dna, rna, and proteins. students know and understand the characteristics and structure of living...
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Chapter 13DNA, RNA, and Proteins
Students know and understand the characteristics and structure of living things, the processes of life, and how living things interact with each other and their environment.
Standard 3
Gene DNA Nucleotide Purine Pyrimidine DNA replication DNA helicase
DNA polymerase RNA Gene expression Transcription Translation Codon
Videos approximately 51 minutes.
Vocabulary
DNA is the primary material that causes recognizable, inheritable characteristics in related groups of organisms.
It’s made of two parallel strands of linked subunits called nucleotides.
Each nucleotide is made up of:◦ A phosphate group◦ A 5-carbon sugar molecule
called deoxyribose◦ A nitrogen-containing base
The Structure of DNA: A double helix
DNA Song (2:00)
Information in DNA is contained in the order of the bases.
Base-pairing allows information to be copied.
The sugar and phosphate molecules are the same in every DNA molecule BUT there are four nitrogenous bases:◦ The purines are adenine (A) and guanine (G)◦ The pyrimidines are thymine (T) and cytosine (C)◦ They only pair together as:◦ A—T and C—G or T—A and G—C
Information in DNA (20:00)
The genetic code consists of 64 triplets of nucleotides called codons.
With three exceptions, all of these codons encodes for one of 20 amino acids.
Example: TTA codes for leucine and ATT codes for Isoleucine.
The exceptions are the START and STOP codons.
STOP codons include: TAA, TAG and TGA
Nucleotide sequencing
When DNA replicates, it copies itself.
The DNA molecule unwinds, and the two sides split. Then, new nucleotides are added to each side until two identical sequences result.
Step 1: Unwind and DNA strands separate to form Y-shaped replication forks.
Step 2: Add Complementary Bases Step 3: Formation of Two Identical DNA
Molecules
DNA Replication (1:15)
DNA helicases unwind the DNA
DNA polymerases catalyze the formation of the DNA molecule at the replication fork. They also “proofread” to make sure the replication is perfect. If not, they can go back and remove the incorrect nucleotide, replacing it with the correct one.
Replication proteins
Prokaryotes usually have a single DNA molecule or chromosome that is in a closed loop. Two replication forks begin at a single site, known as the origin of replication. Replication occurs in opposite directions until the forks meet on the other side of the loop.
Eukaryotic cell replication starts at many sites along the chromosome.
Prokaryotic vs. Eukaryotic Replication
Transcription occurs at the first stage of gene expression where the genetic information is transferred from the DNA to the RNA.
Translation occurs as the second stage of gene expression when the RNA translates information to form specific proteins.
Transcription and Translation
RNA is ribonucleic acid. It is usually a single
strand. Nucleotides contain 5-
carbon sugar, ribose rather than deoxyribose.
Instead of thymine, it has the nitrogenous base, uracil.
Uracil (U) with adenine (A).
RNA
Messenger RNA (mRNA) is the type of RNA produced when DNA is transcribed into RNA.
It carries instructions for making a protein from a gene.
Like DNA, each 3-nucleotide sequence is called a codon which is matched to 1 of 20 amino acids.
The genetic code is based on codons that represent a specific amino acid.
START codon: AUG
STOP codons: UAA, UGA
3 Types of RNA: mRNA
Transfer RNA (tRNA) reads the mRNA sequence then turns it into a specific sequence of protein subunits called amino acids.
It decodes and matches the amino acid sequences and places them on growing chains of proteins.
One end of tRNA is an amino acid, the other end has an anticodon which is a 3-nucleotide sequence complementary to an mRNA codon.
tRNAHere’s how it works
Protein production takes place on the ribosomes which are made up of about 80 protein molecules and several large RNA molecules. rRNA is found on the ribosomes.
In eukaryotic cells, where are the ribosomes attached and what does that organelle do to the new proteins?
Ribosomal RNA
Language of Life: Understanding the Genetic Code (27:39)
