produced from noncoding DNA
rRNAs
ribosomal RNAs help assemble protein building blocks (amino acids) into a chain
that forms a protein
miRNAs
microRNAs which are short lengths of RNA that block
the process of protein production
long noncoding RNAs
lncRNAs which are
longer lengths of RNA that have diverse roles in regulating gene activity
telomeres
protect the ends of chromosomes from being degraded during
the copying of genetic material. structural elements of chromosomes are also part of noncoding DNA
Repetitive noncoding DNA sequences form:
telemeres and satellite DNA
satellite DNA
the basis of
the centromere, which is the constriction point of the X-shaped chromosome pair. also forms heterochromatin, which is densely packed DNA that is
important for controlling gene activity and maintaining the structure of chromosomes
introns
Some noncoding DNA regions located within protein-coding genes
but are removed before a protein is made. Regulatory elements, such as enhancers,
can be located in introns
intergenic regions
Other noncoding regions are found between genes
