Chapter 13- RNA and Protein Synthesis

BIG IDEA: How does info. flow from DNA to RNA to direct the synthesis of proteins.

13.1 RNAHow is RNA different from DNA?-Ribonucleic acid, RNA is a nucleic acid consisting of a large chain of nucleotides

3 Important diff. between DNA and RNA:1. sugar is ribose, NOT deoxyribose2. RNA is generally single-stranded instead of

double-stranded3. RNA contains uracil in place of thymine

Functions of RNA:

Messenger RNA (mRNA)- carry info. from DNA to other parts of cell

Ribosomal RNA (rRNA)- subunits that make up proteins

Transfer RNA (tRNA)- transfers each amino acid to the ribosome as specified by the messages in mRNA

How does the cell make RNA?- In transcription, segments of DNA serve as

templates to produce complementary RNA molecules.

- RNA complements base sequences of DNA- RNA polymerase binds DNA to complementary

strand

Promoter- a specific base sequence that tells RNA polymerase where to start and stop RNA synthesis

RNA Editing

Introns- pieces of RNA that are cut out and discarded

Exons- The remaining pieces of RNA that are spliced (put) back together to form the final RNA

13.2 Ribosomes and Protein SynthesisWhat is the genetic code and how is it read? Bases (in the case of RNA)- A,U, C, and G form the genetic code.

Code is read 3 letters @ a time. Each “word” is 3 bases long, and corresponds to an amino acid

Each 3 letter “word”= codon

4 different bases in RNA= 64 different possible 3-base codons

Most amino acids can be specified by more than 1 codon.

Can be read using genetic code table

1. From left to right, write the sequence of mRNA transcribed.

2. Use codon table to translate into amino acids3. Repeat step 1 using complementary strand as new base

GAC AAG TCC ACA ATC

What role does the ribosome play in assembling proteins?- Ribosomes use the sequence of codons in

mRNA to assemble amino acids into polypeptide chains

Translation is the decoding of mRNA→ protein

Steps in Translation1. Begins @ start codon (AUG). Ribosome

attaches to mRNA

2. “EPA” assembly line

3. Continues until ribosome reaches “stop” codon.

Central Dogma of Molecular Biolgy

Information is transferred from DNA → RNA → protein

Gene expression= the in which DNA, RNA, and proteins put genetic info. into action in living cells.

13.3 MutationsMutations are heritable changes in the genetic information

Point mutations -Changes in 1 or a few nucleotides that occur @ a single point

*Substitution- 1 base (A/U/C/G) is changed into a different base. Usually affect 1 amino acid and may have no affect

*Insertion/Deletion (frameshift mutation)- 1 base is inserted or deleted from DNA sequence. Can change every amino acid following the mutation.

Chromosomal mutations: 1) deletion: loss of part or all of chromosome

2) duplication: extra copy of all or parts of chromosome

3) inversion: reversing the direction of parts

4) translocation: part of chromosome breaks off and reattaches to diff. chromosome

What type of mutation?

milk → mile fast → fats

beast → best lot → lost

Some mutations are caused by physical agents in the environment, called mutagens

The effects of mutations can have little/no effect, or can negatively disrupt gene function

Harmful mutations vs. Helpful mutations

Change protein structure or gene activity● Some cancers● Diseases

New or altered functions in proteins that can be useful to organisms in changing environments. ● Genetic diversity● Disease resistance

13.4 Gene Regulation and Expression

To conserve energy prokaryotes transcribe certain genes @ a time. -Regulated by DNA-binding proteins

Operon= group of genes that are regulated together

lac (lactose) operon is on when lactose is present , bacteria knows when it needs nutrients

Promoter=where RNA-polymerase binds to start transcriptionOperator= region that controls rate of transcription

Eukaryotic gene regulation: transcription factors control the expression of genes

● Some open up chromatin to start transcription, some attract RNA polymerase, etc.

● Cell specialization (nerve cells, epithelial,cardiac, etc.)● RNA interface (RNAi) turns genes on and off, plays a role in

growth/development

Cell differentiation = cells become specialization in structure and function

Master control genes (homeotic genes) regulate where specific organs grow in the body

Homeotic genes are like switches that trigger certain patterns of development and differentiation in cells and tissues.